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How to Test Your Home for Radon

Testing is the only way to know your radon level. You can't see it, smell it, or feel it. And your neighbor's test results don't mean anything for your house — levels can vary wildly between homes on the same street. Here's what you need to know.

Types of Radon Tests

Short-Term Tests (2-7 Days)

These are the quick-and-dirty option. Charcoal canisters or electret ion chambers sit in your home for 48 hours to 7 days, then go to a lab for analysis. You'll get results in about a week after the test period ends.

Best for: Initial screening, real estate transactions, and getting a fast answer.

Downsides: They're a snapshot. Radon levels fluctuate with weather, season, and how you're running your HVAC. A short-term test can over- or under-read your true annual average.

Cost: $15-$30 for a DIY kit from a hardware store. $100-$250 for a professional to set it up.

Continuous Radon Monitors (CRM) — 48+ Hours

Electronic devices that measure radon continuously and log readings every hour. A professional drops one off, picks it up 48 hours later, and prints results on the spot. These are tamper-resistant, which is why they're preferred for real estate transactions.

Best for: Real estate transactions (most reliable short-term method), situations where you want hourly data.

Cost: $150-$300 for a professional test with a CRM.

Long-Term Tests (90+ Days)

Alpha track detectors or electret ion chambers that sit in your home for 3-12 months. They give you a true annual average, which is what actually matters for health risk.

Best for: Confirming a short-term result, getting an accurate annual average, post-mitigation verification.

Cost: $20-$40 for the test kit.

How to Do a Short-Term Test Properly

Messing up the test conditions is the #1 reason for inaccurate results. Follow these rules:

  1. Closed-house conditions: Keep all windows and doors closed for at least 12 hours BEFORE starting the test, and keep them closed for the entire test period. Normal entry and exit is fine — just don't leave doors hanging open.
  2. No fans pulling air from outside: Turn off whole-house fans, attic fans, and window fans. Your regular HVAC system is fine to run normally.
  3. Place the test in the lowest livable level: If you have a basement that anyone uses — even just as a TV room — test there. If nobody uses the basement, test the first floor. Don't test in a crawlspace.
  4. Keep it 3+ feet from exterior walls and windows: And at least 20 inches off the floor. A bookshelf or end table works great.
  5. Don't test during storms or high winds: Weather extremes can skew results. A calm week is ideal.
  6. Don't disturb the test device: Once placed, leave it alone. Don't move it, stack things on it, or let the cat knock it off the shelf.

Understanding Your Results

Results are measured in picocuries per liter (pCi/L). Here's what the numbers mean:

  • Below 2.0 pCi/L: Low risk. You're good. Re-test in a few years.
  • 2.0 - 3.9 pCi/L: The EPA says "consider fixing." It's not urgent, but it's worth addressing. Lots of homeowners mitigate at this level.
  • 4.0+ pCi/L: Above the EPA action level. Get it fixed. The higher the number, the sooner you should act.

For a detailed breakdown with specific actions for your level, use our result interpreter tool.

When to Re-Test

  • Every 2 years: EPA recommendation for all homes, even if the first test was low.
  • After renovations: Especially anything that changes your foundation (finishing a basement, adding a room over a crawlspace, new HVAC).
  • After buying a home: Even if the seller's test was low. Conditions change.
  • After mitigation: Test 24 hours after the system is running, then again at 6 months, then every 2 years.
  • Different season: If your first test was in summer, consider re-testing in winter. Radon levels are typically higher in cold months when houses are sealed up.

DIY vs. Professional Testing

For an initial screen of your own home, a $15 DIY kit from the hardware store is perfectly fine. Follow the instructions, mail it to the lab, and you'll have a number.

Hire a professional when:

  • You're in a real estate transaction (many states require certified testers)
  • You want tamper-proof documentation
  • Your DIY test came back borderline (3.0-5.0) and you want a more precise reading
  • You need results fast (CRM gives hourly data in 48 hours)
Find a Testing ProfessionalInterpret Your Results

Sources: EPA "A Citizen's Guide to Radon," AARST Consortium on National Radon Standards.