Testing for Radon: How to Find Out What's in Your Home's Air
Radon can’t be seen or smelled — but it’s remarkably easy to measure. And because levels differ drastically even between neighboring houses, only your own test gives you a real answer.
Two ways to test
1. Passive test kits (the classic route). Small charcoal canisters or alpha-track detectors without any electronics — you simply place them in a room. After the test period you mail them to a lab and receive a report. Short-term kits cost about $15–40 including lab analysis; many U.S. state radon programs even hand them out free during January’s National Radon Action Month. For results that count in a real estate transaction, hire a certified professional (NRPP or NRSB listed).
2. Digital monitors (the ongoing view). Electronic devices show the level continuously, often with an app. They’re great for watching short-term swings or verifying that mitigation works — but they don’t replace a proper long-term measurement.
When and where to test
- Test in the heating season: closed windows and running heat drive levels up — that’s exactly when a measurement is meaningful.
- Short-term first, long-term for certainty: a 2–7 day charcoal test gives a first answer; a 3–12 month alpha-track test captures the annual average that actually matters.
- Test the lowest lived-in level: the bedroom or family room in the basement or on the ground floor — not the unused corner of a crawl space.
- Live normally: heat and ventilate as usual during the test — otherwise you measure a scenario that has nothing to do with your life.
Reading the result
| Result (annual average) | What it means |
|---|---|
| below 2 pCi/L (~75 Bq/m³) | Unremarkable — the WHO target of 100 Bq/m³ is in this range |
| 2–4 pCi/L | EPA says: consider fixing; simple measures like better ventilation are worthwhile |
| 4 pCi/L (148 Bq/m³) and up | EPA action level exceeded — fix your home, see Reducing radon |
A single high day on a digital monitor is not an alarm, by the way: after an unventilated weekend or in certain weather, readings spike and fall again. The annual average is what counts.