Common Sources of Indoor Air Pollution

Contrary to popular belief, indoor air is commonly two to five times more polluted than outdoor air, according to the Environmental Protection Agency. Studies confirm this trend in rural and urban dwellings alike. This suggests that builders and occupants have a lot of options when it comes to minimizing exposure to pollutants.Indoor air quality ranks as one of the top five environmental health risks, and numerous illnesses are linked to airborne contaminants. Gaining an awareness of common sources of indoor air contamination is instrumental in promoting overall occupant health.Biological Contaminants

Mold, pet dander, viruses, bacteria, dust mites, and pollen are all common indoor air pollutants. Many of these are also common asthma and allergy triggers. Adequate ventilation and filtration of incoming air are essential in mitigating exposure.

It is important to determine the Minimum Efficiency Reporting Value (MERV) rating of air filters when pollen, bacteria, dust mites, pet dander, and mold spores are a concern. Filters with a higher MERV can remove smaller particles, often making them superior in improving indoor air quality for certain contaminants.

Air filters with a MERV between 1 and 4 primarily protect HVAC equipment, and many particles of concern can still pass through the filter. Air filters with a medium MERV of 5 to 11 are reasonably effective in removing airborne pollutants. Filters with a MERV of 12 or greater are the most efficient in trapping biological contaminants, promoting high indoor air quality.

Proper maintenance can also promote indoor air quality. Mold can develop when there are leaks in the building envelope or plumbing system. It is important to inspect for and repair any leaks to prevent mold growth.

Elevated moisture levels in bathrooms, basements, and mechanical rooms can also encourage the growth of mold and dust mite populations. This can be mitigated with an effective ventilation strategy that maintains ideal humidity levels by exhausting excess moisture. Keep in mind that exhaust-only ventilation systems may not be appropriate for projects with tight building envelopes if there isn’t adequate makeup air to allow these systems to operate properly. Exhaust fans may also pull in pollutants from other indoor and outdoor sources. A balanced ventilation system with optional high-MERV air filters is ideal in promoting indoor air quality. The Zehnder ComfoAir heat recovery ventilators and energy recovery ventilators provide a stream of fresh, filtered air while exhausting an equal quantity of stale air. The exhaust and intake air streams are separated, preventing cross-contamination.Combustion AppliancesWood stoves, cooking ranges, fireplaces, heaters, and chimneys are all common sources of carbon monoxide, nitrogen dioxide, and particles. Combustion gases can also enter homes through malfunctioning chimneys and flues or from cracked furnace heat exchangers. It is important to regularly inspect and repair damage to flues, furnaces, and chimneys. Keep in mind that airborne pollutants from chimneys, stoves, and atmospherically vented hot water heaters commonly backdraft in highly weatherized homes and buildings without a dedicated air supply.

This is especially common when exhaust-only ventilation is used because it can create negative pressure inside the dwelling. Balanced ventilation systems, including heat recovery ventilators and energy recovery ventilators, help prevent this by supplying and exhausting equal amounts of air, preventing a vacuum from forming inside the dwelling.

Household Products

Numerous common household products are of concern when considering indoor air quality. Varnishes, paints, and waxes are common sources of volatile organic compounds that can pollute the air. Other products used by occupants can also be problematic, such as cleaning, hobby, and personal care products.

Reducing exposure to volatile organic compounds involves eliminating or limiting the use of toxic products or using a product as safely as possible. Labels commonly provide information on safe use and may advise ensuring proper ventilation or only using a product outdoors. It is best to avoid exposure whenever possible to methylene chloride and benzene by avoiding use of products that contain these chemicals or ensuring proper ventilation when they are necessary.

Storing toxic products can also increase the quantity of volatile organic compounds indoors. Whenever possible, safely dispose of unneeded products and avoid needlessly storing them on the premises.

Ensuring adequate ventilation rates for your project also helps protect indoor air quality, as some degree of indoor air pollution is inevitable. Ventilation dilutes the pollutants, and thus adequate ventilation rates for both intake and exhaust air are essential.


Found in many building products and household products and as a byproduct of combustion, formaldehyde is a known human carcinogen. Adhesives and engineered wood products are two common sources of indoor pollution from formaldehyde. Whenever possible, avoid products containing high levels of formaldehyde and create a ventilation strategy to keep formaldehyde exposure to a minimum.

This blog was developed by Zehnder America. All posts, sponsored and un-sponsored have been reviewed and approved by the Sustainable Community Media Editorial Team to ensure quality, relevance/usefulness and objectivity.

Topics: Energy Recovery & Heat Recovery, Indoor Air Quality, Ventilation

Companies: Zehnder America

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