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Energy Efficiency & Indoor Air Quality

HUD USER Home > Energy-Efficient and Healthy Homes > Energy Efficiency & Indoor Air Quality > Indoor Air Pollutants

Indoor Air Pollutants > Fuel-Burning Appliances

Eliminating individual sources of pollution and reducing pollutant emissions from specific sources is a cost-effective and efficient way to improve indoor air quality. For example, fuel-burning appliances such as gas-fired or oil-fired furnaces, water heaters, and clothes dryers as well as gas stoves, kerosene and gas space heaters, and fireplaces should be properly vented to prevent backdrafts of harmful pollutants such as carbon monoxide, nitrogen dioxide, and particles. Learn more about backdrafting at the U.S. Environmental Protection Agency’s website.

To learn more about source-specific pollution control techniques for fuel burning appliances, visit this link.

Indoor Air Pollutants > Volatile Organic Compounds

Volatile organic compounds (VOC) are carbon-containing compounds that can be emitted as gases at room temperature from certain products such as building materials, furnishings, paints and varnishes, cleansers and disinfectants, pesticides, printers, and glues and adhesives. Exposure to VOCs may have short- and long-term adverse health effects, and the extent and nature of these effects depend on factors such as the level and duration of exposure.

Formaldehyde, a VOC commonly found in homes, can be emitted from pressed wood products containing urea-formaldehyde resins. Examples of pressed wood products include particleboard, hardwood plywood paneling, and fiberboard used in subflooring, cabinets, wall paneling, and other furnishings. Other sources of formaldehyde include urea-formaldehyde foam insulation, durable press drapes, fuel-burning appliances such as gas stoves and kerosene space heaters, and glues. Adverse health effects of formaldehyde exposure include irritation of the eyes, nose, and throat. High concentrations of formaldehyde can trigger asthma attacks and may cause cancer.

To reduce exposure to VOCs, ensure adequate ventilation while using products that emit VOCs, use paints labeled “low-VOC” or “no-VOC,” use “exterior-grade” pressed wood products (containing phenol resins instead of urea resins) that emit less formaldehyde, carefully follow precautions on product labels, and avoid storing opened containers of paints and varnishes within the home. Air conditioners and dehumidifiers ensure moderate temperatures and reduce humidity levels, which in turn reduce indoor levels of formaldehyde and other VOCs.

For more information on VOCs, visit the following links:

Indoor Air Pollutants > Radon

Radon is a colorless and odorless radioactive gas produced from the natural radioactive decay of uranium found in rocks, soil, and water. Radon gas typically moves up through the ground into the air, and it can enter houses and other buildings through cracks and openings in the foundation and floor. Because of its radioactive properties, radon is a health hazard when concentrated in enclosed spaces, and prolonged exposure to high levels of radon can cause lung cancer. According to the U.S. Environmental Protection Agency, radon is the second-leading cause of lung cancer in the United States, led only by smoking.

To assess indoor radon levels, consumers can purchase do-it-yourself radon test kits from a hardware store or hire a qualified technician. If tests reveal that radon levels are higher than four picocuries per liter of air (pCi/L), consumers are advised to hire a qualified radon contractor to reduce their home’s radon levels. Contractors typically use techniques such as soil suction, which prevents radon from entering a home by drawing the radon from below the home and venting it through a pipe to the outside. Using radon-resistant construction methods for new homes can also prevent high radon levels.

For more detailed information on radon, visit the following links:


Indoor Air Pollutants > Moisture and Mold

In addition to damaging building materials, excessive moisture in homes can cause poor indoor air quality. High humidity not only can increase the concentration of volatile organic compounds and other air pollutants in the home, but it can also cause mold growth. This section describes measures to control moisture and prevent and remedy mold in homes.


As air flows through openings or gaps in the building envelope, moisture moves with it. Moisture can also enter buildings by heat transfer or diffusion through building materials, although most building materials significantly impede moisture diffusion.

Strategies for controlling moisture levels depend on the climate and type of building construction. Recommended moisture control strategies include fixing plumbing or other water leaks, sealing air leaks, and adding insulation to reduce heat transfer through the building envelope. Vapor diffusion retarders, which can be installed in basements, crawlspaces, floors, ceilings, and walls, control moisture movement by reducing the rate at which water vapor moves through a material.

Using air conditioners, dehumidifiers, and exhaust fans (in kitchens and bathrooms) and ensuring proper ventilation can prevent the buildup of excessive moisture in homes. In addition, moisture-generating appliances such as stoves and clothes dryers should be vented to the outside whenever possible. Other strategies to control indoor moisture levels include keeping roof gutters clean and in good repair and having an effective rainwater drainage system to ensure that rainwater is diverted away from the home’s walls and foundation.

For more detailed information on moisture control techniques, visit the following links:


Molds are naturally present both outdoors and indoors. Although outdoor molds help break down dead organic matter such as fallen leaves and dead trees, mold growth indoors contributes to poor air quality. Molds cause allergic reactions and respiratory problems such as asthma and damage the surface on which it grows.

Mold grows when airborne spores come in contact with wet surfaces, so the most effective way to prevent or remedy indoor mold growth is to control indoor moisture levels.

If mold is found in a home, occupants must take steps to clean the mold and eliminate the moisture sources causing the mold growth. According to the U.S. Environmental Protection Agency (EPA), most mold growth covering an area of less than 10 square feet can be handled without the help of a professional. However, if the mold covers more than 10 square feet or was caused by contaminated water, a professional should be hired to remove the mold.

Residents can clean small areas of mold on hard surfaces by scrubbing with detergent and water and then drying the area completely. Porous or absorbent materials such as carpeting and ceiling tiles that are contaminated with mold may need to be replaced. Biocides such as chlorine bleach are generally not recommended for routine mold cleanup.

During mold cleanup, workers should use a respirator and goggles to limit exposure to mold and wear appropriate gloves to protect their hands from the detergents or disinfectants used to remove the mold. Refer to EPA's mold cleanup guidelines to learn more about mold cleaning techniques and the precautionary measures to be taken while cleaning up mold.

If mold is suspected in a home’s heating, ventilation, and air conditioning system, refer to the EPA guide “Should You Have the Air Ducts in Your Home Cleaned?” for information on how to address the issue.

For detailed information on remediation and prevention of mold, visit the following links: