How to Test Your Home for Radon
A short-term test (2-90 days) gives a fast snapshot; a long-term test (over 90 days) accounts for seasonal variation and gives a more reliable picture. DIY kits sold at hardware stores are a reasonable first step; a result at or above 4 pCi/L on either type is when mitigation planning starts.
Short-term vs. long-term
Radon levels fluctuate with weather, season, and how a house is used (windows open vs. closed, HVAC running or not). A short-term test is faster and cheaper but more sensitive to whatever conditions happened during that window. A long-term test smooths that out and is considered more representative of year-round average exposure. Real estate transactions almost always use a short-term test because of closing timelines; a homeowner with no deadline gets a more accurate picture from a long-term test.
DIY kits vs. professional testing
Charcoal-canister DIY kits, available at most hardware stores for $15-30, are a legitimate, EPA-recognized method for an initial short-term test. A professional test with continuous radon monitoring equipment costs more ($150-700, per our cost guide) but is standard for real estate transactions and gives real-time data rather than a single averaged number.
How to actually run a DIY test
- Place the kit in the lowest lived-in level of the home (a finished basement counts; an unfinished crawlspace used only for storage does not)
- Keep windows and exterior doors closed as much as normal during the test period
- Avoid running the kit during unusually high winds or right after a big weather change, which can skew a short-term result
- Mail the kit to the lab promptly once the test period ends; a delayed mail-in affects accuracy
What your number means
Below 2 pCi/L: generally low priority. Between 2 and 4 pCi/L: worth considering mitigation, especially for a long-term result. At or above 4 pCi/L: the EPA's standard action level, mitigation recommended. See our radon and health guide for why there's no fully "safe" number, just a practical threshold.