Air Conditioning Basics
Are you considering buying a new air conditioner? Or, are you dissatisfied with the operation of your current air conditioner? Are you unsure whether to fix or replace it? Are you concerned about high summer utility bills? If you answered yes to any of these questions, this publication can help. With it, you can learn about various types of air conditioning systems and how to maintain your air conditioner, hire professional air conditioning services, select a new air conditioner, and ensure that your new air conditioner is properly installed.
Understanding Air Conditioners
Many people buy or use air conditioners without understanding their designs, components, and operating principles. Proper sizing, selection, installation, maintenance, and correct use are keys to cost-effective operation and lower overall costs.
How Air Conditioners Work
Air conditioners employ the same operating principles and basic components as your home refrigerator. An air conditioner cools your home with a cold indoor coil called the evaporator. The condenser, a hot outdoor coil, releases the collected heat outside. The evaporator and condenser coils are serpentine tubing surrounded by aluminum fins. This tubing is usually made of copper. A pump, called the compressor, moves a heat transfer fluid (or refrigerant) between the evaporator and the condenser. The pump forces the refrigerant through the circuit of tubing and fins in the coils. The liquid refrigerant evaporates in the indoor evaporator coil, pulling heat out of indoor air and thereby cooling the home. The hot refrigerant gas is pumped outdoors into the condenser where it reverts back to a liquid giving up its heat to the air flowing over the condenser's metal tubing and fins.
Types of Air Conditioners
The basic types of air conditioners are room air conditioners, split-system central air conditioners, and packaged central air conditioners.
Room Air Conditioners
Room air conditioners cool rooms rather than the entire home. If they provide cooling only where they're needed, room air conditioners are less expensive to operate than central units, even though their efficiency is generally lower than that of central air conditioners.
Smaller room air conditioners (i.e., those drawing less than 7.5 amps of electricity) can be plugged into any 15- or 20-amp, 115-volt household circuit that is not shared with any other major appliances. Larger room air conditioners (i.e., those drawing more than 7.5 amps) need their own dedicated 115-volt circuit. The largest models require a dedicated 230-volt circuit.
Central Air Conditioners
Central air conditioners circulate cool air through a system of supply and return ducts. Supply ducts and registers (i.e., openings in the walls, floors, or ceilings covered by grills) carry cooled air from the air conditioner to the home. This cooled air becomes warmer as it circulates through the home; then it flows back to the central air conditioner through return ducts and registers. A central air conditioner is either a split-system unit or a packaged unit.
In a split-system central air conditioner, an outdoor metal cabinet contains the condenser and compressor, and an indoor cabinet contains the evaporator. In many split-system air conditioners, this indoor cabinet also contains a furnace or the indoor part of a heat pump. The air conditioner's evaporator coil is installed in the cabinet or main supply duct of this furnace or heat pump. If your home already has a furnace but no air conditioner, a split-system is the most economical central air conditioner to install.
In a packaged central air conditioner, the evaporator, condenser, and compressor are all located in one cabinet, which usually is placed on a roof or on a concrete slab next to the house's foundation. This type of air conditioner also is used in small commercial buildings. Air supply and return ducts come from indoors through the home's exterior wall or roof to connect with the packaged air conditioner, which is usually located outdoors. Packaged air conditioners often include electric heating coils or a natural gas furnace. This combination of air conditioner and central heater eliminates the need for a separate furnace indoors.
Maintaining Existing Air Conditioners
Older air conditioners may still be able to offer years of relatively efficient use. However, making your older air conditioner last requires you to perform proper operation and maintenance.
Air Conditioning Problems
One of the most common air conditioning problems is improper operation. If your air conditioner is on, be sure to close your home's windows and outside doors.
Other common problems with existing air conditioners result from faulty installation, poor service procedures, and inadequate maintenance. Improper installation of your air conditioner can result in leaky ducts and low air flow. Many times, the refrigerant charge (the amount of refrigerant in the system) does not match the manufacturer's specifications. If proper refrigerant charging is not performed during installation, the performance and efficiency of the unit is impaired. Service technicians often fail to find refrigerant charging problems or even worsen existing problems by adding refrigerant to a system that is already full. Air conditioner manufacturers generally make rugged, high quality products. If your air conditioner fails, it is usually for one of the common reasons listed below:
refrigerant leaks. If your air conditioner is low on refrigerant, either it was undercharged at installation, or it leaks. If it leaks, simply adding refrigerant is not a solution. A trained technician should fix any leak, test the repair, and then charge the system with the correct amount of refrigerant. Remember that the performance and efficiency of your air conditioner is greatest when the refrigerant charge exactly matches the manufacturer's specification, and is neither undercharged nor overcharged.
inadequate maintenance. If you allow filters and air conditioning coils to become dirty, the air conditioner will not work properly, and the compressor or fans are likely to fail prematurely.
electric control failure. The compressor and fan controls can wear out, especially when the air conditioner turns on and off frequently, as is common when a system is oversized. Because corrosion of wire and terminals is also a problem in many systems, electrical connections and contacts should be checked during a professional service call.
An air conditioner's filters, coils, and fins require regular maintenance for the unit to function effectively and efficiently throughout its years of service. Neglecting necessary maintenance ensures a steady decline in air conditioning performance while energy use steadily increases.
Air Conditioner Filters
The most important maintenance task that will ensure the efficiency of your air conditioner is to routinely replace or clean its filters. Clogged, dirty filters block normal air flow and reduce a system's efficiency significantly. With normal air flow obstructed, air that bypasses the filter may carry dirt directly into the evaporator coil and impair the coil's heat-absorbing capacity. Filters are located somewhere along the return duct's length. Common filter locations are in walls, ceilings, furnaces, or in the air conditioner itself.
Some types of filters are reusable; others must be replaced. They are available in a variety of types and efficiencies. Clean or replace your air conditioning system's filter or filters every month or two during the cooling season. Filters may need more frequent attention if the air conditioner is in constant use, is subjected to dusty conditions, or you have fur-bearing pets in the house.
Air Conditioner Coils
The air conditioner's evaporator coil and condenser coil collect dirt over their months and years of service. A clean filter prevents the evaporator coil from soiling quickly. In time, however, the evaporator coil will still collect dirt. This dirt reduces air flow and insulates the coil which reduces its ability to absorb heat. Therefore, your evaporator coil should be checked every year and cleaned as necessary.
Outdoor condenser coils can also become very dirty if the outdoor environment is dusty or if there is foliage nearby. You can easily see the condenser coil and notice if dirt is collecting on its fins.
You should minimize dirt and debris near the condenser unit. Your dryer vents, falling leaves, and lawn mower are all potential sources of dirt and debris. Cleaning the area around the coil, removing any debris, and trimming foliage back at least 2 feet (0.6 meters) allow for adequate air flow around the condenser.
The aluminum fins on evaporator and condenser coils are easily bent and can block air flow through the coil. Air conditioning wholesalers sell a tool called a "fin comb" that will comb these fins back into nearly original condition.
Sealing and Insulating Air Ducts
An enormous waste of energy occurs when cooled air escapes from supply ducts or when hot attic air leaks into return ducts. Recent studies indicate that 10% to 30% of the conditioned air in an average central air conditioning system escapes from the ducts.
For central air conditioning to be efficient, ducts must be airtight. Hiring a competent professional service technician to detect and correct duct leaks is a good investment, since leaky ducts may be difficult to find without experience and test equipment. Ducts must be sealed with duct "mastic." The old standby of duct tape is ineffective for sealing ducts.
Obstructions can impair the efficiency of a duct system almost as much as leaks. You should be careful not to obstruct the flow of air from supply or return registers with furniture, drapes, or tightly fitted interior doors. Dirty filters and clogged evaporator coils can also be major obstructions to air flow.
The large temperature difference between attics and ducts makes heat conduction through ducts almost as big a problem as air leakage and obstructions. Ducts in attics should be insulated heavily in addition to being made airtight.
Buying New Air Conditioners
Today's best air conditioners use 30% to 50% less energy to produce the same amount of cooling as air conditioners made in the mid 1970s. Even if your air conditioner is only 10 years old, you may save 20% to 40% of your cooling energy costs by replacing it with a newer, more efficient model.
Sizing Air Conditioners
Air conditioners are rated by the number of British Thermal Units (Btu) of heat they can remove per hour. Another common rating term for air conditioning size is the "ton," which is 12,000 Btu per hour.
How big should your air conditioner be? The size of an air conditioner depends on:
how large your home is and how many windows it has;
how much shade is on your home's windows, walls, and roof;
how much insulation is in your home's ceiling and walls;
how much air leaks into your home from the outside; and
how much heat the occupants and appliances in your home generate.
An air conditioner's efficiency, performance, durability, and initial cost depend on matching its size to the above factors.
Make sure you buy the correct size of air conditioner. Two groups—the Air Conditioning Contractors of America (ACCA) and the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE)—publish calculation procedures for sizing central air conditioners. Reputable air conditioning contractors will use one of these procedures, often performed with the aid of a computer, to size your new central air conditioner.
Be aware that a large air conditioner will not provide the best cooling. Buying an oversized air conditioner penalizes you in the following ways.
It costs more to buy a larger air conditioner than you need.
The larger-than-necessary air conditioner cycles on and off more frequently, reducing its efficiency. Frequent cycling makes indoor temperatures fluctuate more and results in a less comfortable environment. Frequent cycling also inhibits moisture removal. In humid climates, removing moisture is essential for acceptable comfort. In addition, this cycling wears out the compressor and electrical parts more rapidly.
A larger air conditioner uses more electricity and creates added demands on electrical generation and delivery systems.
Air Conditioner Efficiency
Each air conditioner has an energy-efficiency rating that lists how many Btu per hour are removed for each watt of power it draws. For room air conditioners, this efficiency rating is the Energy Efficiency Ratio, or EER. For central air conditioners, it is the Seasonal Energy Efficiency Ratio, or SEER. These ratings are posted on an Energy Guide Label, which must be conspicuously attached to all new air conditioners. Many air conditioner manufacturers are participants in the voluntary EnergyStar® labeling program (see Source List in this publication). EnergyStar-labeled appliances mean that they have high EER and SEER ratings.
In general, new air conditioners with higher EERs or SEERs sport higher price tags. However, the higher initial cost of an energy-efficient model will be repaid to you several times during its life span. Your utility company may encourage the purchase of a more efficient air conditioner by rebating some or all of the price difference. Buy the most efficient air conditioner you can afford, especially if you use (or think you will use) an air conditioner frequently and/or if your electricity rates are high.
Room Air Conditioners—EER
Room air conditioners generally range from 5,500 Btu per hour to 14,000 Btu per hour. National appliance standards require room air conditioners built after January 1, 1990, to have an EER of 8.0 or greater. Select a room air conditioner with an EER of at least 9.0 if you live in a mild climate. If you live in a hot climate, select one with an EER over 10.
The Association of Home Appliance Manufacturers reports that the average EER of room air conditioners rose 47% from 1972 to 1991. If you own a 1970s-vintage room air conditioner with an EER of 5 and you replace it with a new one with an EER of 10, you will cut your air conditioning energy costs in half.
Central Air Conditioners—SEER
National minimum standards for central air conditioners require a SEER of 9.7 and 10.0, for single-package and split-systems, respectively. But you do not need to settle for the minimum standard—there is a wide selection of units with SEERs reaching nearly 17.
Before 1979, the SEERs of central air conditioners ranged from 4.5 to 8.0. Replacing a 1970s-era central air conditioner with a SEER of 6 with a new unit having a SEER of 12 will cut your air conditioning costs in half.
Hiring Professional Service
When your air conditioner needs more than the regular maintenance described previously, hire a professional service technician. A well-trained technician will find and fix problems in your air conditioning system. However, not all service technicians are competent. Incompetent service technicians forsake proper diagnosis and perform only minimal stop-gap measures. Insist that the technician:
check for correct amount of refrigerant;
test for refrigerant leaks using a leak detector;
capture any refrigerant that must be evacuated from the system, instead of illegally releasing it to the atmosphere;
check for and seal duct leakage in central systems;
measure air flow through the evaporator coil;
verify the correct electric control sequence and make sure that the heating system and cooling system cannot operate simultaneously;
inspect electric terminals, clean and tighten connections, and apply a non-conductive coating if necessary;
oil motors and check belts for tightness and wear; and
check the accuracy of the thermostat.
Choosing a Contractor
Choosing a contractor may be the most important and difficult task in buying a new central air conditioning system. Ask prospective contractors for recent references. If you are replacing your central air conditioner, tell your contractor what you liked and did not like about the old system. If the system failed, ask the contractor to find out why. The best time to fix existing problems is when a new system is being installed.
When designing your new air conditioning system, the contractor you choose should:
use a computer program or written calculation procedure to size the air conditioner;
provide a written contract listing the main points of your installation that includes the results of the cooling load calculation;
give you a written warranty on equipment and workmanship; and
allow you to hold the final payment until you are satisfied with the new system.
Avoid making your decision solely on the basis of price. The quality of the installation should be your highest priority, because quality will determine energy cost, comfort, and durability.
Installation and Location of Air Conditioners
If your air conditioner is installed correctly, or if major installation problems are found and fixed, it will perform efficiently for years with only minor routine maintenance. However, many air conditioners are not installed correctly. As an unfortunate result, modern energy-efficient air conditioners can perform almost as poorly as older inefficient models.
Be sure that your contractor performs the following procedures when installing a new central air conditioning system:
allows adequate indoor space for the installation, maintenance, and repair of the new system, and installs an access door in the furnace or duct to provide a way to clean the evaporator coil.
uses a duct-sizing methodology such as the Air Conditioning Contractors of America (ACCA) Manual D.
ensures there are enough supply registers to deliver cool air and enough return air registers to carry warm house air back to the air conditioner.
installs duct work within the conditioned space, not in the attic, wherever possible.
seals all ducts with duct mastic and heavily insulates attic ducts.
locates the condensing unit where its noise will not keep you or your neighbors awake at night, if possible.
places the condensing unit in a shady spot, if possible, which can reduce your air conditioning costs by 1% to 2%.
verifies that the newly installed air conditioner has the exact refrigerant charge and air flow rate specified by the manufacturer.
locates the thermostat away from heat sources, such as windows, or supply registers.
If you are replacing an older or failed split system, be sure that the evaporator coil is replaced with a new one that exactly matches the condenser coil in the new condensing unit. (The air conditioner's efficiency will likely not improve if the existing evaporator coil is left in place; in fact, the old coil could cause the new compressor to fail prematurely.)
If you install a new room air conditioner, try to:
locate the air conditioner in a window or wall area near the center of the room and on the shadiest side of the house.
minimize air leakage by fitting the room air conditioner snugly into its opening and sealing gaps with a foam weatherstripping material.
Paying attention to your air conditioning system saves you money and reduces environmental pollution. Notice whether your existing system is running properly, and maintain it regularly. Or, if you need to purchase a new air conditioner, be sure it is sized and installed correctly and has a good EER or SEER rating.
Automatic and Programmable Thermostats
In our modern, high-tech society, we don't think much about some of the electronic gadgets in our homes. Take, for example, the ever-present thermostat—a staple of American households for decades. It usually takes the shape of an unassuming box on the wall, but that modest device controls the comfort of your family on the coldest day in January and the hottest day in July.
What Is a Thermostat?
It is a temperature-sensitive switch that controls a space conditioning unit or system, such as a furnace, air conditioner, or both. When the indoor temperature drops below or rises above the thermostat setting, the switch moves to the "on" position, and your furnace or air conditioner runs to warm or cool the house air to the setting you selected for your family's comfort. A thermostat, in its simplest form, must be manually adjusted to change the indoor air temperature.
General Thermostat Operation
You can easily save energy in the winter by setting the thermostat to 68°F (20°C) when you're at home and awake, and lowering it when you're asleep or away. This strategy is effective and inexpensive if you are willing to adjust the thermostat by hand and wake up in a chilly house. In the summer, you can follow the same strategy with central air conditioning, too, by keeping your house warmer than normal when you are away, and lowering the thermostat setting to 78°F (26°C) only when you are at home and need cooling.
A common misconception associated with thermostats is that a furnace works harder than normal to warm the space back to a comfortable temperature after the thermostat has been set back, resulting in little or no savings. This misconception has been dispelled by years of research and numerous studies. The fuel required to reheat a building to a comfortable temperature is roughly equal to the fuel saved as the building drops to the lower temperature. You save fuel between the time that the temperature stabilizes at the lower level and the next time heat is needed. So, the longer your house remains at the lower temperature, the more energy you save.
Another misconception is that the higher you raise a thermostat, the more heat the furnace will put out, or that the house will warm up faster if the thermostat is raised higher. Furnaces put out the same amount of heat no matter how high the thermostat is set—the variable is how long it must stay on to reach the set temperature.
In the winter, significant savings can be obtained by manually or automatically reducing your thermostat's temperature setting for as little as four hours per day. These savings can be attributed to a building's heat loss in the winter, which depends greatly on the difference between the inside and outside temperatures. For example, if you set the temperature back on your thermostat for an entire night, your energy savings will be substantial. By turning your thermostat back 10° to 15° for 8 hours, you can save about 5% to 15% a year on your heating bill—a savings of as much as 1% for each degree if the setback period is eight hours long. The percentage of savings from setback is greater for buildings in milder climates than for those in more severe climates. In the summer, you can achieve similar savings by keeping the indoor temperature a bit higher when you're away than you do when you're at home.
But there is a certain amount of inconvenience that results from manually controlling the temperature on your thermostat. This includes waking up in a cooler than normal house in the winter and possibly forgetting to adjust the thermostat (during any season) when you leave the house or go to bed.
Thermostats with Automatic Temperature Adjustment
To maximize your energy savings without sacrificing comfort, you can install an automatic setback or programmable thermostat. They adjust the temperature setting for you. While you might forget to turn down the heat before you leave for work in the morning, a programmable thermostat won't! By maintaining the highest or lowest required temperatures for four or five hours a day instead of 24 hours, a programmable thermostat can pay for itself in energy saved within four years.
Programmable thermostats have features with which you may be unfamiliar. The newest generation of residential thermostat technologies is based on microprocessors and thermistor sensors. Most of these programmable thermostats perform one or more of the following energy control functions:
They store and repeat multiple daily settings, which you can manually override without affecting the rest of the daily or weekly program.
They store six or more temperature settings a day.
They adjust heating or air conditioning turn-on times as the outside temperature changes.
Most programmable thermostats have liquid crystal temperature displays. Some have back-up battery packs that eliminate the need to reprogram the time or clock in case of a power failure. New programmable thermostats can be programmed to accommodate life style and control heating and cooling systems as needed
Types of Automatic and Programmable Thermostats
There are five basic types of automatic and programmable thermostats:
Most range in price from $30 to $100, except for occupancy and light sensing thermostats, which cost around $200.
Electromechanical (EM) thermostats, usually the easiest devices to operate, typically have manual controls such as movable tabs to set a rotary timer and sliding levers for night and day temperature settings. These thermostats work with most conventional heating and cooling systems, except heat pumps. EM controls have limited flexibility and can store only the same settings for each day, although at least one manufacturer has a model with separate settings for each day of the week. EM thermostats are best suited for people with regular schedules.
Digital thermostats are identified by their LED or LCD digital readout and data entry pads or buttons. They offer the widest range of features and flexibility, and digital thermostats can be used with most heating and cooling systems. They provide precise temperature control, and they permit custom scheduling. Programming some models can be fairly complicated; make sure you are comfortable with the functions and operation of the thermostat you choose. Remember— you won't save energy if you don't set the controls or you set them incorrectly.
Hybrid systems combine the technology of digital controls with manual slides and knobs to simplify use and maintain flexibility. Hybrid models are available for most systems, including heat pumps.
Occupancy thermostats maintain the setback temperature until someone presses a button to call for heating or cooling. They do not rely on the time of day. The ensuing preset "comfort period" lasts from 30 minutes to 12 hours, depending on how you've set the thermostat. Then, the temperature returns to the setback level. These units offer the ultimate in simplicity, but lack flexibility. Occupancy thermostats are best suited for spaces that remain unoccupied for long periods of time.
Light sensing heat thermostats rely on the lighting level preset by the owner to activate heating systems. When lighting is reduced, a photocell inside the thermostat senses unoccupied conditions and allows space temperatures to fall 10° below the occupied temperature setting. When lighting levels increase to normal, temperatures automatically adjust to comfort conditions. These units do not require batteries or programming and reset themselves after power failures. Light sensing thermostats are designed primarily for stores and offices where occupancy determines lighting requirements, and therefore heating requirements.
Choosing a Programmable Thermostat
Because programmable thermostats are a relatively new technology, you should learn as much as you can before selecting a unit. When shopping for a thermostat, bring information with you about your current unit, including the brand and model number. Also, ask these questions before buying a thermostat:
Does the unit's clock draw its power from the heating systems's low-voltage electrical control circuit instead of a battery? If so, is the clock disrupted when the furnace cycles on and off? Battery-operated, back-up thermostats are preferred by many homeowners.
Is the thermostat compatible with the electrical wiring found in your current unit?
Are you able to install it yourself, or should you hire an electrician or a heating, ventilation, and air conditioning (HVAC) contractor?
How precise is the thermostat?
Are the programming instructions easy to understand and remember? Some thermostats have the instructions printed on the cover or inside the housing box. Otherwise, will you have to consult the instruction booklet every time you want to change the setback times?
Most automatic and programmable thermostats completely replace existing units. These are preferred by many homeowners. However, some devices can be placed over existing thermostats and are mechanically controlled to permit automatic setbacks. These units are usually powered by batteries, which eliminates the need for electrical wiring. They tend to be easy to program, and because they run on batteries, the clocks do not lose time during power outages.
Before you buy a programmable thermostat, chart your weekly habits including wake up and departure times, return home times, and bedtimes, and the temperatures that are comfortable during those times. This will help you decide what type of thermostat will best serve your needs. The following table shows an example of how to chart your weekly habits.
The location of your thermostat can affect its performance and efficiency. Read the manufacturer's installation instructions to prevent "ghost readings" or unnecessary furnace or air conditioner cycling. Place thermostats away from direct sunlight, drafts, doorways, skylights, and windows. Also make sure your thermostat is conveniently located for programming.
Some modern heating and cooling systems require special controls. Heat pumps are the most common and usually require special setback thermostats. These thermostats typically use special algorithms to minimize the use of backup electric resistance heat systems. Electric resistance systems, such as electric baseboard heating, also require thermostats capable of directly controlling 120 volt or 240 volt line-voltage circuits. Only a few companies manufacture line-voltage setback thermostats.
A Note for Heat Pump Owners
When a heat pump is in its heating mode, setting back a conventional heat pump thermostat can cause the unit to operate inefficiently, thereby canceling out any savings achieved by lowering the temperature setting. Maintaining a moderate setting is the most cost-effective practice. Recently, however, some companies have begun selling specially designed setback thermostats for heat pumps, which make setting back the thermostat cost effective. In its cooling mode, the heat pump operates like an air conditioner; therefore, manually turning up the thermostat will save you money.
A Simpler Way to Control Your Environment
The best thermostat for you will depend on your life style and comfort level in varying house temperatures. While automatic and programmable thermostats save energy, a manual unit can be equally effective if you diligently regulate its setting—and if you don't mind a chilly house on winter mornings. If you decide to choose an automatic thermostat, you can set it to raise the temperature before you wake up and spare you some discomfort. It will also perform consistently and dependably to keep your house at comfortable temperatures during the summer heat, as well.
Ask an Energy Expert
Energy Efficiency and Renewable Energy Clearinghouse (EREC)
P.O. Box 3048
Merrifield, VA 22116
Fax: (703) 893-0400
Consumer Energy Information Web Site
Energy experts at EREC provide free general and technical information to the public on many topics and technologies pertaining to energy efficiency and renewable energy.
"Electronic Thermostats," Radio-Electronics, June 1992.
"Energy Saving Thermostats," Consumer Reports, October 1993."
"Good News on the 'Setback' Front," T. Wilson, Home Energy, Jan-Feb 1991. 2124 Kittredge Street, No. 95, Berkeley, CA 94704, (510) 524-5405.
"Get Comfortable with Your Setback Thermostat" (PDF 805 KB), the California Energy Commission.
"Home Environment," Home Mechanix, February 1992.
"Home Q&A," Home Mechanix, November 1995.
"The Latest in Home Thermostats," Consumers' Research Magazine, February 1990.
"New Electronic Thermostats Save Money," Consumers Digest, January 1989.
"Programmable Thermostats: How to Buy and Install One in Your Home," Family Handyman, January 1989.
"Smart Thermostats for Comfort and Conservation," March 1994, EPRI Journal.
This document was produced for the U.S. Department of Energy (DOE) by the National Renewable Energy Laboratory (NREL), a DOE national laboratory.
This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof.
Most people are aware that outdoor air pollution can damage their health but many do not know that indoor air pollution can also have significant health effects. Environmental Protection Agency studies of human exposure to air pollutants indicate that indoor levels of pollutants may be 2-5 times, and occasionally more than 100 times, higher than outdoor levels. These levels of indoor air pollutants may be of particular concern because most people spend about 90% of their time indoors
What are Combustion Pollutants?
Combustion pollutants are gases or particles that come from burning materials. The combustion pollutants discussed in this booklet come from burning fuels in appliances. The common fuels burned in these appliances are natural or LP gas, fuel oil, kerosene, wood, or coal. The types and amounts of pollutants produced depend upon the type of appliance, how well the appliance is installed, maintained, and vented, and the kind of fuel it uses. Some of the common pollutants produced from burning these fuels are carbon monoxide, nitrogen dioxide, particles, and sulfur dioxide. Particles can have hazardous chemicals attached to them. Other pollutants that can be produced by some appliances are unburned hydrocarbons and aldehydes.
Combustion always produces water vapor. Water vapor is not usually considered a pollutant, but it can act as one. It can result in high humidity and wet surfaces. These conditions encourage the growth of biological pollutants such as house dust mites, molds, and bacteria.
Where Do Combustion Pollutants Come From?
Combustion pollutants found indoors include: outdoor air, tobacco smoke, exhaust from car and lawn mower internal combustion engines, and some hobby activities such as welding, woodburning, and soldering. Combustion pollutants can also come from vented or unvented combustion appliances. These appliances include space heaters, gas ranges and ovens, furnaces, gas water heaters, gas clothes dryers, wood or coal-burning stoves, and fireplaces. As a group these are called "combustion appliances."
Breathing high levels of nitrogen dioxide causes irritation of the respiratory tract and causes shortness of breath. Compared to healthy people, children, and individuals with respiratory illnesses such as asthma, may be more susceptible to the effects of nitrogen dioxide.
Some studies have shown that children may have more colds and flu when exposed to low levels of nitrogen dioxide. When people with asthma inhale low levels of nitrogen dioxide while exercising, their lung airways can narrow and react more to inhaled materials.
Sulfur dioxide at low levels of exposure can cause eye, nose, and respiratory tract irritation. At high exposure levels, it causes the lung airways to narrow. This causes wheezing, chest tightness, or breathing problems. People with asthma are particularly susceptible to the effects of sulfur dioxide. They may have symptoms at levels that are much lower than the rest of the population.
How Can I Reduce My Exposure to Combustion Pollutants?
Proper selection, installation, inspection and maintenance of your appliances are extremely important in reducing your exposure to these pollutants. Providing good ventilation in your home and correctly using your appliance can also reduce your exposure to these pollutants.
Additionally, there are several different residential carbon monoxide detectors for sale. The CPSC is encouraging the development of detectors that will provide maximum protection. These detectors would warn consumers of harmful carbon monoxide levels in the home. They may soon be widely available to reduce deaths from carbon monoxide poisoning.
Choose vented appliances whenever possible.
Only buy combustion appliances that have been tested and certified to meet current safety standards. Examples of certifying organizations are Underwriters Laboratories (UL) and the American Gas Association (AGA) Laboratories. Look for a label that clearly shows the certification.
All currently manufactured vented gas heaters are required by industry safety standards to have a safety shut-off device. This device helps protect you from carbon monoxide poisoning by shutting off an improperly vented heater.
Check your local and state building codes and fire ordinances to see if you can use an unvented space heater, if you consider purchasing one. They are not allowed to be used in some communities, dwellings, or certain rooms in the house.
If you must replace an unvented gas space heater with another, make it a new one. Heaters made after 1982 have a pilot light safety system called an oxygen depletion sensor (ODS). This system shuts off the heater when there is not enough fresh air, before the heater begins producing large amounts of carbon monoxide. Look for the label that tells you that the appliance has this safety system. Older heaters will not have this protection system.
Consider buying gas appliances that have electronic ignitions rather than pilot lights. These appliances are usually more energy efficient and eliminate the continuous low-level pollutants from pilot lights.
Buy appliances that are the correct size for the area you want to heat. Using the wrong size heater may produce more pollutants in your home and is not an efficient use of energy.
Talk to your dealer to determine the type and size of appliance you will need. You may wish to write to the appliance manufacturer or association for more information on the appliance. Some addresses are in the back of this booklet.
All new woodstoves are EPA-certified to limit the amounts of pollutants released into the outdoor air. For more information on selecting, installing, operating, and maintaining woodburning stoves, write to the EPA Wood Heater Program. Their address is at the bottom of this booklet. Before buying a woodstove check your local laws about the installation and use of woodstoves.
About Wood Stoves
The burning of wood can produce asthma triggers. It is very important to make sure that wood stoves are properly installed, operated, and maintained to reduce leakage of by-products and to lower the risk for house fires. Check the following links for tips on using your wood stove safely.
Droppings or body parts of cockroaches can be asthma triggers.
Cockroaches are commonly found in crowded cities and the southern United States. Certain proteins, called allergens, are found in cockroach feces and saliva and can cause allergic reactions or trigger asthma symptoms in some individuals. Cockroach allergens likely play a significant role in asthma in many inner-city areas.
Actions You Can Take
An important key to pest management is to free your home of places for pests to hide and to keep them from food and water. Pesticides are toxic for people as well as pests; try to use pest management methods that present the least risk. Some of these methods are:
Do not leave out food or garbage.
Store food in airtight containers.
Clean all food crumbs or spilled liquids right away.
Wash dishes as soon as you are done using them.
Keep counters, sinks, tables and floors clean and clear of clutter.
Fix plumbing leaks and other moisture problems.
Take piles of boxes, newspapers, and other items where cockroaches may hide out of your home.
Make sure trash in your home is properly stored in containers with lids that close securely, and remove trash daily.
Try using poison baits, boric acid, or traps first before using pesticidal sprays.
If sprays are used:
Limit the spray to the infested area.
Do not spray where you prepare or store food, or where young children play, crawl, or sleep.
Carefully follow instructions on the label.
Make sure there is plenty of fresh air when you spray, and keep the person with asthma out of the room while spraying. After spraying, the room should be thoroughly aired out.
What Are Dust Mites?
Dust mites are tiny animals you cannot see. Every home has dust mites. They feed on skin flakes and are found in mattresses, pillows, carpets, upholstered furniture, bedcovers, clothes, stuffed toys, and fabric or other fabric-covered items. Body parts and feces of dust mites can trigger asthma in individuals with an allergic reaction to dust mites. Exposure to dust mite allergen can cause asthma in susceptible children.
Actions You Can Take
Wash bedding (such as sheets, bedcovers, and blankets) once a week in hot water.
Choose washable stuffed toys, wash them often in hot water, and dry thoroughly. Keep stuffed toys off beds.
Cover mattresses and pillows in dust-proof (allergen-impermeable) zippered covers.
Maintain low indoor humidity ideally between 30-50% relative humidity. Humidity levels can be measured by hygrometers which are available at local hardware stores.
About House Dust
House dust may contain asthma triggers.
Actions You Can Take
Remove dust often with a damp cloth. Vacuum carpet, fabric window coverings, and fabric-covered furniture to reduce dust build-up.
Allergic people should leave the area being vacuumed.
Using central vacuums or vacuums with high efficiency filters may be helpful.
When inhaled, ozone can aggravate the lungs and can lead to chest pain, coughing, shortness of breath, and, throat irritation. Ozone may also worsen chronic respiratory diseases such as asthma and compromise the ability of the body to fight respiratory infections. On days when ozone air pollution is the highest, ozone air pollution has been associated with as much as ten percent (10%) to twenty percent (20%) of all summertime respiratory hospital visits and admissions.
People vary widely in their susceptibility to ozone. Healthy people, as well as those with respiratory difficulty, can experience breathing problems when exposed to ozone. Exercise during exposure to ozone causes a greater amount of ozone to be inhaled, and increases the risk of harmful respiratory effects.
Actions You Can Take
State agencies will use television and radio to notify citizens of ozone alerts. On days when your State or local air pollution control agency calls an Ozone Action Day, people with asthma should limit prolonged physical activity outdoors. Consider adjusting outdoor activities to early in the morning or later in the evening.
Also, on Ozone Action Days, you can do the following 10 things to help keep ozone formation to a minimum:
Instead of driving, share a ride, walk or bike.
Take public transportation.
If you must drive, avoid excessive idling and jackrabbit starts.
Don't refuel your car, or only do so after 7 p.m.
Avoid using outboard motors, off-road vehicles, or other gasoline powered recreational vehicles.
Defer mowing your lawn until late evening or the next day. Also avoid using gasoline-powered garden equipment.
Postpone chores that use oil-based paints, solvents, or varnishes that produce fumes.
If you are barbecuing, use an electric starter instead of charcoal lighter fluid.
Limit or postpone your household chores that will involve the use of consumer products.
Conserve energy in your home to reduce energy needs.
Molds can be found almost anywhere; they can grow on virtually any substance when moisture is present. Outdoors, many molds live in the soil and play a key role in the breakdown of leaves, wood, and other plant debris. Without molds we would all be struggling with large amounts of dead plant matter. Molds break down plant materials by digesting them, using the plant material for food.
Molds produce tiny spores to reproduce, just as plants produce seeds. Mold spores waft through the indoor and outdoor air continually. When mold spores land on a damp spot indoors, they may begin growing and digesting whatever they are growing on in order to survive. There are molds that can grow on wood, paper, carpet, foods, even dynamite. When excessive moisture or water accumulates indoors, mold growth will often occur, particularly if the moisture problem remains undiscovered or unaddressed. There is no practical way to eliminate all mold and mold spores in the indoor environment; the way to control indoor mold growth is to control moisture.
Molds can trigger asthma episodes in individuals with an allergic reaction to mold.
Actions You Can Take
If mold is a problem in your home, you must clean up the mold and eliminate sources of moisture.
Wash mold off hard surfaces and dry completely. Absorbent materials, such as ceiling tiles and carpet, may have to be replaced if they are contaminated with mold.
Fix leaky plumbing or other sources of water.
Keep drip pans in your air conditioner, refrigerator, and dehumidifier clean and dry.
Use exhaust fans or open windows in kitchens and bathrooms when showering, cooking, or using the dishwasher.
Vent clothes dryers to the outside.
Maintain low indoor humidity, ideally between 30-50% relative humidity. Humidity levels can be measured by hygrometers which are available at local hardware stores.
What Is Secondhand Smoke?
Secondhand smoke is also known as Environmental Tobacco Smoke. Secondhand smoke includes both exhaled mainstream smoke from smokers and sidestream smoke from the end of a cigarette, cigar, or pipe. Secondhand smoke contains more than 4,000 substances, including over 40 that are linked to cancer. Many of the compounds in tobacco smoke are released at higher rates in sidestream smoke than in mainstream smoke.
How Does Secondhand Smoke Relate To Asthma?
Secondhand smoke may trigger asthma episodes and make asthma symptoms more severe in children who already have asthma. Moreover, secondhand smoke is a risk factor for new cases of asthma in children who have not previously exhibited asthma symptoms.
The means by which secondhand smoke triggers an asthma episode is believed to be through its irritancy effects. That is, smoke irritates the chronically inflamed bronchial passages of asthmatics. This is a different pathway from most of the other environmental triggers of asthma, like dust mites and pet dander, which trigger asthma episodes through allergenic effects.
Exposure to secondhand smoke is also known to cause a variety of other negative health consequences, including lung cancer, ear infections in children, and respiratory illnesses.
Many of the health effects of secondhand smoke (including asthma) are most clearly manifested in children. This is because children are particularly vulnerable to secondhand smoke. This is likely due to several factors, including the fact that children are still developing physically, have higher breathing rates than adults, and have little control over their indoor environments. Children receiving high doses of secondhand smoke, such as those with smoking mothers, run the greatest relative risk of experiencing damaging health effects.
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Your pet’s dead skin flakes, urine, feces, saliva and hair can trigger asthma. Dogs, cats, rodents (including hamsters and guinea pigs) and other mammals all can trigger asthma in individuals with an allergic reaction to animal dander.
Proteins in the dander, urine, or saliva of warm-blooded animals (e.g., cats, dogs, mice, rats, gerbils, birds, etc.) have been reported to sensitize individuals and can cause allergic reactions or trigger asthma episodes in individuals sensitive to animal allergens. The most effective method to control animal allergens in the home is to not allow an animal in the home. If you remove an animal from the home, it is important to clean the home (including floors and walls, but especially carpets and upholstered furniture) thoroughly. Pet allergen levels are reported to stay in the home for several months after the pet is removed even with cleaning. Isolation methods to reduce animal allergen in the home have also been suggested by reputable health authorities (e.g., keeping the animal in only one area of the home, keeping the animal outside, or ensuring the allergic or asthmatic individual stay away from the animal) but the effectiveness of these methods have not been determined. To the contrary, several reports in the literature indicate that animal allergen is carried in the air and by residents of the home on their clothing to all parts of the home, even when the animal is isolated. In fact, animal allergen is often detected in locations where no animals were housed. In these situations, it is assumed that the allergen was carried in on people that have animals or on people that have been around animals or people with animals.
Often people sensitive to animal allergens are advised to wash their pets regularly. Recent research indicates that washing pets may only provide temporary reductions in allergen levels. There is no evidence that this short term reduction is effective in reducing symptoms and it has been suggested that during the washing of the animal the sensitive individual may be initially exposed to higher levels of allergen.
Thus the most effective method to control exposure to animal allergens is to keep your home pet free. However, some individuals may find isolation measures to be sufficiently effective. Isolation measures that have been suggested include keeping pets out of sleeping areas, keeping pets away from upholstered furniture, carpets, and stuffed toys, keeping the pet outdoors as much as possible, and isolating sensitive individuals from the pet as much as possible.
Actions You Can Take
If pets are one of your asthma triggers, you need to strongly consider finding a new home from your pets.
Keep pets out of the bedroom and other sleeping areas at all times, and keep the door closed.
Keep pets away from fabric-covered furniture, carpets and stuffed toys.
Indoor Air Quality Concerns
All of us face a variety of risks to our health as we go about our day-to-day lives. Driving in cars, flying in planes, engaging in recreational activities, and being exposed to environmental pollutants all pose varying degrees of risk. Some risks are simply unavoidable. Some we choose to accept because to do otherwise would restrict our ability to lead our lives the way we want. And some are risks we might decide to avoid if we had the opportunity to make informed choices. Indoor air pollution is one risk that you can do something about.
In the last several years, a growing body of scientific evidence has indicated that the air within homes and other buildings can be more seriously polluted than the outdoor air in even the largest and most industrialized cities. Other research indicates that people spend approximately 90 percent of their time indoors. Thus, for many people, the risks to health may be greater due to exposure to air pollution indoors than outdoors.
In addition, people who may be exposed to indoor air pollutants for the longest periods of time are often those most susceptible to the effects of indoor air pollution. Such groups include the young, the elderly, and the chronically ill, especially those suffering from respiratory or cardiovascular disease.
Prepared by: The Consumer Product Safety Commission (CPSC), and
The American Lung Association, The Christmas Seal People
This guidance will help you understand:
what indoor biological pollution is;
whether your home or lifestyle promotes its development; and,
how to control its growth and buildup.
Outdoor air pollution in cities is a major health problem. Much effort and money continues to be spent cleaning up pollution in the outdoor air. But air pollution can be a problem where you least expect it, in the place you may have thought was safest--your home. Many ordinary activities such as cooking, heating, cooling, cleaning, and redecorating can cause the release and spread of indoor pollutants at home. Studies have shown that the air in our homes can be even more polluted than outdoor air.
Many Americans spend up to 90 percent of their time indoors, often at home. Therefore, breathing clean indoor air can have an important impact on health. People who are inside a great deal may be at greater risk of developing health problems, or having problems made worse by indoor air pollutants. These people include infants, young children, the elderly, and those with chronic illnesses.
What Are Biological Pollutants?
Biological pollutants are or were living organisms. They promote poor indoor air quality and may be a major cause of days lost from work or school, and of doctor and hospital visits. Some can even damage surfaces inside and outside your house. Biological pollutants can travel through the air and are often invisible.
Some common indoor biological pollutants are:
Animal Dander (minute scales from hair, feathers, or skin)
Dust Mite and Cockroach parts
Infectious agents (bacteria or viruses)
Some of these substances are in every home. It is impossible to get rid of them all. Even a spotless home may permit the growth of biological pollutants. Two conditions are essential to support biological growth: nutrients and moisture. These conditions can be found in many locations, such as bathrooms, damp or flooded basements, wet appliances (such as humidifiers or air conditioners), and even some carpets and furniture.
Modern materials and construction techniques may reduce the amount of outside air brought into buildings which may result in high moisture levels inside. Using humidifiers, unvented heaters, and air conditioners in our homes has increased the chances of moisture forming on interior surfaces. This encourages the growth of certain biological pollutants
The Scope Of The Problem
Most information about sources and health effects of biological pollutants is based on studies of large office buildings and two surveys of homes in northern U.S. and Canada. These surveys show that 30% to 50% of all structures have damp conditions which may encourage the growth and buildup of biological pollutants. This percentage is likely to be higher in warm, moist climates.
Some diseases or illnesses have been linked with biological pollutants in the indoor environment. However, many of them also have causes unrelated to the indoor environment. Therefore, we do not know how many health problems relate only to poor indoor air.
Health Effects Of Biological Pollutants
All of us are exposed to biological pollutants. However, the effects on our health depend upon the type and amount of biological pollution and the individual person. Some people do not experience health reactions from certain biological pollutants, while others may experience one or more of the following reactions:
Except for the spread of infections indoors, ALLERGIC REACTIONS may be the most common health problem with indoor air quality in homes. They are often connected with animal dander (mostly from cats and dogs), with house dust mites (microscopic animals living in household dust), and with pollen. Allergic reactions can range from mildly uncomfortable to life-threatening, as in a severe asthma attack. Some common signs and symptoms are:
Runny nose and sneezing
Wheezing and difficulty breathing
Health experts are especially concerned about people with asthma. These people have very sensitive airways that can react to various irritants, making breathing difficult. The number of people who have asthma has greatly increased in recent years. The number of people with asthma has gone up by 59 percent since 1970, to a total of 9.6 million people. Asthma in children under 15 years of age has increased 41 percent in the same period, to a total of 2.6 million children. The number of deaths from asthma is up by 68 percent since 1979, to a total of almost 4,400 deaths per year.
INFECTIOUS DISEASES caused by bacteria and viruses, such as flu, measles, chicken pox, and tuberculosis, may be spread indoors. Most infectious diseases pass from person to person through physical contact. Crowded conditions with poor air circulation can promote this spread. Some bacteria and viruses thrive in buildings and circulate through indoor ventilation systems. For example, the bacterium causing Legionnaire's disease, a serious and sometimes lethal infection, and Pontiac Fever, a flu-like illness, have circulated in some large buildings.
Talking To Your Doctor
Are you concerned about the effects on your health that may be related to biological pollutants in your home? Before you discuss your concerns with your doctor, you should know the answers to the following questions. This information can help the doctor determine whether your health problems may be related to biological pollution.
Does anyone in the family have frequent headaches, fevers, itchy watery eyes, a stuffy nose, dry throat, or a cough? Does anyone complain of feeling tired or dizzy all the time? Is anyone wheezing or having difficulties breathing on a regular basis?
Did these symptoms appear after you moved to a new or different home?
Do the symptoms disappear when you go to school or the office or go away on a trip, and return when you come back?
Have you recently remodeled your home or done any energy conservation work, such as installing insulation, storm windows, or weather stripping? Did your symptoms occur during or after these activities?
Does your home feel humid? Can you see moisture on the windows or on other surfaces, such as walls and ceilings?
What is the usual temperature in your home? Is it very hot or cold?
Have you recently had water damage?
Is your basement wet or damp?
Is there any obvious mold or mildew?
Does any part of your home have a musty or moldy odor?
Is the air stale?
Do you have pets?
Do your house plants show signs of mold?
Do you have air conditioners or humidifiers that have not been properly cleaned?
Does your home have cockroaches or rodents?
TOXIC REACTIONS are the least studied and understood health problem caused by some biological air pollutants in the home. Toxins can damage a variety of organs and tissues in the body, including the liver, the central nervous system, the digestive tract, and the immune system.
Checking Your Home
There is no simple and cheap way to sample the air in your home to determine the level of all biological pollutants. Experts suggest that sampling for biological pollutants is not a useful problem-solving tool. Even if you had your home tested, it is almost impossible to know which biological pollutant(s) cause various symptoms or health problems. The amount of most biological substances required to cause disease is unknown and varies from one person to the next.
Does this make the problem sound hopeless? On the contrary, you can take several simple, practical actions to help remove sources of biological pollutants, to help get rid of pollutants, and to prevent their return.Self-Inspection: A Walk Through Your Home
Begin by touring your household. Follow your nose, and use your eyes. Two major factors help create conditions for biological pollutants to grow: nutrients and constant moisture with poor air circulation.
Dust and construction materials, such as wood, wallboard, and insulation, contain nutrients that allow biological pollutants to grow. Firewood also is a source of moisture, fungi, and bugs.
Appliances such as humidifiers, kerosene and gas heaters, and gas stoves add moisture to the air.
A musty odor, moisture on hard surfaces, or even water stains, may be caused by:
- Air-conditioning units
- Basements, attics, and crawlspaces
- Heating and air-conditioning ducts
- Humidifiers and dehumidifiers
- Refrigerator drip pans
What You Can Do About Biological Pollutants
Before you give away the family pet or move, there are less drastic steps that can be taken to reduce potential problems. Properly cleaning and maintaining your home can help reduce the problem and may avoid interrupting your normal routine. People who have health problems such as asthma, or are allergic, may need to do this and more. Discuss this with your doctor.
Water in your home can come from many sources. Water can enter your home by leaking or by seeping through basement floors. Showers or even cooking can add moisture to the air in your home. The amount of moisture that the air in your home can hold depends on the temperature of the air. As the temperature goes down, the air is able to hold less moisture. This is why, in cold weather, moisture condenses on cold surfaces (for example, drops of water form on the inside of a window). This moisture can encourage biological pollutants to grow.
There are many ways to control moisture in your home:
Fix leaks and seepage. If water is entering the house from the outside, your options range from simple landscaping to extensive excavation and waterproofing. (The ground should slope away from the house.) Water in the basement can result from the lack of gutters or a water flow toward the house. Water leaks in pipes or around tubs and sinks can provide a place for biological pollutants to grow.
Put a plastic cover over dirt in crawlspaces to prevent moisture from coming in from the ground. Be sure crawlspaces are well-ventilated.
Use exhaust fans in bathrooms and kitchens to remove moisture to the outside (not into the attic). Vent your clothes dryer to the outside.
Turn off certain appliances (such as humidifiers or kerosene heaters) if you notice moisture on windows and other surfaces.
Use dehumidifiers and air conditioners, especially in hot, humid climates, to reduce moisture in the air, but be sure that the appliances themselves don't become sources of biological pollutants.
Raise the temperature of cold surfaces where moisture condenses. Use insulation or storm windows. (A storm window installed on the inside works better than one installed on the outside.) Open doors between rooms (especially doors to closets which may be colder than the rooms) to increase circulation. Circulation carries heat to the cold surfaces. Increase air circulation by using fans and by moving furniture from wall corners to promote air and heat circulation. Be sure that your house has a source of fresh air and can expel excessive moisture from the home.
Pay special attention to carpet on concrete floors. Carpet can absorb moisture and serve as a place for biological pollutants to grow. Use area rugs which can be taken up and washed often. In certain climates, if carpet is to be installed over a concrete floor, it may be necessary to use a vapor barrier (plastic sheeting) over the concrete and cover that with sub-flooring (insulation covered with plywood) to prevent a moisture problem.
Moisture problems and their solutions differ from one climate to another. The Northeast is cold and wet; the Southwest is hot and dry; the South is hot and wet; and the Western Mountain states are cold and dry. All of these regions can have moisture problems. For example, evaporative coolers used in the Southwest can encourage the growth of biological pollutants. In other hot regions, the use of air conditioners which cool the air too quickly may prevent the air conditioners from running long enough to remove excess moisture from the air. The types of construction and weatherization for the different climates can lead to different problems and solutions.
Maintain and Clean All Appliances That Come In Contact With Water
Have major appliances, such as furnaces, heat pumps and central air conditioners, inspected and cleaned regularly by a professional, especially before seasonal use. Change filters on heating and cooling systems according to manufacturer's directions. (In general, change filters monthly during use.) When first turning on the heating or air conditioning at the start of the season, consider leaving your home until it airs out.
Have window or wall air-conditioning units cleaned and serviced regularly by a professional, especially before the cooling season. Air conditioners can help reduce the entry of allergy-causing pollen. But they may also become a source of biological pollutants if not properly maintained. Clean the coils and incline the drain pans according to manufacturer's instructions, so water cannot collect in pools.
Have furnace-attached humidifiers cleaned and serviced regularly by a professional, especially before the heating season.
Follow manufacturer's instructions when using any type of humidifier. Experts differ on the benefits of using humidifiers. If you do use a portable humidifier (approximately 1 to 2 gallon tanks), be sure to empty its tank every day and refill with distilled or demineralized water, or even fresh tap water if the other types of water are unavailable. For larger portable humidifiers, change the water as recommended by the manufacturer. Unplug the appliance before cleaning. Every third day, clean all surfaces coming in contact with water with a 3% solution of hydrogen peroxide, using a brush to loosen deposits. Some manufacturers recommend using diluted household bleach for cleaning and maintenance, generally in a solution of one-half cup bleach to one gallon water. When using any household chemical, rinse well to remove all traces of chemical before refilling humidifier.
Empty dehumidifiers daily and clean often. If possible, have the appliance drip directly into a drain. Follow manufacturer's instructions for cleaning and maintenance. Always disconnect the appliance before cleaning.
Clean refrigerator drip pans regularly according to manufacturer's instructions. If refrigerator and freezer doors don't seal properly, moisture may build up and mold can grow. Remove any mold on door gaskets and replace faulty gaskets.
Clean mold surfaces, such as showers and kitchen counters.
Remove mold from walls, ceilings, floors, and paneling. Do not simply cover mold with paint, stain, varnish, or a moisture-proof sealer, as it may resurface.
Replace moldy shower curtains, or remove them and scrub well with a household cleaner and rinse before re-hanging them.
Controlling dust is very important for people who are allergic to animal dander and mites. You cannot see mites, but you can either remove their favorite breeding grounds or keep these areas dry and clean. Dust mites can thrive in sofas, stuffed chairs, carpets, and bedding. Open shelves, fabric wallpaper, knickknacks, and venetian blinds are also sources of dust mites. Dust mites live deep in the carpet and are not removed by vacuuming. Many doctors suggest that their mite-allergic patients use washable area rugs rather than wall-to-wall carpet.
Always wash bedding in hot water (at least 130° F "one hundred degrees Fahrenheit") to kill dust mites. Cold water won't do the job. Launder bedding at least every 7 to 10 days.
Use synthetic or foam rubber mattress pads and pillows, and plastic mattress covers if you are allergic. Do not use fuzzy wool blankets, feather or wool-stuffed comforters, and feather pillows.
Clean rooms and closets well; dust and vacuum often to remove surface dust. Vacuuming and other cleaning may not remove all animal dander, dust mite material, and other biological pollutants. Some particles are so small they can pass through vacuum bags and remain in the air. If you are allergic to dust, wear a mask when vacuuming or dusting. People who are highly allergy-prone should not perform these tasks. They may even need to leave the house when someone else is cleaning.
Before You Move
Protect yourself by inspecting your potential new home. If you identify problems, have the landlord or seller correct them before you move in, or even consider moving elsewhere.
Have professionals check the heating and cooling system, including humidifiers and vents. Have duct lining and insulation checked for growth.
Check for exhaust fans in bathrooms and kitchens. If there are no vents, do the kitchen and bathrooms have at least one window apiece? Does the cooktop have a hood vented outside? Does the clothes dryer vent outside? Are all vents to the outside of the building, not into attics or crawlspaces?
Look for obvious mold growth throughout the house, including attics, basements, and crawlspaces, and around the foundation. See if there are many plants close to the house, particularly if they are damp and rotting. They are a potential source of biological pollutants. Downspouts from roof gutters should route water away from the building.
Look for stains on the walls, floor or carpet (including any carpet over concrete floors) as evidence of previous flooding or moisture problems. Is there moisture on windows and surfaces? Are there signs of leaks or seepage in the basement?
Look for rotted building materials which may suggest moisture or water damage.
If you or anyone else in the family has a pet allergy, ask if any pets have lived in the home.
Examine the design of the building. Remember that in cold climates, overhanging areas, rooms over unheated garages, and closets on outside walls may be prone to problems with biological pollutants.
Look for signs of cockroaches.
Where Biological Pollutants May Be Found In The Home
Dirty air conditioners
Dirty humidifiers and/or dehumidifiers
Bathroom without vents or windows
Kitchen without vents or windows
Dirty refrigerator drip pans
Laundry room with unvented dryer
Carpet on damp basement floor
Closet on outside wall
Dirty heating/air conditioning system
dogs or cats
Water damage (around windows, the roof, or the basement)
Warning! Carefully read instructions for use and any cautionary labeling on cleaning products before beginning cleaning procedures.
Do not mix any chemical products. Especially, never mix cleaners containing bleach with any product (such as ammonia) which does not have instructions for such mixing. When chemicals are combined, a dangerous gas can sometimes be formed.
Household chemicals may cause burning or irritation to skin and eyes.
Household chemicals may be harmful if swallowed, or inhaled.
Avoid contact with skin, eyes, mucous membranes and clothing.
Avoid breathing vapor. Open all windows and doors and use an exhaust fan that sends the air outside.
Keep household chemicals out of reach of children.
Rinse treated surface areas well to remove all traces of chemicals.
Correcting Water Damage
What if damage is already done? Follow these guidelines for correcting water damage:
Throw out mattresses, wicker furniture, straw baskets and the like that have been water damaged or contain mold. These cannot be recovered.
Discard any water-damaged furnishings such as carpets, drapes, stuffed toys, upholstered furniture and ceiling tiles, unless they can be recovered by steam cleaning or hot water washing and thorough drying.
Remove and replace wet insulation to prevent conditions where biological pollutants can grow.
Additional Sources of Information
Contact your local American Lung Association for copies of: Indoor Air Pollution Fact Sheets, Air Pollution in Your Home? and other publications on indoor air pollution.
Contact the U.S. Consumer Product Safety Commission, Washington, D.C. 20207, for copies of Humidifier Safety Alert.
To report an unsafe consumer product or product-related health problem, consumers may call the U.S. Consumer Product Safety Commission at 1-800-638-2772. A teletypewriter for the hearing impaired is available at 1-800-638-8270; the Maryland TTY number is 1-800-492-8104.
You may also contact EPA's IAQ INFO Clearinghouse at 1-800-438-4318 (or (703) 356-4020) for more information on indoor air quality and to order publications from the list of IAQ publications
You're coughing and sneezing and tired and achy. You think that you might be getting a cold. Later, when the medicines you've been taking to relieve the symptoms of the common cold are not working and you've now got a terrible headache, you finally drag yourself to the doctor. After listening to your history of symptoms and perhaps doing a sinus X-ray, the doctor says you have sinusitis.
Sinusitis simply means inflammation of the sinuses, but this gives little indication of the misery and pain this condition can cause. Chronic sinusitis, sinusitis that recurs frequently, affects an estimated 32 million people in the United States. Americans spend millions of dollars each year for medications that promise relief from their sinus symptoms.
Sinuses are hollow air spaces, of which there are many in the human body. When people say, "I'm having a sinus attack," they usually are referring to symptoms in one or more of four pairs of cavities, or spaces, known as paranasal sinuses. These cavities, located within the skull or bones of the head surrounding the nose, include the frontal sinuses over the eyes in the brow area, the maxillary sinuses inside each cheekbone, the ethmoids just behind the bridge of the nose and between the eyes, and behind them, the sphenoids in the upper region of the nose and behind the eyes.
Each sinus has an opening into the nose for the free exchange of air and mucus, and each is joined with the nasal passages by a continuous mucous membrane lining. Therefore, anything that causes a swelling in the nose-an infection or an allergic reaction-also can affect the sinuses. Air trapped within an obstructed sinus, along with pus or other secretions, may cause pressure on the sinus wall. The result is the sometimes intense pain of a sinus attack. Similarly, when air is prevented from entering a paranasal sinus by a swollen membrane at the opening, a vacuum can be created that also causes pain.
Sinusitis has its own localized pain signals, depending upon the particular sinus affected. Headache upon awakening in the morning is characteristic of sinus involvement. Pain when the forehead over the frontal sinuses is touched may indicate inflammation of the frontal sinuses. Infection in the maxillary sinuses can cause the upper jaw and teeth to ache and the cheeks to become tender to the touch. Since the ethmoid sinuses are near the tear ducts in the corner of the eyes, inflammation of these cavities often causes swelling of the eyelids and tissues around the eyes and pain between the eyes. Ethmoid inflammation also can cause tenderness when the sides of the nose are touched, a loss of smell, and a stuffy nose. Although the sphenoid sinuses are less frequently affected, infection in this area can cause earaches, neck pain, and deep aching at the top of the head.
Other symptoms of sinusitis can include fever, weakness, tiredness, a cough that may be more severe at night, and runny nose or nasal congestion. In addition, drainage of mucus from the sphenoids down the back of the throat (postnasal drip) can cause a sore throat and can irritate the membranes lining the larynx (upper windpipe).
Most cases of acute sinusitis are caused by viruses and will clear up without treatment within two weeks. Viruses can enter the body through the nasal passages and set off a chain reaction resulting in sinusitis. For example, the nose reacts to an invasion by viruses that cause infections such as the common cold, flu, or measles by producing mucus and sending white blood cells to the lining of the nose, which congest and swell the nasal passages. When this swelling involves the adjacent mucous membranes of the sinuses, air and mucus are trapped behind the narrowed openings of the sinuses. If the sinus openings become too narrow to permit drainage of the mucus, then bacteria, which normally are present in the respiratory tract, begin to multiply. Most apparently healthy people harbor bacteria, such as Streptococcus pneumoniae and Haemophilus influenzae, in their upper respiratory tracts with no ill effects until the body's defenses are weakened or drainage from the sinuses is blocked by a cold or other viral infection. The bacteria that may have been living harmlessly in the nose, throat, or sinus area can multiply and cause an acute sinus infection.
Medicines, too, can set off a nasal reaction with accompanying sinusitis. For example, intolerance to aspirin and other related non-steroidal anti-inflammatory medications, such as ibuprofen, can be associated with sinusitis in patients with asthma or nasal polyps (small growths on the mucous membrane lining of the sinuses).
Sometimes, fungal infections can cause acute sinusitis. Although these organisms are abundant in the environment, they usually are harmless to healthy people, indicating that the human body has a natural resistance to them. Fungi, such as Aspergillus and Curvularia, can cause serious illness, in people whose immune systems are not functioning properly. Some people with fungal sinusitis have an allergic-type reaction to the fungi.
Chronic inflammation of the nasal passages (rhinitis) also can lead to sinusitis. Allergic rhinitis or hay fever (discussed below) is the most common cause of chronic sinusitis and is a frequent cause of acute sinusitis. Vasomotor rhinitis, caused by humidity, cold air, alcohol, perfumes, and other environmental conditions, also can result in a sinus infection.
Chronic sinusitis refers to inflammation of the sinuses that continues for weeks, months, or even years.
As noted above, allergies are the most common cause of chronic sinusitis. Inhalation of airborne allergens (foreign substances that provoke an allergic reaction), such as dust, mold, and pollen, often set off allergic reactions (allergic rhinitis) that, in turn, may contribute to sinusitis. People who are allergic to fungi can develop a condition called "allergic fungal sinusitis." As body cells react against these inhaled substances, they release chemical compounds, such as histamine, at the mucosal surface. These chemicals then cause the nasal passages to swell and block drainage from the sinuses, resulting in sinusitis.
Damp weather, especially in northern temperate climates, or pollutants in the air and in buildings also can affect people subject to chronic sinusitis.
Chronic sinusitis can be caused by structural abnormalities of the nose, such as a deviated septum (the bony partition separating the two nasal passages), or by small growths called nasal polyps, both of which can trap mucus in the sinuses.
Although a stuffy nose can occur in other conditions, like the common cold, many people confuse simple nasal congestion with sinusitis. A cold, however, usually lasts about seven days and disappears without treatment. Acute sinusitis often lasts longer than a week. A doctor can diagnose sinusitis by medical history, physical examination, X-rays, and if necessary, MRIs or CT scans (magnetic resonance imaging and computed tomography).
After diagnosing sinusitis and identifying a possible cause, a doctor can prescribe a course of treatment that will clear up the source of the inflammation and relieve the symptoms.
Sinusitis is treated by re-establishing drainage of the nasal passages, controlling or eliminating the source of the inflammation, and relieving the pain. Doctors generally recommend decongestants to reduce the congestion, antibiotics to control a bacterial infection, if present, and pain relievers to reduce the pain.
Over-the-counter and prescription decongestant nose drops and sprays, however, should not be used for more than a few days. When used for longer periods, these drugs can lead to even more congestion and swelling of the nasal passages.
If symptoms do not improve within 10 to 14 days, the cause of sinusitis is likely to be bacterial. Most patients with sinusitis that is caused by bacteria can be treated successfully with antibiotics used along with a nasal or oral decongestant. A narrow-spectrum antibiotic -- one that fights the most common bacteria -- is the initial treatment recommended.
For many years, the combination of allergic disease and infectious sinusitis has been considered the most difficult form of sinus disease to treat. The patient with uncontrolled nasal allergies frequently experiences a lot of congestion, swelling, excess secretions, and discomfort in the sinus areas. Therefore, the patient should work with a doctor who understands the diagnosis and treatment of allergic diseases to pinpoint the cause of the allergies and follow an allergy care program to help alleviate sinusitis.
Doctors often prescribe steroid nasal sprays, along with other treatments, to reduce the congestion, swelling, and inflammation of sinusitis. Because steroid nasal sprays have no serious side effects, they can be used for long-term treatment. In some people, however, they irritate the nasal passages.
For patients with severe chronic sinusitis, a doctor may prescribe oral steroids, such as prednisone. Because oral steroids can have significant side effects, they are prescribed only when other medications have not been effective.
Although sinus infection cannot be cured by home remedies, people can use them to lessen their discomfort. Inhaling steam from a vaporizer or a hot cup of water can soothe inflamed sinus cavities. Another treatment is saline nasal spray, which can be purchased in a pharmacy. A hot water bottle; hot, wet compresses; or an electric heating pad applied over the inflamed area also can be comforting.
In treating patients with severe sinusitis, a physician may use special procedures. One technique requires the patient to lie on his back with his head over the edge of the examining table. A decongestant fluid is placed in the nose, and air is suctioned out of the nose so that the decongestant fluid can shrink the sinus membranes sufficiently to permit drainage. Or, a thin tube can be inserted into the sinuses for washing out entrapped pus and mucus.
Sometimes, however, surgery is the only alternative for preventing chronic sinusitis. In children, problems often are eliminated by removal of adenoids obstructing nasal-sinus passages. Adults who have had allergic and infectious conditions over the years sometimes develop polyps that interfere with proper drainage. Removal of these polyps and/or repair of a deviated septum to ensure an open airway often provides considerable relief from sinus symptoms. The most common surgery done today is functional endoscopic sinus surgery, in which the natural openings from the sinuses are enlarged to allow drainage.
Although people cannot prevent all sinus disorders-any more than they can avoid all colds or bacterial infections-they can take certain measures to reduce the number and severity of the attacks and possibly prevent sinusitis from becoming chronic. Appropriate amounts of rest, a well-balanced diet, and exercise can help the body function at its most efficient level and maintain a general resistance to infections. Eliminating environmental factors, such as climate and pollutants, is not always possible, but they can often be controlled.
Many people with sinusitis find partial relief from their symptoms when humidifiers are installed in their homes, particularly if room air is heated by a dry forced-air system. Air conditioners help to provide an even temperature, and electrostatic filters attached to heating and air conditioning equipment are helpful in removing allergens from the air.
A person susceptible to sinus disorders, particularly one who also is allergic, should avoid cigarette smoke and other air pollutants. Inflammation in the nose caused by allergies predisposes a patient to a strong reaction to all irritants. Drinking alcohol also causes the nasal-sinus membranes to swell.
Sinusitis-prone persons may be uncomfortable in swimming pools treated with chlorine, since it irritates the lining of the nose and sinuses. Divers often experience congestion with resulting infection when water is forced into the sinuses from the nasal passages.
Air travel, too, poses a problem for the individual suffering from acute or chronic sinusitis. A bubble of air trapped within the body expands as air pressure in a plane is reduced. This expansion causes pressure on surrounding tissues and can result in a blockage of the sinuses or the eustachian tubes in the ears. The result may be discomfort in the sinus or middle ear during the plane's ascent or descent. Doctors recommend using decongestant nose drops or inhalers before the flight to avoid this difficulty.
People who suspect that their sinus inflammation may be related to dust, mold, pollen, or food-or any of the hundreds of allergens that can trigger a respiratory reaction-should consult a doctor. Various tests can determine the cause of the allergy and also help the doctor recommend steps to reduce or limit allergy symptoms.
NIAID, a component of the National Institutes of Health, supports research on AIDS, tuberculosis and other infectious diseases as well as allergies and immunology.
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Identifying Air Quality Problems
Some health effects can be useful indicators of an indoor air quality problem, especially if they appear after a person moves to a new residence, remodels or refurnishes a home, or treats a home with pesticides. If you think that you have symptoms that may be related to your home environment, discuss them with your doctor or your local health department to see if they could be caused by indoor air pollution. You may also want to consult a board-certified allergist or an occupational medicine specialist for answers to your questions.
Another way to judge whether your home has or could develop indoor air problems is to identify potential sources of indoor air pollution. Although the presence of such sources does not necessarily mean that you have an indoor air quality problem, being aware of the type and number of potential sources is an important step toward assessing the air quality in your home.
A third way to decide whether your home may have poor indoor air quality is to look at your lifestyle and activities. Human activities can be significant sources of indoor air pollution. Finally, look for signs of problems with the ventilation in your home. Signs that can indicate your home may not have enough ventilation include moisture condensation on windows or walls, smelly or stuffy air, dirty central heating and air cooling equipment, and areas where books, shoes, or other items become moldy. To detect odors in your home, step outside for a few minutes, and then upon reentering your home, note whether odors are noticeable.
Indoor Air and Your Health
Health effects from indoor air pollutants may be experienced soon after exposure or, possibly, years later.
Immediate effects may show up after a single exposure or repeated exposures. These include irritation of the eyes, nose, and throat, headaches, dizziness, and fatigue. Such immediate effects are usually short-term and treatable. Sometimes the treatment is simply eliminating the person's exposure to the source of the pollution, if it can be identified. Symptoms of some diseases, including asthma, hypersensitivity pneumonitis, and humidifier fever, may also show up soon after exposure to some indoor air pollutants.
The likelihood of immediate reactions to indoor air pollutants depends on several factors. Age and preexisting medical conditions are two important influences. In other cases, whether a person reacts to a pollutant depends on individual sensitivity, which varies tremendously from person to person. Some people can become sensitized to biological pollutants after repeated exposures, and it appears that some people can become sensitized to chemical pollutants as well.
Certain immediate effects are similar to those from colds or other viral diseases, so it is often difficult to determine if the symptoms are a result of exposure to indoor air pollution. For this reason, it is important to pay attention to the time and place the symptoms occur. If the symptoms fade or go away when a person is away from the home and return when the person returns, an effort should be made to identify indoor air sources that may be possible causes. Some effects may be made worse by an inadequate supply of outdoor air or from the heating, cooling, or humidity conditions prevalent in the home.
Other health effects may show up either years after exposure has occurred or only after long or repeated periods of exposure. These effects, which include some respiratory diseases, heart disease, and cancer, can be severely debilitating or fatal. It is prudent to try to improve the indoor air quality in your home even if symptoms are not noticeable.
While pollutants commonly found in indoor air are responsible for many harmful effects, there is considerable uncertainty about what concentrations or periods of exposure are necessary to produce specific health problems. People also react very differently to exposure to indoor air pollutants. Further research is needed to better understand which health effects occur after exposure to the average pollutant concentrations found in homes and which occur from the higher concentrations that occur for short periods of time.
Measuring Pollutant Levels
The federal government recommends that you measure the level of radon in your home. Without measurements there is no way to tell whether radon is present because it is a colorless, odorless, radioactive gas. Inexpensive devices are available for measuring radon. EPA provides guidance as to risks associated with different levels of exposure and when the public should consider corrective action. There are specific mitigation techniques that have proven effective in reducing levels of radon in the home.
For pollutants other than radon, measurements are most appropriate when there are either health symptoms or signs of poor ventilation and specific sources or pollutants have been identified as possible causes of indoor air quality problems. Testing for many pollutants can be expensive. Before monitoring your home for pollutants besides radon, consult your state or local health department or professionals who have experience in solving indoor air quality problems in non-industrial buildings.
There are many types and sizes of air cleaners on the market, ranging from relatively inexpensive table-top models to sophisticated and expensive whole-house systems. Some air cleaners are highly effective at particle removal, while others, including most table-top models, are much less so. Air cleaners are generally not designed to remove gaseous pollutants.
The effectiveness of an air cleaner depends on how well it collects pollutants from indoor air (expressed as a percentage efficiency rate) and how much air it draws through the cleaning or filtering element (expressed in cubic feet per minute). A very efficient collector with a low air-circulation rate will not be effective, nor will a cleaner with a high air-circulation rate but a less efficient collector. The long-term performance of any air cleaner depends on maintaining it according to the manufacturer's directions.
Another important factor in determining the effectiveness of an air cleaner is the strength of the pollutant source. Table-top air cleaners, in particular, may not remove satisfactory amounts of pollutants from strong nearby sources. People with a sensitivity to particular sources may find that air cleaners are helpful only in conjunction with concerted efforts to remove the source.
Over the past few years, there has been some publicity suggesting that houseplants have been shown to reduce levels of some chemicals in laboratory experiments. There is currently no evidence, however, that a reasonable number of houseplants remove significant quantities of pollutants in homes and offices. Indoor houseplants should not be over-watered because overly damp soil may promote the growth of microorganisms which can affect allergic individuals.
At present, EPA does not recommend using air cleaners to reduce levels of radon and its decay products. The effectiveness of these devices is uncertain because they only partially remove the radon decay products and do not diminish the amount of radon entering the home. EPA plans to do additional research on whether air cleaners are, or could become, a reliable means of reducing the health risk from radon. EPA's booklet, Residential Air-Cleaning Devices, provides further information on air-cleaning devices to reduce indoor air pollutants.
For most indoor air quality problems in the home, source control is the most effective solution.
Usually the most effective way to improve indoor air quality is to eliminate individual sources of pollution or to reduce their emissions. Some sources, like those that contain asbestos, can be sealed or enclosed; others, like gas stoves, can be adjusted to decrease the amount of emissions. In many cases, source control is also a more cost-efficient approach to protecting indoor air quality than increasing ventilation because increasing ventilation can increase energy costs. Specific sources of indoor air pollution in your home are listed later in this section.
Another approach to lowering the concentrations of indoor air pollutants in your home is to increase the amount of outdoor air coming indoors. Most home heating and cooling systems, including forced air heating systems, do not mechanically bring fresh air into the house. Opening windows and doors, operating window or attic fans, when the weather permits, or running a window air conditioner with the vent control open increases the outdoor ventilation rate. Local bathroom or kitchen fans that exhaust outdoors remove contaminants directly from the room where the fan is located and also increase the outdoor air ventilation rate.
It is particularly important to take as many of these steps as possible while you are involved in short-term activities that can generate high levels of pollutants--for example, painting, paint stripping, heating with kerosene heaters, cooking, or engaging in maintenance and hobby activities such as welding, soldering, or sanding. You might also choose to do some of these activities outdoors, if you can and if weather permits.
Weatherizing Your Home
The federal government recommends that homes be weatherized in order to reduce the amount of energy needed for heating and cooling. While weatherization is underway, however, steps should also be taken to minimize pollution from sources inside the home. In addition, residents should be alert to the emergence of signs of inadequate ventilation, such as stuffy air, moisture condensation on cold surfaces, or mold and mildew growth. Additional weatherization measures should not be undertaken until these problems have been corrected.
Weatherization generally does not cause indoor air problems by adding new pollutants to the air. (There are a few exceptions, such as caulking, that can sometimes emit pollutants.) However, measures such as installing storm windows, weather stripping, caulking, and blown-in wall insulation can reduce the amount of outdoor air infiltrating into a home. Consequently, after weatherization, concentrations of indoor air pollutants from sources inside the home can increase.
What Causes Indoor Air Problems?
Indoor pollution sources that release gases or particles into the air are the primary cause of indoor air quality problems in homes. Inadequate ventilation can increase indoor pollutant levels by not bringing in enough outdoor air to dilute emissions from indoor sources and by not carrying indoor air pollutants out of the home. High temperature and humidity levels can also increase concentrations of some pollutants.
There are many sources of indoor air pollution in any home. These include combustion sources such as oil, gas, kerosene, coal, wood, and tobacco products; building materials and furnishings as diverse as deteriorated, asbestos-containing insulation, wet or damp carpet, and cabinetry or furniture made of certain pressed wood products; products for household cleaning and maintenance, personal care, or hobbies; central heating and cooling systems and humidification devices; and outdoor sources such as radon, pesticides, and outdoor air pollution.
The relative importance of any single source depends on how much of a given pollutant it emits and how hazardous those emissions are. In some cases, factors such as how old the source is and whether it is properly maintained are significant. For example, an improperly adjusted gas stove can emit significantly more carbon monoxide than one that is properly adjusted.
Some sources, such as building materials, furnishings, and household products like air fresheners, release pollutants more or less continuously. Other sources, related to activities carried out in the home, release pollutants intermittently. These include smoking, the use of unvented or malfunctioning stoves, furnaces, or space heaters, the use of solvents in cleaning and hobby activities, the use of paint strippers in redecorating activities, and the use of cleaning products and pesticides in housekeeping. High pollutant concentrations can remain in the air for long periods after some of these activities.
Amount of Ventilation
If too little outdoor air enters a home, pollutants can accumulate to levels that can pose health and comfort problems. Unless they are built with special mechanical means of ventilation, homes that are designed and constructed to minimize the amount of outdoor air that can "leak" into and out of the home may have higher pollutant levels than other homes. However, because some weather conditions can drastically reduce the amount of outdoor air that enters a home, pollutants can build up even in homes that are normally considered "leaky."