Radon testing is the only way to know whether your home has elevated radon levels. You cannot smell it, see it, or detect it with any sense — and the homes with the highest radon levels often show no correlation with geography, age, or construction style. The EPA estimates that 1 in 15 U.S. homes has elevated radon. Testing takes as little as 48 hours and costs $15–$30 for a DIY kit.
Why You Need to Test
Radon is the second leading cause of lung cancer in the United States after cigarette smoking, responsible for approximately 21,000 deaths annually according to the EPA. The risk is cumulative — it is the product of concentration and time. A home at 4.0 pCi/L poses roughly the same lifetime lung cancer risk as smoking half a pack of cigarettes per day. A home at 20 pCi/L — not uncommon in high-radon zones — roughly equals smoking two packs per day.
The only way to know your home’s radon level is to test it. No map, no neighborhood average, and no visual inspection can substitute for a measurement in your specific home.
Short-Term vs. Long-Term Radon Tests
Short-Term Tests (2–90 Days)
Short-term tests are the most commonly used initial screening method. The standard residential short-term test is a charcoal canister test run for 48–96 hours. Results are available within 3–7 business days after mailing the device to a lab.
- Duration: 48 hours minimum (EPA); 48–96 hours typical for charcoal devices
- Device type: Activated charcoal canister or electret ion chamber
- Conditions required: Closed-house conditions (see below)
- Best for: Initial screening, pre-purchase testing, post-mitigation verification
- Limitation: A single short-term test captures a snapshot — radon levels fluctuate with barometric pressure, temperature, and season. A short-term result may be higher or lower than the home’s true annual average.
Long-Term Tests (90+ Days)
Long-term tests provide a more accurate picture of the home’s actual annual average radon exposure. The standard device is an alpha track detector — a small card with a special plastic film that records radon decay particle tracks over time.
- Duration: 90 days to 1 year (one year is ideal)
- Device type: Alpha track detector
- Conditions required: Normal living conditions (no closed-house protocol)
- Best for: Confirming short-term results, annual monitoring, determining true annual average
- Advantage: Averages out seasonal and pressure fluctuations — provides the most accurate basis for mitigation decisions
EPA guidance: if a short-term test shows between 4.0 and 8.0 pCi/L, conduct a follow-up long-term test or a second short-term test before deciding on mitigation. If the initial short-term test shows 8.0 pCi/L or higher, proceed to mitigation without waiting for a confirmatory test — the risk is sufficient to act immediately.
Where to Place the Radon Test Device
Placement determines whether your result is meaningful. The EPA’s placement protocol:
- Level: Test in the lowest level of the home that is currently used or could be used as living space — even if you do not currently occupy it. If you have an unfinished basement you plan to finish, test there.
- Location within the room: Place the device in the breathing zone — at least 20 inches above the floor and at least 12 inches from any wall
- Away from drafts: Do not place near windows, doors, HVAC vents, or exterior walls where air movement can dilute results
- Away from humidity sources: Do not place near sump pits, laundry areas, or bathrooms — excessive humidity can affect charcoal canister performance
- Accessible but undisturbed: The device should be able to sit undisturbed for the full test duration — not in a high-traffic area where it might be moved
Closed-House Conditions
Short-term tests require closed-house conditions during the test and for 12 hours before the test begins. Closed-house means:
- All windows and exterior doors closed except for brief normal entry/exit
- No whole-house fans or attic fans running
- Normal HVAC operation is permitted (heating and cooling systems can run — they recirculate interior air)
- Ceiling fans are permitted
- Fireplace dampers closed (if not in use)
Closed-house conditions prevent outdoor air from diluting indoor radon to artificially low levels during the test. When conditions are not maintained, short-term results systematically underestimate actual radon levels — exactly the wrong direction for a safety measurement.
Interpreting Your Results
- Below 2.0 pCi/L: Below EPA’s average indoor radon level of 1.3 pCi/L if the home is new. No action required; retest in 2 years.
- 2.0–3.9 pCi/L: Between the national average and the EPA action level. Consider a long-term test to confirm. Some homeowners choose to mitigate at this level regardless, particularly if they have young children or smokers in the home.
- 4.0–7.9 pCi/L: At or above EPA action level. EPA recommends mitigation. Conduct a confirmatory long-term or second short-term test if time allows, then mitigate.
- 8.0 pCi/L or higher: Mitigate without waiting for confirmatory testing. At this level the health risk warrants immediate action.
DIY vs. Professional Testing
DIY test kits (charcoal canisters or alpha track detectors) purchased from hardware stores or online labs are the most cost-effective option for initial and ongoing screening. Cost: $15–$30 including lab analysis. Most state radon programs recommend purchasing from a lab certified by the National Radon Proficiency Program (NRPP) or National Radon Safety Board (NRSB).
Professional testing uses the same device types but is conducted and placed by a certified radon measurement professional. Professional testing is required or preferred in specific situations:
- Real estate transactions where the buyer requires a certified measurement
- Post-mitigation verification where the mitigator or a warranty requires professional confirmation
- Rental properties in states where landlord testing requirements specify professional measurement
- Situations involving litigation or insurance where certified chain-of-custody testing is required
How Often to Test
- Initial test: If you have never tested, test now — regardless of when you moved in or how long you have lived there
- After mitigation: Test within 24 hours of system installation (if using a continuous monitor) or place a short-term test 24+ hours post-installation; run for 48 hours minimum
- Routine retesting: EPA recommends retesting every 2 years even in mitigated homes — to confirm continued performance and catch new entry pathways from foundation settling or renovation
- After renovations: Any work that involves the foundation, basement, or significant changes to the HVAC system warrants a new test
- When buying a home: Always test — or require a recent test result — before closing
Frequently Asked Questions
How accurate are DIY radon test kits?
DIY charcoal canister kits analyzed by NRPP- or NRSB-certified labs are accurate to within ±10–15% under controlled conditions. This is sufficient precision for screening decisions. The larger source of variation is not the device itself but testing conditions — an improperly placed device or violated closed-house conditions introduce more error than the device’s inherent measurement uncertainty.
What time of year is best to test for radon?
Winter typically produces higher radon readings than summer — windows are kept closed, stack effect is stronger, and atmospheric pressure patterns tend to draw more soil gas into the home. Testing in winter gives a closer approximation of worst-case conditions. However, because any result at or above 4.0 pCi/L warrants mitigation regardless of season, the best time to test is simply now — not after waiting for an optimal season.
Can I test for radon myself or do I need a professional?
DIY testing is appropriate and recommended for the vast majority of homeowners. Purchase a certified short-term or long-term kit, follow the placement and closed-house instructions, and mail to the lab. Professional testing is required only for real estate transactions in some states, post-litigation measurements, or situations where certified chain-of-custody documentation is needed.
My neighbor’s home tested low — does that mean mine will too?
No. Radon levels vary dramatically between adjacent homes — sometimes between rooms in the same home. Differences in sub-slab aggregate, foundation type, construction methods, HVAC configuration, and soil permeability can produce completely different radon levels in homes built side by side. Your home must be tested independently.
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