Testing your air quality starts with knowing what you’re looking for. Some pollutants, like radon and carbon monoxide, require specific detectors. Others, like fine particulate matter and volatile organic compounds (VOCs), can be tracked with consumer-grade monitors. The best approach depends on whether you’re checking outdoor conditions, investigating a problem inside your home, or establishing a baseline before renovations.
Signs You Should Test Your Indoor Air
Poor indoor air quality doesn’t always announce itself with a smell. Headaches, eye irritation, dry cough, dizziness, nausea, fatigue, and difficulty concentrating are all associated with what the EPA calls “sick building syndrome.” If these symptoms improve when you leave the building and return when you come back, the air is a likely culprit. More serious signs, like chest tightness, fever, chills, and muscle aches, can point to biological contamination from mold or bacteria.
Beyond symptoms, certain situations call for testing even if you feel fine. You just moved into an older home. You’re planning a renovation that could disturb lead paint or asbestos. You’ve had water damage lasting more than 24 to 48 hours. You’ve noticed persistent musty odors. Or you simply want a baseline reading of what you’re breathing every day.
What Pollutants to Test For
The EPA identifies several major indoor pollutants, and each requires a different testing approach:
- Radon: A radioactive gas that seeps up from soil. It’s the second leading cause of lung cancer and is completely odorless. Every home should be tested at least once.
- Particulate matter (PM2.5): Tiny particles from cooking, candles, wood stoves, and outdoor pollution that penetrate deep into the lungs. The EPA’s current health-based annual standard is 9.0 micrograms per cubic meter.
- Carbon monoxide (CO): A deadly, odorless gas produced by furnaces, gas stoves, and fireplaces.
- VOCs: Gases released by paint, cleaning products, new furniture, and building materials. Formaldehyde is one of the most common.
- Mold spores: Thrive in damp areas and cause respiratory symptoms and allergic reactions.
- Carbon dioxide (CO2): Not toxic at normal levels, but elevated CO2 signals poor ventilation. Research from Harvard’s School of Public Health found that for every 500 ppm increase in CO2, response times slowed by 1.4 to 1.8 percent, with no lower threshold identified where the effect disappeared.
- Nitrogen dioxide (NO2): Produced by gas stoves and space heaters.
DIY Testing Options
For radon, a simple mail-in test kit is the standard starting point and costs under $20 at most hardware stores. Short-term kits measure radon levels over 2 to 90 days. Long-term kits run for more than 90 days and give a more accurate picture of your average exposure. Place the device in your basement or the lowest livable level of your home, at least three feet off the ground, in the middle of the room. If you live in an apartment or condo, place it on the lowest floor of your unit.
Consumer air quality monitors can track PM2.5, VOCs, CO2, temperature, and humidity in real time. Devices from brands like Aranet, IQAir, and Awair range from $80 to $300 and connect to smartphone apps that log trends over time. These are useful for identifying patterns: whether cooking spikes particle levels, whether your bedroom CO2 climbs overnight because of poor ventilation, or whether a new piece of furniture is off-gassing VOCs.
Carbon monoxide detectors are inexpensive and should already be installed on every floor of your home. They’re not optional testing equipment; they’re safety devices. If you don’t have them, install them before anything else.
Why DIY Mold Tests Fall Short
Drugstore mold test kits use settling plates, small dishes with a growth medium that you leave open in a room. These only capture spores that happen to drift down and land on the plate, which represents a tiny fraction of what’s actually in the air. More importantly, they lack an outdoor control sample. Professional mold inspectors always take an outdoor reading to establish a baseline, because what looks like a “high” indoor count might actually be lower than outdoor levels (indicating a healthy environment), while a seemingly “low” count could signal a serious problem when compared to normal outdoor air. Without that comparison, DIY mold results are essentially uninterpretable.
When to Hire a Professional
Professional indoor air quality testing typically costs between $292 and $586, with an average around $439. Thorough assessments can run up to $1,000 depending on your home’s size and the number of pollutants tested. That price gets you calibrated equipment, lab analysis, and a detailed report.
Professional testing uses tools that consumer devices can’t match. For mold, inspectors draw air through a calibrated pump at 15 liters per minute, trapping spores on a collection medium that a lab then counts under a microscope. This gives you actual spore concentrations you can compare against outdoor baselines.
Certain situations specifically require professional documentation. Insurance companies often deny claims based on DIY testing because they need certified assessments following established protocols. Legal matters and real estate transactions demand the same level of rigor. Home sellers who rely on DIY tests for disclosure can face liability if a professional inspection later reveals problems the kit missed.
Checking Outdoor Air Quality
Outdoor air quality is measured using the Air Quality Index (AQI), a scale from 0 to 500 maintained by the EPA. You can check your local AQI in real time at AirNow.gov or through weather apps.
The AQI breaks down into six color-coded categories:
- Green (0 to 50): Good. Air pollution poses little or no risk.
- Yellow (51 to 100): Moderate. Acceptable for most people, though unusually sensitive individuals may notice effects.
- Orange (101 to 150): Unhealthy for sensitive groups, including people with asthma, heart disease, or lung conditions.
- Red (151 to 200): Unhealthy. Some members of the general public may experience effects.
- Purple (201 to 300): Very unhealthy. Health risk is increased for everyone.
- Maroon (301+): Hazardous. Emergency conditions affecting the entire population.
The AQI tracks five major pollutants: ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide. The number you see reported is based on whichever pollutant is highest that day. During wildfire season, PM2.5 usually drives the number. On hot summer days, ozone is more commonly the culprit.
If you want hyper-local outdoor readings rather than regional averages, low-cost PM2.5 sensors like those from PurpleAir create a network of community monitors. These are particularly useful if you live near a highway, industrial facility, or in an area prone to wildfire smoke, where conditions can vary significantly from the nearest government monitoring station.
Making Sense of Your Results
A single reading rarely tells the full story. Air quality fluctuates throughout the day based on cooking, cleaning, ventilation, weather, and traffic patterns. If you’re using a consumer monitor, track readings over at least a week before drawing conclusions. Note what activities correspond to spikes.
For radon, the EPA recommends taking action if your result is 4 picocuries per liter (pCi/L) or higher. If a short-term test comes back elevated, follow up with a long-term test to confirm. Radon mitigation systems, which vent the gas from beneath your foundation to outside, typically bring levels down by 80 to 99 percent.
For PM2.5, keep indoor levels below the EPA’s annual standard of 9.0 micrograms per cubic meter when possible. Running a HEPA air purifier, improving ventilation, and avoiding indoor combustion sources (candles, incense, wood fires) are the most effective ways to lower particle counts. CO2 levels above 1,000 ppm generally indicate your space needs more fresh air. Opening windows, running exhaust fans, or adjusting your HVAC system’s outdoor air intake can bring those numbers down quickly.