How to Test Air in House | The Radon-First Checklist

Testing the air in your house starts with radon, the only pollutant that requires a dedicated test kit to detect.

Most homeowners assume the air inside their house is fine until something smells wrong or someone gets sick. But the pollutant that matters most — radon — is odorless and invisible, so you cannot rely on your senses. The Environmental Protection Agency (EPA) and the Consumer Product Safety Commission (CPSC) both agree that testing for radon is the single most important air-quality check you can do at home. Here is the order that actually works.

Why Radon Is The First Test

Radon is a radioactive gas that seeps into homes through cracks in the foundation, and it is the leading cause of lung cancer among non-smokers. Because it has no smell, no color, and no immediate symptoms, the CPSC says measurement is the only way to know whether it is present.

The EPA goes further: testing is the only way to know whether radon is present, and every home in the United States should be tested — even if you have tested before. If you have not tested the basement specifically, the EPA recommends testing again, because that lowest level is where radon concentrations are typically highest.

How To Run The Test Yourself

Testing for radon is a straightforward process that takes about 48 hours. The steps below follow the official guidance from the EPA and CPSC.

1. Choose the lowest lived-in level. The EPA specifies the lowest lived-in area — a basement you use regularly or a first floor if you never go downstairs. Place the test there.
2. Buy a certified test kit. The CPSC says to choose a do-it-yourself kit that displays “Meets EPA Requirements” on the package, or a state-certified kit. Kits typically cost $15–$30 and are sold at hardware stores and online.
3. Close windows and doors. For accurate results, keep the house closed up for at least 12 hours before and during the test, per the kit’s instructions.
4. Place the test at breathing height. Set the kit in the middle of the room, away from drafts, exterior walls, and heat sources.
5. Mail the test to the lab. After the test period ends, seal the kit and send it to the listed laboratory. Results arrive in about a week.

Hiring a trained professional is a valid alternative, and the CPSC says it is worth considering when you are buying or selling a house. A contractor’s test is faster and eliminates the margin for user error, but it costs more — typically $150–$300.

What The Results Tell You

The EPA has set a clear action threshold: if your radon level is 4 picocuries per liter (pCi/L) or higher, fix the home. Levels below 4 pCi/L still carry some risk, and the CPSC notes that reducing levels even below that threshold is worth considering. If you decide to fix the problem, the usual solution is a vent pipe and fan system that pulls radon from beneath the house and exhausts it outside.

When a radon test comes back high, fix the problem and then retest after the mitigation system is installed to confirm it works.

Beyond Radon: Smoke, Carbon Monoxide, And Air Quality Monitors

While radon needs a specialized test kit, the other essential air checks use alarms. The EPA says every home should have carbon monoxide and smoke alarms installed and working — they are the earliest warning of combustion problems and fire. Carbon monoxide is also colorless and odorless, so detection is the only defense. If you are buying an air tester for home, look for a unit that combines these checks with a particulate sensor to cover the basics.

For broader indoor air quality, the EPA cautions that low-cost air pollution monitors are not generally evaluated by the agency under indoor test conditions, so treat their results cautiously. These devices can indicate trends — higher particulate levels when cooking, for example — but they are not certified diagnostic instruments. Visible mold and humidity problems are best addressed by finding the moisture source, not by measuring the air.

If you are ready to buy a device, our tested roundup of the best air testers for home use compares certified radon kits, combination monitors, and professional-grade meters side by side.

You do not need a lab to test the air in your house — you need a $20 radon kit and a working carbon monoxide alarm. Run the radon test in the lowest lived-in level, act on the number, and treat any consumer monitor readings as a trend rather than a verdict.