Straight Answer
How Often Should You Test for Radon?
The short version. How often should you test for radon? The honest, two-part answer: about every two years for a house nothing's changed on, and sooner any time something big happens to the house (renovation, new HVAC, foundation work, finishing a basement, encapsulating a crawlspace, a mitigation install, or a home sale). One "low" reading doesn't settle the question forever — radon levels drift with the ground, the house, and the seasons.
The rest of this page walks through when a re-test is worth doing and when it isn't.
2years
EPA baseline re-test cadence
4.0pCi/L
EPA action level
48hrs
minimum re-test time
Every Two Years
The Baseline: About Every Two Years
For a house where nothing has visibly changed — same foundation, same HVAC, same dirt sloped around the house, no additions, no basement finish-out — EPA says re-test about every two years. That's a conservative interval that reflects the reality that radon is a soil gas whose level inside your house depends on lots of small things that shift over time: how tightly the foundation is sealed, how the ground around the house drains, how your HVAC cycles, and how the house itself is settling into its lot.
Two years isn't a hard rule. It's a floor that assumes nothing about the house has moved. The moment something does move, the clock restarts. That's the second half of the answer, next.
What Resets The Clock
Events That Reset the Re-Test Clock
Any of these is a good reason to re-test sooner than every two years, no matter what your last result was:
- Renovation or addition. New rooms, structural work, or any project that changes the shape or envelope of the house can change how it exchanges air with the soil beneath it.
- New HVAC system or major HVAC change. Replacement units, added zones, new ductwork, and whole-house dehumidifiers all shift the pressure dynamics of the house. A different HVAC system pulls soil gas differently.
- Foundation work. Crack sealing, waterproofing, sub-slab drainage, pier work, or basement wall repair — any of these can change how radon enters, in either direction.
- Finishing a basement. Turning storage into living space raises the effective exposure the same reading produces, because more hours are being spent at the level where radon is highest.
- Converting a basement into a bedroom. The highest-value re-test on this list. A bedroom is where a person spends the most continuous hours per day; a basement bedroom compounds that with the level of the house where radon concentrates.
- Encapsulating a crawlspace. Encapsulation removes the passive ventilation that used to dilute radon underneath the floor. Test before and after, even if the house has never registered a problem.
- Post-mitigation. After a mitigation system is installed, the EPA recommends a confirming test to verify the system works, and periodic re-testing after that to confirm it keeps working. Mitigation fans have a lifespan measured in years, not decades.
- Buying or selling. A radon test during the inspection contingency is standard for a reason — the buyer needs a number, and the seller wants a defensible one on record. See our page for agents for how that timeline typically works.
Why Seasons Matter
Why the Season the Test Ran In Matters
Radon usually reads higher in winter. Two reasons: the house is closed up more of the day for heating, and warm air rising inside the house pulls a stronger vacuum down at the foundation, which pulls more soil gas up through cracks and pipe penetrations. A summer reading and a winter reading in the exact same house can differ by 30% or more.
What that means for you: a summer "pass" isn't a full-year answer. A summer result of 2.8 pCi/L in the metro can easily correspond to a winter reading over 4.0 pCi/L in the same house, with nothing about the house having changed in between. A long-term alpha-track detector (the kind that sits for 90 days to a year) is the closest a homeowner can get to a real yearly average, exactly because it covers the range of conditions your house actually sees.
If a short-term test ran in summer and came back between 2 and 4 pCi/L, the honest next step is a confirming test in a cooler month — seewhat to do with a 2 to 4 pCi/L result for the full decision.
After A Mitigation System
Re-Testing After a Mitigation System
A mitigation system isn't set-and-forget. The common design (called "sub-slab depressurization" — a fan and pipe that pulls the soil gas out from under your house and vents it above the roof) uses a small in-line fan that has a working life measured in years, not decades. There's a little U-shaped gauge on the pipe (called a manometer) that shows the fan is moving air — but that only confirms the fan is running. It doesn't tell you what your actual indoor radon number is.
EPA recommends a confirming test within 30 days of the install (to prove the system worked), and periodic re-tests after that on a two-year cycle. If the fan ever gets replaced or serviced, add a confirming test on top of the regular cycle. For more on the mitigation side, see fixing radon.
Why It Matters Here
Why the Re-Test Cadence Matters in the Birmingham Metro
Jefferson and Shelby counties both sit on the Alabama Department of Public Health's list of the 15 highest-potential radon counties. In the CDC's 2008–2017 data, about 1 in 9 reported tests in each came back at or above 4.0 pCi/L (the level where EPA says to fix your home). This isn't a low-radon area where a single "all clear" test settles the question forever. In a metro that averages 1.9 pCi/L at the county level — and where individual readings have hit 24.6 pCi/L (Jefferson) — a periodic re-test is real cost-benefit math, not a formality.
A professional re-test in the metro is $295 flat, same as the original — sealed monitor, 48-hour minimum, independent lab reading. Seehow the test itself works,the DIY and pro steps, andhow long the full process takes.
Time for a two-year re-test? $295 flat, metro-wide.
FAQ
Frequently Asked Questions
How often should I test my home for radon?
Roughly every two years for a home nothing has changed on. The EPA recommends re-testing on a two-year cadence even when the house has been sitting undisturbed, because radon levels drift as soil conditions, foundation cracks, and grading shift. Test more often than that when something meaningful about the house has changed — renovation, HVAC replacement, foundation work, finishing a basement, encapsulating a crawlspace, or a mitigation system installed or serviced.
Do I need to test again if my last result was low?
Yes, on a longer cycle. A low reading confirms the house was low during that test window, not permanently. Radon concentrations shift with soil settling, seasonal weather patterns, small cracks that open over time, and any change to how the house exchanges air with the ground underneath it. A previous low reading raises the odds the next one is low too — it does not close the question forever.
Should I test after finishing my basement or adding a bedroom downstairs?
Yes — and this is one of the highest-value re-tests a homeowner can run. Finishing a basement or converting a lower-level room into a bedroom raises the effective radon exposure of the same reading, because more hours are being spent at the level of the home where radon is highest. Test before the project (baseline), and test after the project (new steady state), even if a prior test came back well below 4.0 pCi/L.
Does the time of year matter for radon testing?
Yes. Radon typically reads higher in winter, when the house is closed up and the stack effect pulls more soil gas in through the foundation. A summer result at 2.8 pCi/L can easily correspond to a winter reading above 4.0 in the same house. For that reason, a summer 'pass' is not the same as a full-year answer, and a long-term alpha-track detector run for 90 days or more is the most honest way to average across the seasons a house actually sees.