Garden 
Affiliate Disclosure
Some links on this page are affiliate links. As an Amazon Associate, we earn from qualifying purchases — at no extra cost to you. We do not buy, test, or physically handle the products we cover; our rankings come from aggregated owner reviews, ratings and expert consensus. Commissions never change our verdicts. How we rank · full disclosure.
To test for radon, run a short-term charcoal or alpha-track kit for 2 to 7 days, or set up a continuous digital monitor, on the lowest lived-in level of your home with the windows closed. The EPA action level is 4 picocuries per liter (pCi/L): at or above that, you should mitigate. A DIY kit costs about 15 to 40 dollars, a reusable monitor 130 to 250 dollars, and results are reliable when you place the detector correctly and keep the house closed up during the test.
Radon is a colorless, odorless radioactive gas that seeps up from soil into homes, and it is the second leading cause of lung cancer in the U.S. after smoking, per the EPA and the Surgeon General. Because it is invisible, testing is the only way to know your exposure. We do not test products first-hand; our picks come from aggregated owner reviews and expert consensus, described in how we rank.
The three ways to test for radon
Each method trades speed for accuracy. Most people start fast and confirm slow.
| Method | Duration | Typical cost | Best for |
|---|---|---|---|
| Short-term kit (charcoal/alpha-track) | 2 to 7 days | $15 to $40 | Fast first screen |
| Long-term kit (alpha-track) | 90 days to 1 year | $25 to $60 | True annual average |
| Continuous digital monitor | 48 hrs to ongoing | $130 to $250 | Ongoing tracking |
Short-term kits are mailed to a lab after exposure; the fee usually includes lab analysis, but check, because some list the lab fee separately. Continuous monitors give a running average on a screen or app with no lab step, which is why they have become the choice for people who want to watch levels over time rather than get one snapshot. For the ranked field see best radon test kits.
How to run a short-term test, step by step
- Pick the room. Use the lowest level you occupy regularly — a finished basement, or the ground floor if you have no basement. Choose a room people actually use, not a closet or crawlspace.
- Close the house 12 hours before. Keep windows and exterior doors shut, opening them only to come and go. This gives the reading that reflects normal closed-house conditions.
- Position the detector. Place it 2 to 6 feet above the floor, at least 3 feet from windows and exterior doors, and away from drafts, heat, direct sun and high humidity.
- Do not disturb it. Leave it in place for the full test window listed on the kit, typically 2 to 7 days. Do not move it, cover it, or turn on strong fans nearby.
- Send it in promptly. Charcoal kits must reach the lab quickly because charcoal keeps adsorbing and the reading degrades. Fill in the start and stop times and mail it the same day you finish.
Avoid testing during unusual weather — a major storm or high winds can skew a short-term result — and avoid the peak of a severe cold snap if you can, since heating patterns change how the house draws air.
What the numbers mean
Radon is measured in picocuries per liter of air (pCi/L). The EPA guidance is straightforward.
| Reading | What it means | Action |
|---|---|---|
| Below 2 pCi/L | Low | Retest every few years |
| 2 to 3.9 pCi/L | Elevated but below action level | Consider mitigation; the EPA says fixes should be weighed here |
| 4 pCi/L and above | At or above EPA action level | Confirm with a second test, then mitigate |
The EPA is explicit that there is no risk-free level of radon, and that the average indoor level in the U.S. is about 1.3 pCi/L. A single high short-term reading should be confirmed with a second short-term test or a long-term test before you spend on mitigation, because levels fluctuate day to day.
When and how often to test for radon
Radon is not a one-and-done check.
- Test every home, once, at minimum. The EPA recommends every home be tested regardless of ZIP code or a neighbor's result.
- Retest every 2 to 5 years in your own home, and after any major renovation, foundation work, or a change in how you use the basement.
- Test in winter if you can. Levels tend to run higher when the house is closed up and the heating system is drawing air, so a cold-season test is a conservative check.
- Always test during a home purchase. A radon test is standard in many U.S. real estate transactions, and a professional or tamper-resistant test is worth it there.
What to do if the level is high
An elevated result is fixable, and mitigation is well understood. The standard fix is sub-slab depressurization: a certified contractor installs a vent pipe and a continuously running fan that pulls radon from beneath the foundation and exhausts it above the roofline before it can enter the home.
| Item | Typical range (U.S., 2026) |
|---|---|
| Professional mitigation system | $800 to $2,500 |
| Post-mitigation confirmation test | $25 to $150 |
| Annual fan electricity | $50 to $150 |
These are national ranges as of early 2026; actual costs vary with home size, foundation type and region, so get local quotes. Radon mitigation contractors are certified through programs like the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB); many states list qualified professionals, and local codes and licensing requirements differ, so check your state radon office. After mitigation, always run a follow-up test to confirm the system dropped you below 4 pCi/L.
Common radon testing mistakes
Most bad radon readings come from procedure errors, not faulty kits.
- Opening windows during the test. This dilutes the reading and hides a real problem.
- Testing in the wrong spot. A test in an upstairs bedroom underestimates basement exposure; test the lowest lived-in level.
- Placing the detector near drafts or humidity. Bathrooms, exterior walls and vents all throw off charcoal kits.
- Letting a charcoal kit sit before mailing. Delays degrade the result.
- Acting on one short-term test. Confirm a high reading before paying for mitigation.
Radon testing sits alongside the other invisible-hazard checks worth doing at home. See signs of mold in your home and how to improve indoor air quality for the broader picture, and if a musty basement is part of what prompted this, what causes a musty basement smell covers a related concern. Everything else is at the air quality hub.