Why “Indoor Air Quality Testing” Is Really Several Different Tests
There is no single instrument that measures everything that can be wrong with indoor air. The EPA's indoor air quality program groups the main concerns into combustion gases (carbon monoxide, nitrogen dioxide), particles, radon, volatile organic compounds, biological contaminants (mold, dust mites, pet dander) and moisture. Each is detected with a different method, and each has a different threshold for action. Searching for “indoor air quality testing near me” usually turns up firms that sample some of these and not others, so it pays to know what you actually need before you call.
Step 1: Radon and Carbon Monoxide (Do These First)
These two pollutants deserve dedicated tests because the stakes are highest and the tests are cheap. Radon is a radioactive gas from soil that the EPA identifies as the leading cause of lung cancer among non-smokers. The EPA's radon guidance recommends testing every home and fixing it at or above 4 pCi/L; short-term charcoal kits cost little and continuous digital monitors show day-to-day swings. Our radon monitor vs. test kit guide compares the two approaches.
Carbon monoxide comes from any fuel-burning appliance, a vehicle in an attached garage, or a blocked flue. It is not reliably measured by general-purpose indoor air quality monitors. The EPA's carbon monoxide page recommends a CO alarm that meets the UL 2034 standard, installed near sleeping areas on every level. If you already have alarms, check their date: most sensors expire after 7 to 10 years.
Step 2: A Consumer Monitor for Particles, CO2, VOCs and Humidity
A tabletop indoor air quality monitor answers the questions most people are actually asking: is the air in this room dusty or smoky, is it stuffy, and is it too damp? Look for a laser-scattering PM2.5 sensor and a non-dispersive infrared (NDIR) CO2 sensor; models that estimate CO2 from a VOC sensor are not reliable. Run it for at least a week, moving it between the bedroom, kitchen and living room, and watch for patterns rather than single readings.
| Reading | Reference level | Source | What a high reading usually means |
|---|---|---|---|
| PM2.5 | 35 µg/m³ (24-hr), 9 µg/m³ (annual) | EPA NAAQS | Cooking, smoke infiltration, candles, dust; undersized or absent filtration |
| CO2 | ~1,000 ppm as a ventilation guide | Common industry guidance | Too many people for the air exchange; closed-up room |
| Relative humidity | 30% to 50% | EPA mold guidance | Mold and dust-mite risk above 60%; dry-air irritation below 30% |
| TVOC | No federal standard; watch trend | EPA | Cleaning products, paint, new furniture, fragrances |
| Radon | 4 pCi/L action level | EPA | Soil gas entry through slab, sump, crawl space |
| Carbon monoxide | Any alarm activation | UL 2034 | Faulty furnace, water heater, generator, vehicle exhaust |
The PM2.5 reference levels are the EPA's National Ambient Air Quality Standards, written for outdoor air; there is no federal indoor standard, but they are the most defensible benchmark. For humidity, the EPA's mold guidance recommends keeping indoor relative humidity below 60%, ideally 30% to 50%. If you want a deeper look at what these devices can and cannot detect, read Do You Need an Indoor Air Quality Monitor?
Step 3: When to Hire a Professional
Professional testing makes sense when the suspected problem cannot be measured by a consumer device or when the result has legal or medical weight. Typical cases:
- Mold. Visible growth does not need a test; fix the moisture and remove it. Hidden mold behind walls or after a flood may justify a certified inspector who takes air and surface samples for lab analysis. The EPA notes that sampling is unnecessary in most cases and that there are no federal limits for mold spores in air.
- Asbestos and lead paint. Required before renovating older homes; must be sampled by an accredited inspector and analyzed by a lab.
- Formaldehyde or specific VOCs. After new cabinetry, flooring or a strong persistent odor, a lab-analyzed passive sampler identifies the specific compound.
- Unexplained symptoms. Headaches, nausea or respiratory irritation that improve when you leave the house warrant a professional walk-through that includes combustion appliance safety testing.
Ask any firm what they will sample, which lab they use, and what standard they will compare results against. A report full of numbers with no reference levels is not worth paying for.