Indoor Air Quality at Home: How to Monitor It and How to Improve It

What causes poor indoor air, and the signs to watch for

The EPA says indoor pollution sources that release gases or particles into the air are the primary cause of indoor air quality problems. Its list of sources includes fuel-burning appliances, tobacco products, new flooring or carpet, and some pressed wood furniture. It also lists cleaning and hobby products, central heating and cooling systems, excess moisture, and outdoor sources such as radon and pesticides.

Too little outdoor air makes things worse. The EPA says inadequate ventilation can raise pollutant levels by not diluting indoor emissions and not carrying them out. The EPA adds that high temperature and humidity levels can also increase concentrations of some pollutants. Our guide to good humidity for a house covers the target range.

The EPA says some health effects may show up soon after exposure, and these include irritation of the eyes, nose, and throat, headaches, dizziness, and fatigue. It says certain of these effects are similar to those from colds or other viral diseases. Its advice is to notice the time and place symptoms occur. If they fade when a person leaves the area, look for indoor sources. If someone has symptoms that may be related to an indoor air pollutant, the EPA suggests considering a talk with a health care provider.

Home air monitors: what they measure and what they miss

The EPA calls these devices low-cost air pollution monitors. Each uses one or more sensors to report on specific pollutants or on conditions such as temperature and humidity. The EPA says most sold in the U.S. are designed to detect gases or particles such as particulate matter (PM), radon, carbon monoxide (CO), carbon dioxide (CO2), formaldehyde or volatile organic compounds (VOCs), or conditions such as temperature and humidity.

Volatile organic compounds (VOCs) are chemicals that the EPA says are emitted as gases from certain solids or liquids, such as paints and cleaners.

The limits matter as much as the readings. The EPA says a monitor only detects what it was designed for. A monitor that measures only PM, it notes, would not alert you to radon or carbon monoxide. It also says there are no widely accepted indoor limits for most pollutants. So the alert levels on a monitor are set by its maker.

The EPA says the cost of a monitor does not necessarily indicate how well it will perform. It also says all monitors have a limited lifespan and can become less reliable over time. The EPA does not generally test these monitors indoors, and it does not endorse any brand.

How to place a monitor and read it sensibly

The EPA says to follow the maker's instructions, because ignoring them may compromise performance. In general, it suggests placing the monitor in the breathing zone. For a typical adult, it gives that as about 3 to 6 feet off the floor, sitting or standing.

Keep it away from walls that block air flow into the device. The EPA also says to avoid spots right next to stoves, fireplaces or stored cleaning products. It also says drafts, such as near air conditioning or heater vents or open windows, could impact the results.

The EPA suggests comparing readings before, during and after an activity like cooking. If PM rises while you cook, it suggests turning on a range hood or opening a window or door.

The EPA says a detected pollutant does not necessarily mean an indoor air quality problem exists. It adds that in some cases you may need a professional to identify or resolve the concern.

Two tests a monitor does not replace: carbon monoxide and radon

Carbon monoxide (CO) is a colorless, odorless gas which at high levels can cause serious illness and death, according to the EPA. The EPA says alerts from home air monitors are not designed to warn of immediate danger, unlike CO alarms and smoke detectors. It says CO alarms should be certified to the current UL Standard 2034 or another standard it names. UL stands for Underwriters Laboratory, as the EPA writes it. For where alarms go, see our guide to carbon monoxide detector placement.

Radon is a radioactive gas that the EPA says forms naturally in rocks, soil and groundwater. People can be exposed to radon mainly by breathing air that comes through cracks and gaps in homes, the EPA says. The EPA says radon is the number one cause of lung cancer among non-smokers, by its estimates.

The Florida Department of Health says the only way to tell if your home has a radon problem is to test for it. The EPA gives radon levels in picocuries per liter (pCi/L). The EPA recommends fixing a home at 4 pCi/L or more. It also says to consider fixing between 2 and 4 pCi/L, since no level is known to be safe.

The Florida Department of Health says Florida certified radon measurement businesses can test your home. It says anyone offering professional radon services must hold its Radon Certification. At present, EPA does not recommend using air cleaners to reduce levels of radon and its decay products.

Improving the air: source control first

The EPA says usually the most effective way to improve indoor air quality is to remove sources or cut their emissions. It gives examples. Materials containing asbestos can be sealed or enclosed, and gas stoves can be adjusted to emit less. Adjusting a gas appliance is work for a licensed gas contractor, not a homeowner task.

If you use products such as paint or paint stripper only occasionally or seasonally, the EPA suggests buying only as much as you will use right away. It notes these products can release organic compounds while in use and, to some degree, while stored. It also says to increase ventilation when using products that emit VOCs.

The EPA says there is currently no evidence that a reasonable number of houseplants remove significant quantities of pollutants in homes. The EPA also says products like air fresheners can release pollutants more or less continuously.

Then outdoor air, then air cleaning

The EPA says most home heating and cooling systems do not mechanically bring fresh air into the house. It suggests opening windows and doors when the weather permits. It also points to bathroom and kitchen fans that exhaust outdoors. It says to use these steps most during painting, cooking, sanding and similar short-term activities. Our ventilation guide covers how Florida humidity affects this choice.

Air cleaning comes last. The EPA says filtration can be an effective supplement to source control and ventilation, but it does not replace them. The EPA says portable air cleaners are designed to filter the air in a single room or area. Central heating, ventilation and air conditioning (HVAC) filters are designed to filter air throughout a home.

For a portable unit, the EPA suggests a clean air delivery rate (CADR) large enough for the room. The EPA says the higher the CADR, the more particles the unit can filter and the larger the area it can serve, and the CADR system is for particles only. The EPA says portable air cleaners often achieve a high CADR by using a high-efficiency particulate air (HEPA) filter. For gases, the EPA says to choose a portable air cleaner with an activated carbon filter or other filter designed to remove gases. It says air cleaners are generally not designed to remove gases.

The EPA says to avoid air cleaners that intentionally produce ozone, a gas it calls a lung irritant. It says no federal agency has approved ozone generators for use in occupied spaces. For central system filters, see our guide to HVAC air filters.