Improving Indoor Air Quality
The information provided here is based on current scientific and technical understanding of the issues presented. Following the advice given will not necessarily provide complete protection in all situations or against all health hazards that may be caused by indoor air pollution.
There are three basic strategies to improve indoor air quality:
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.
For most indoor air quality problems in the home, source control is the most effective solution.
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.
Advanced designs of new homes are starting to feature mechanical systems that bring outdoor air into the home. Some of these designs include energy-efficient heat recovery ventilators (also known as air-to-air heat exchangers).
- For more information about whole house ventilation system options, see the U.S. Dept. of Energy's Energy Saver: Whole-House Ventilation.
Ventilation and shading can help control indoor temperatures. Ventilation also helps remove or dilute indoor airborne pollutants coming from indoor sources. This reduces the level of contaminants and improves indoor air quality (IAQ). Carefully evaluate using ventilation to reduce indoor air pollutants where there may be outdoor sources of pollutants, such as smoke or refuse, nearby.
The introduction of outdoor air is one important factor in promoting good air quality. Air may enter a home in several different ways, including:
- through natural ventilation, such as through windows and doors
- through mechanical means, such as through outdoor air intakes associated with the heating, ventilation and air conditioning (HVAC) system
- through infiltration, a process by which outdoor air flows into the house through openings, joints and cracks in walls, floors and ceilings, and around windows and doors.
Infiltration occurs in all homes to some extent.
Natural ventilation describes air movement through open windows and doors. If used properly natural ventilation can at times help moderate the indoor air temperature, which may become too hot in homes without air-conditioning systems or when power outages or brownouts limit or make the use of air conditioning impossible.
Natural ventilation can also improve indoor air quality by reducing pollutants that are indoors. Examples of natural ventilation are:
- opening windows and doors
- window shading such as closing the blinds
Most residential forced air-heating systems and air-conditioning systems do not bring outdoor air into the house mechanically, and infiltration and natural ventilation are relied upon to bring outdoor air into the home. Advanced designs for new homes are starting to add a mechanical feature that brings outdoor air into the home through the HVAC system. Some of these designs include energy efficient heat recovery ventilators to mitigate the cost of cooling and heating this air during the summer and winter.
- the technical assistance webinar Do Residential Ventilation Rates Affect Respiratory Health? presented by Dr. William Fisk of the Lawrence Berkeley National Laboratory on the EPA YouTube channel.
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.