Indoor Air Quality Testing: What to Measure and How

Indoor air in most homes contains more pollutants than outdoor air. The EPA estimates that indoor air can be two to five times more polluted than outdoor air, and sometimes more. This is partly because modern homes are tightly sealed and ventilated less than older buildings, and partly because we have filled them with materials that off-gas synthetic compounds.

The list of potential indoor air pollutants is long: mold spores, volatile organic compounds (VOCs) from paints and adhesives, formaldehyde from engineered wood, radon from soil, carbon dioxide from occupants and combustion, particulates from cooking and candles, and more. Not all of these are present in every home at concerning levels. The question is which ones might be present in your home, and at what concentrations.

This guide covers the main indoor air quality concerns, how to test for each, and what to do with the results.

When Testing Makes Sense

Not every home needs comprehensive indoor air quality testing. Testing makes the most sense when:

• You or someone in your home has unexplained symptoms: headaches, fatigue, eye or throat irritation, respiratory problems that improve when you leave the house and return when you come back
• You have had a water intrusion event (flooding, plumbing leak, roof leak) and want to verify that mold has not established
• You are buying an older home or renovating a space with unknown material history
• You have completed a renovation and want to confirm that VOC levels have returned to acceptable ranges before full occupancy
• You have a basement or live in an area with known radon risk
• You have young children, elderly family members, or people with respiratory conditions who are more sensitive to air quality problems

If none of these apply and you have no symptoms, a full air quality assessment may not be necessary. Starting with a radon test (simple, inexpensive, and relevant to most homes) is a reasonable baseline step regardless of other concerns.

Mold Testing

Mold is one of the most common indoor air quality concerns. Visible mold is not always present even when mold is a problem: mold can grow inside walls, in attics, in HVAC ductwork, and in crawl spaces, producing spores that enter the living area without obvious surface growth.

Air sampling

Air sampling for mold uses a pump that draws a measured volume of air through a collection medium (either a spore trap cassette or an agar plate). The sample is sent to a laboratory that identifies and counts the spore types present. Results are compared to outdoor control samples taken at the same time: indoor mold counts should generally be lower than outdoor counts, and the species composition should be similar. Elevated indoor counts or the presence of water-damage indicator species (Stachybotrys, Chaetomium, or high Aspergillus/Penicillium) suggests a mold problem.

Professional air sampling costs roughly $300 to $600 for a basic assessment (two indoor samples plus one outdoor control, with laboratory analysis). Building biologists typically take additional samples in suspect areas (basement, HVAC system) and more samples in larger homes.

DIY air sampling kits are available for around $30 to $100 per sample, but they require careful use of the sampling pump and accurate results depend on proper technique. The laboratory analysis quality is also variable. If you suspect a significant mold problem, professional sampling gives more reliable results.

Tape lifts and swabs

If you can see a suspicious growth and want to identify whether it is mold (and what species), a tape lift or swab sample can be taken and analyzed. This does not tell you about airborne spore counts or the extent of contamination, but it confirms the presence and species of visible growth. Tape lift kits are available from laboratories for around $30 to $50 per sample including analysis.

ERMI testing

Environmental Relative Moldiness Index (ERMI) testing uses a dust sample collected from a settled surface (typically a vacuum sample from carpet or a flat surface) analyzed by quantitative PCR to detect the DNA of 36 mold species. It gives a single ERMI score that indicates the relative mold burden compared to a reference database of US homes. ERMI testing costs around $200 to $300 through commercial laboratories and is available as a DIY kit where you collect the dust sample and mail it in.

ERMI has limitations. It detects accumulated dust from months or years, not current conditions. It can reflect past mold problems that have been remediated. And the ERMI score is a relative index, not an absolute health standard. It is most useful as a screening tool to decide whether further investigation is warranted, not as a definitive assessment.

VOC Testing

Volatile organic compounds are gases emitted by paints, adhesives, flooring, furniture, cleaning products, and many other household materials. The list of VOCs in household air can include hundreds of compounds; the most commonly measured categories include total VOC burden (TVOC), specific compounds like benzene, toluene, xylene, and formaldehyde (sometimes tested separately).

Passive sampling

Passive VOC samplers are tubes containing absorbent material that you expose in your home for a set period (typically 24 to 72 hours), then mail to a laboratory for analysis. They measure average concentration over the sampling period. Costs range from $50 to $150 per sampler including laboratory analysis, depending on the number of compounds measured.

The analysis report will list compounds detected and their concentrations in micrograms per cubic meter (ug/m3). The WHO and various national agencies have published guideline values for specific VOCs. For total VOCs, a general guideline used in building biology practice is below 300 ug/m3 for normal comfort and below 100 ug/m3 for sensitive individuals.

Photoionization detector (PID) meters

PID meters measure total VOC concentration in real time using a UV light source. They are useful for identifying when VOC levels are elevated and for finding the sources (moving a PID meter near different materials shows which ones are off-gassing most). They do not identify specific compounds, and the reading depends on the calibration gas used, which may not match the VOC mix in your home. A PID meter reading of 0.5 to 1 ppm TVOC is a reasonable target for a well-ventilated occupied space.

When to test for VOCs

VOC testing is most useful in newly renovated or newly furnished spaces, in tightly sealed homes with limited ventilation, and for people with chemical sensitivities. New flooring, new furniture with composite wood components, new paint, and adhesives used during renovation all release VOCs that decline over time. Measuring at 1 week, 1 month, and 3 months post-renovation shows how quickly levels normalize.

Formaldehyde Testing

Formaldehyde is a specific VOC that deserves separate attention because of its prevalence in composite wood products (plywood, MDF, particleboard) and its classification as a known human carcinogen. It is present in most homes at some level; the question is whether the concentration is elevated enough to be a concern.

The WHO guideline for indoor formaldehyde is 0.08 ppm (80 ppb) as a 30-minute average, with some agencies recommending lower targets for long-term exposure. New furniture, cabinetry, and flooring made with adhesives that use urea-formaldehyde (UF) resin can release formaldehyde at elevated rates for months to years after installation.

Testing options

Passive formaldehyde badges are available for around $20 to $50, including laboratory analysis. You expose the badge in the room of concern for a specified period and mail it to the lab. The result is an average concentration over the exposure period. These are the most accessible way to get a baseline formaldehyde reading.

Electrochemical formaldehyde monitors ($50 to $200) give real-time readings and are useful for tracking how levels change with ventilation, temperature, and humidity. Higher temperature and humidity accelerate formaldehyde off-gassing from composite wood. Readings in winter (tighter sealing, lower ventilation) will typically be higher than in summer.

Radon Testing

Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. It seeps into buildings through foundation cracks, slab penetrations, and soil contact. It is the second leading cause of lung cancer after smoking in the US, and unlike most indoor air quality issues, the evidence linking radon to lung cancer is strong and uncontested.

The EPA action level for radon is 4 pCi/L (picocuries per liter). The EPA recommends considering mitigation at 2 to 4 pCi/L. Building biology practitioners typically recommend mitigation at 2 pCi/L or above. Radon levels vary by geography, by season, and between individual houses on the same street.

DIY radon test kits

Short-term radon test kits (alpha track detectors or activated charcoal canisters) are available for $10 to $30, including laboratory analysis, from hardware stores and online retailers. You place the detector in the lowest occupied level of your home for 2 to 7 days, then mail it to the laboratory. Short-term tests give a result quickly but can be affected by weather conditions during the test period.

Long-term radon monitors (alpha track detectors left in place for 90 days to one year) give a more accurate average that is less affected by short-term weather fluctuations. Costs are similar. A long-term test is more reliable for deciding whether mitigation is needed.

Electronic radon monitors (CairSens, Airthings, Ecosense) give continuous real-time readings and are useful for tracking seasonal variation and confirming whether mitigation has worked. Costs range from $100 to $250.

Carbon Dioxide and Ventilation

Carbon dioxide (CO2) is not toxic at typical indoor concentrations, but elevated CO2 is a reliable indicator of inadequate ventilation. High CO2 levels mean that other indoor pollutants (VOCs, mold spores, particulates from occupants) are also accumulating because fresh air exchange is insufficient.

Outdoor CO2 is approximately 420 ppm. Indoor CO2 in a well-ventilated space with normal occupancy should be below 1000 ppm. Above 1000 ppm, cognitive performance begins to decline measurably. Above 2000 ppm, occupants often experience headaches, fatigue, and difficulty concentrating. In tightly sealed modern homes with multiple occupants and limited ventilation, CO2 can reach 2000 to 3000 ppm in bedrooms overnight.

CO2 monitors

Consumer CO2 monitors are now widely available for $50 to $150. Models from Aranet, Airthings, and CO2Meter are reliable and accurate. A CO2 monitor in a bedroom overnight shows whether ventilation is adequate. If readings exceed 1000 ppm, increasing ventilation (opening a window slightly, adjusting HVAC settings, or adding a mechanical ventilation unit) will improve air quality broadly, not just CO2 levels. See the ventilation guide for how to improve fresh air exchange without increasing EMF exposure from HVAC equipment.

Particulate Matter

Fine particulate matter (PM2.5 and PM10) in indoor air comes from cooking, candles, incense, tobacco smoke, tracked-in particles, and in some cases from outdoor air infiltration during high-pollution periods. PM2.5 (particles under 2.5 micrometers) penetrates deepest into the lungs and is the most relevant for health.

The WHO guideline for annual mean PM2.5 is 5 ug/m3. Cooking a meal on a gas stove can spike indoor PM2.5 to hundreds of ug/m3 briefly. Burning candles or incense can do the same. These spikes are transient and clear with ventilation.

Consumer air quality monitors that include PM2.5 sensors (Airthings, PurpleAir, IQAir AirVisual) cost $100 to $300 and give real-time and logged particulate readings. They are useful for identifying sources (cooking, candles, guests who smoke outside coming back in) and for confirming that ventilation is clearing spikes adequately.

Professional Indoor Air Quality Assessment

A professional indoor air quality assessment by a building biologist or industrial hygienist includes sampling for multiple pollutants, visual inspection of moisture-prone areas, HVAC system inspection, and a comprehensive written report with recommendations. Costs range from $500 to $2,000 or more depending on the scope and the size of the home.

A building biology assessment combines IAQ testing with EMF assessment and often includes recommendations for both air quality and electromagnetic environment. This is relevant if you want a holistic assessment of your home's indoor environment rather than testing isolated parameters. See the EMF assessment guide for what a full building biology assessment covers.

Frequently Asked Questions

What indoor air quality test should I start with?

Start with radon if you have not tested before, particularly if you have a basement or live in a high-radon area. It is inexpensive, important, and often overlooked. If you have had any water intrusion or see any signs of moisture damage, add mold sampling. If you have recently renovated or installed new furniture, add a VOC or formaldehyde test. CO2 monitoring is cheap and tells you whether your ventilation is adequate for everything else.

How do I find a reliable IAQ testing professional?

Look for a certified industrial hygienist (CIH), a certified indoor environmentalist (CIE), or an IBE-certified building biologist. Avoid contractors who both test and remediate, since this creates an incentive to find problems. Ideally, use separate professionals for testing and for any remediation work. Check the building biologist directory for certified practitioners in your area.

How quickly do VOCs from new furniture go away?

Off-gassing rates depend on the material, temperature, and ventilation. Most VOC-emitting materials release the majority of their volatile compounds within the first 3 to 6 months. Maximizing ventilation (open windows, run HVAC fan) during this period accelerates the process. Higher temperatures speed off-gassing, so ventilating during warmer days is particularly effective. Formaldehyde from composite wood may continue at detectable levels for 1 to 2 years.

Are home air quality monitors accurate?

Consumer monitors for CO2 (Aranet4, Airthings) and PM2.5 (PurpleAir) are reasonably accurate for relative measurement and trend tracking. They are not laboratory-grade instruments and should not be relied on for precise compliance measurements. For VOCs and formaldehyde, consumer sensors are far less reliable. Use laboratory-analyzed passive samplers for those parameters if you need accurate results.