How often should you test radon levels?
Updated July 2026
Retest your home's radon every 2 years, and again after any major renovation, foundation work, or HVAC change that alters how air moves through the house. This holds even if you already have a mitigation system, because the fan can fail without any alarm. Radon is an invisible, odorless gas that seeps up from the soil, and the EPA sets an action level of 4.0 pCi/L, so a $15–40 test kit is the only way to know where you actually stand.
What changes the interval
| Your situation | Interval | Why |
|---|---|---|
| Home has never been tested | Test now | Radon has no smell or color; a first test is the only way to find a hidden problem |
| Routine retest, no changes | Every 2 years | Levels drift as soil, weather, and the house settle over time |
| After a major renovation or addition | Retest after work | New cracks and airflow paths can raise radon that was fine before |
| After new HVAC or heavy air sealing | Retest | Changing house pressure changes how much radon is pulled up from below |
| Mitigation system already installed | Every 2 years, plus after fan work | A silent fan failure lets levels climb back; only a test confirms it |
| Buying or selling the home | Test during inspection | A short-term test is standard in the transaction and drives repairs |
| Result between 2 and 4 pCi/L | Retest and consider action | The EPA says fix at 4.0 and consider mitigation in the 2 to 4 range |
The cost of skipping it
What skipping it costs: radon is the second-leading cause of lung cancer in the US and the leading cause among people who never smoked, per the EPA. The danger is that it builds up for years with zero warning signs, so an untested home, or one whose mitigation fan quietly died, exposes a family the whole time. A test kit is $15–40 and a continuous monitor is $150–250, while a mitigation system, if you need one, runs roughly $800–2,500. The cost of not knowing is measured in health, not dollars.
How to do it (Set up in 10 minutes · DIY test kit)
- Buy a short-term charcoal kit or a reusable continuous radon monitor; the kit price usually includes the lab fee.
- Place it in the lowest lived-in level of the home, 2 to 3 feet off the floor, away from drafts, vents, and exterior walls.
- Keep windows and exterior doors closed for 12 hours before and during a short-term test (closed-house conditions).
- Leave a short-term kit in place 2 to 7 days, or a long-term kit 90 days or more for a truer yearly average.
- Mail the kit to the lab or read the monitor, then compare the result to the 4.0 pCi/L action level.
- If the reading is elevated, run a second confirming test before committing to a mitigation system.
Knowing the interval is the easy half. OnOtto reminds you at the right interval, and it won't let you snooze it into next year. Tasks persist until they're done, and completing radon tests schedules the next one automatically.
Put this on autopilot, free for 30 daysFrequently asked questions
What radon level is dangerous?
The EPA sets its action level at 4.0 pCi/L: at or above that, you should install mitigation. Between 2 and 4 pCi/L, the agency suggests considering it, since no amount of radon is truly risk-free and the average outdoor level is only about 0.4 pCi/L. The higher the number and the more hours people spend on that level of the house, the more it matters. One elevated reading is worth confirming with a second test before you spend on a fix.
Do I still need to test if I have a radon mitigation system?
Yes, and arguably more often. Mitigation fans run 24/7 and fail without any alarm, so a system that stopped working months ago can let radon creep right back to its old level. Retest every 2 years and after any fan replacement or service, and pair that with a monthly glance at the pipe's manometer gauge to confirm the fan is still pulling suction. The gauge shows airflow; only a test shows the actual radon number.
What's the difference between a short-term and long-term radon test?
A short-term test sits for 2 to 7 days and gives a fast screening snapshot, which is why it is used in home sales. A long-term test runs 90 days or more and captures a truer average, because radon swings with weather, season, and how much the house is sealed up. Winter readings often run higher than summer. A sensible approach: screen with a short-term kit, and if it is borderline or elevated, confirm with a long-term test.
Is a DIY radon kit as accurate as a professional test?
For screening, a quality lab-analyzed kit is reliable and cheap at $15–40. The catches are placement and honesty of conditions: a poorly located kit or an open window skews the result. Real estate transactions sometimes require a certified tester using a tamper-resistant continuous device, so the seller cannot influence the reading. If you want ongoing peace of mind rather than a one-time number, a $150–250 continuous monitor gives a live reading you can watch year-round.