How to Test for Radon in Your Home

Why Testing for Radon Matters

Radon is a colorless, odorless radioactive gas that forms naturally from uranium decay in soil and rock. It seeps into homes through foundation cracks, sump pits, and gaps around pipes — accumulating to dangerous levels in enclosed spaces. It's the second leading cause of lung cancer in the United States, responsible for approximately 21,000 deaths per year according to the EPA.

The only way to know how to test for radon effectively — and whether your home is safe — is to actually measure it. You can't smell it, taste it, or detect it without a test.

Step 1: Choose the Right Radon Test

Short-Term Charcoal Test (48–96 Hours)

Short-term charcoal canisters are the most common DIY approach. Activated charcoal passively absorbs radon gas during the testing window. You mail the sealed canister to a certified lab, which measures the gamma radiation from radon decay products.

• Cost: $15–$30 (kit + lab fee, often bundled)
• Turnaround: Results in 1–2 weeks
• Best for: Initial screening, real estate transactions, post-mitigation confirmation
• Limitation: It's a snapshot — radon fluctuates with weather, seasons, and HVAC settings

Long-Term Alpha Track Test (90–365 Days)

Alpha track detectors record alpha particle hits from radon decay over months, giving you a true annual average rather than a weather-dependent snapshot.

• Cost: $25–$45
• Best for: Understanding real chronic exposure levels, confirming long-term mitigation performance
• Advantage: Seasonal variation is averaged out — you get the number that actually matters for health risk

Electret Ion Chamber Test

Electret ion chambers (EICs) are high-sensitivity passive detectors used mostly by professionals. A charged disk measures electrical changes from ionizing radiation. They can be used for both short- and long-term periods and produce precise results.

• Cost: $100–$250 (usually professional deployment)
• Use case: When accuracy requirements are highest — commercial buildings, multi-family units, or homes with very high radon and complex HVAC systems

Step 2: Place the Test Correctly

Placement is the most common mistake in DIY radon testing. Get it wrong and your result means nothing.

Where to place it:

• Lowest livable level — basement first, ground floor if no basement
• At least 20 inches above the floor (radon pools near the floor, so this gives a more representative reading)
• Interior room that's used regularly — not a storage closet or bathroom
• Away from exterior walls, windows, doors, sump pits, and HVAC vents

Closed-house conditions (short-term tests only):

Close all windows and exterior doors at least 12 hours before starting and keep them closed throughout the test. Your HVAC can run normally — it does not affect results. Don't test during severe weather or when windows are normally left open.

Long-term tests don't require closed-house conditions — they run through all seasons, which is the whole point.

Step 3: When to Go Professional

Professional Short-Term Testing

A certified radon tester places a continuous electronic radon monitor (CRM) in your home for 48–72 hours. Unlike passive kits, a CRM records radon levels hourly and flags any anomalies — making it much harder for results to be manipulated.

• Cost: $150–$300
• Certification: Look for NRPP (National Radon Proficiency Program) or NRSB (National Radon Safety Board) certification
• Why it's worth it: For real estate deals, a certified professional result is more defensible; some states require it for seller disclosures

Professional Long-Term Testing

A certified tester deploys multiple passive or active detectors in different areas of the home over 90+ days. Useful for homes with complicated layouts — multiple foundation types, finished basements, and crawl spaces under separate sections.

• Cost: $200–$400
• Advantage: Year-round data captures true seasonal variation; results include a certified report

Understanding Your Results

Radon is measured in pCi/L (picocuries per liter of air). Here's what the numbers mean:

The EPA action level of 4 pCi/L has been the standard since 1988. Some health organizations suggest that action is warranted even lower — at 2–4 pCi/L — because there is no completely safe level of radon exposure.

Important: The national average indoor radon level is 1.3 pCi/L. If your test comes back at 4.0 pCi/L or higher, you're at more than three times the national average.

What to Do If Your Radon Is High

If your result is at or above 4 pCi/L, the next step is radon mitigation — not another test. Sub-slab depressurization is the most common and effective method, typically reducing levels by 50–99%. A certified mitigator will assess your foundation, install a pipe and fan system, and retest after installation to confirm results.

For levels between 2 and 4 pCi/L, run a long-term alpha track test to get your true annual average before deciding. If the long-term test confirms elevated levels, mitigation is worthwhile.

Find a certified radon mitigator in your state →

How to Test for Radon: Quick Summary

1. Buy a short-term charcoal test kit ($15–$30) or hire a certified professional ($150–$300)
2. Place it correctly — lowest livable level, away from windows and vents
3. Maintain closed-house conditions for 48–96 hours (short-term kits)
4. Mail it to the lab and wait 1–2 weeks for results
5. If results are 4 pCi/L or higher — contact a certified mitigator immediately
6. If results are 2–4 pCi/L — run a long-term test to confirm your annual average

Testing for radon takes less than 10 minutes of actual effort. For a $20 test kit, there's no reason to leave a health risk of this magnitude unknown.

Browse certified mitigators by state →