Before you buy or hire
Choose the test for the decision, not the packaging
Radon cannot be screened by smell, home age, foundation style, or a county color on a map. EPA says the zone map describes regional potential and should not determine whether an individual home needs testing. Adjacent homes can produce different results. Start by naming the decision: an initial household screen, a transaction with a deadline, a better estimate of year-round average, or verification after mitigation. That decision determines the useful measurement window and protocol.
A low price is useful only if the device comes from a qualified laboratory or service pathway, can finish within the needed window, and includes clear activation, placement, return, and result instructions. A reusable display is useful only if its exact device status and quality documentation fit the purpose. This guide therefore compares test categories and evidence, not unsupported brands. The companion digital-versus-charcoal guide goes deeper on handling and feedback, while the mitigation follow-up guide covers post-installation verification.[1][4][5]
Separate short-term speed from long-term representation
EPA's March 2024 real-estate guide defines short-term tests as remaining in the home from two to 90 days, depending on the device, and says every radon test should run at least 48 hours. Charcoal canisters, charcoal liquid scintillation devices, electret ion chambers, alpha-track devices, and continuous monitors may serve different short-term roles. Follow the exact stated minimum and maximum. A result from an underexposed device or a kit returned after its allowed window is not rescued by averaging.
Long-term tests remain for more than 90 days. Because radon changes from day to day and season to season, EPA says a long-term result is more likely to represent the year-round average than a short test. That makes long-term alpha-track or another qualified long-term method useful when time permits and the owner wants a broader exposure picture. It does not make a long test the answer to every deadline, and a quick short test should not be described as a guaranteed annual average.[1][5]
Verify the device, laboratory, and quality path
For a mail-in kit, confirm the named laboratory, device type, expiration or use window, included analysis, shipping requirements, and how the report identifies location, exposure dates, units, and result. EPA tells consumers to use a device from a qualified laboratory and to ask their state radon office about appropriate devices and requirements. A marketplace listing that says accurate without identifying its laboratory and current qualification leaves a material gap in the purchase evidence.
For a continuous monitor or paid service, ask which current measurement and instrument standards apply, how calibration and quality assurance are maintained, and how unusual readings or invalid conditions are documented. EPA's standards page points to residential measurement, instrument performance, and measurement-system quality requirements; it does not certify every consumer device displayed online. State rules can be more specific. A professional credential or proficiency listing should be current and verified with the state program or issuing organization.[2][3][1]
Create and record closed-building conditions
For a short-term test, keep windows and exterior doors closed except for normal entry and exit. When a short test lasts less than four days, EPA directs occupants to establish closed-building conditions at least 12 hours before the test and not to conduct it during severe storms or periods of high winds. Operate heating or cooling normally, but do not use fans or other machines that bring outside air into the test area unless the applicable instructions allow them.
Write down when closed-building conditions began, test start and stop, device ID, room, floor, weather observations requested by the instructions, and any interruption. Do not move the detector, open windows to influence a result, or place it where a child, pet, cleaner, or fan will disturb it. In a real-estate test, the qualified tester may add tamper indicators or environmental records. Those controls make the result more defensible; they are not features to imitate selectively while ignoring the full protocol.[1][3]
Place the detector in representative occupied air
EPA recommends testing the lowest level that could be used regularly, whether finished or unfinished. That may be a current bedroom, family room, exercise room, den, play area, or workshop, or a lower level a buyer expects to use. It is not automatically the darkest basement corner. Do not test in a closet, stairway, hallway, crawlspace, or enclosed area with high humidity or high air velocity such as a bathroom, kitchen, laundry, or furnace room.
For the short-test procedure in EPA's real-estate guide, place the device at least 20 inches above the floor, where it is undisturbed and away from drafts, high heat, high humidity, and exterior walls. The device instructions and applicable state or professional protocol may add separation or multiple-location rules, so use them rather than inventing a universal tabletop diagram. Record the actual location with a photo or sketch so a follow-up test can be meaningfully compared.[1][3]
Plan real-estate timing before the contingency expires
A home purchase compresses testing into negotiation and inspection deadlines. Agree in writing on the location, qualified person, device or test option, start and stop dates, result sharing, costs, and how mitigation will be handled if needed. EPA's real-estate guide describes simultaneous short-term devices, sequential short-term devices, or a continuous monitor used for at least 48 hours as transaction options, with interference controls. State requirements or contract terms may be stricter.
Do not buy a slow mail-in kit on the last inspection day and assume laboratory transit will fit. Ask when the laboratory receives samples, whether return shipping is prepaid and tracked, what invalidates exposure, and when a signed report is expected. Contact the state radon office first, then a currently qualified measurement professional when the transaction, dispute, vacant property, unusual foundation, or interference risk makes a self-test poor evidence. Keep prior results and changes to the building with the new report.[1][2][3]
Decide the follow-up before opening the package
A completed result needs a written next step. For non-transaction testing, use EPA and state guidance to decide whether a short result calls for another short test or a long-term confirmation, considering the result and how quickly a decision is needed. In the March 2024 transaction options, EPA describes averaging two simultaneous or sequential short-term tests, or using a continuous-monitor average, and recommends fixing when the relevant result is 4 pCi/L or higher. Do not average unrelated rooms or seasons merely to cross a threshold.
EPA recommends fixing a home at 4 pCi/L or more and notes that levels below 4 still carry risk and may sometimes be reduced. A single hourly spike on a consumer display is not interpreted like a completed protocol, while an invalid kit is not a reassuring low result. Preserve the report, check whether conditions were followed, and obtain state-program or qualified-provider guidance for conflicting, borderline, unusually high, or disputed results rather than repeatedly testing until a preferred number appears.[1][5][4]
Escalate from measurement to qualified mitigation
When the applicable result indicates the home should be fixed, move from shopping for detectors to selecting a qualified mitigation professional. Start with the state radon program because licensing, registration, measurement, disclosure, and mitigation requirements differ. Where the state does not run its own list, EPA identifies national proficiency programs that list qualified providers. Verify the credential and expiration; EPA's reference to these programs is not a product or contractor endorsement.
Ask for a written system proposal, applicable standard, warning device, electrical and exhaust scope, post-installation test, documentation, warranty, maintenance, and retest plan. Do not treat sealing visible cracks alone, moving a monitor upstairs, or opening windows as mitigation. After installation, use the dedicated post-mitigation guide to verify reduction and keep testing over time. A purchase is successful when it produces a valid decision and response, not when its display supplies the lowest number.[2][1][3][5]
| Decision | Useful path | Evidence to verify | Main limitation |
|---|---|---|---|
| Quick household screen | Qualified short-term device | Exposure window and lab process | Less representative of annual average |
| Year-round estimate | Qualified test over more than 90 days | Device qualification and full exposure | Does not fit a short deadline |
| Real-estate decision | State-compliant qualified protocol | Provider, interference controls, report timing | Contract and state requirements vary |
| After mitigation | Documented follow-up test | System status, location, conditions | Equipment indicators do not measure radon |
Related reading and tools
Sources and manuals
- Home Buyer's and Seller's Guide to Radon, March 2024U.S. Environmental Protection Agency
- How can you find a qualified radon service provider in your area?U.S. Environmental Protection Agency
- Radon Standards of PracticeU.S. Environmental Protection Agency
- EPA Map of Radon Zones and Supplemental InformationU.S. Environmental Protection Agency
- A Citizen's Guide to RadonU.S. EPA
FAQ
Is a short-term radon kit accurate enough to act on?
A qualified short-term device can support a decision when its minimum exposure, closed-building, placement, handling, and follow-up instructions are followed. It is less likely than a long-term test to represent the year-round average.
Is a long-term radon test always better?
It better represents day-to-day and seasonal variation, but it takes more than 90 days and may not fit a real-estate or other urgent decision. Choose the protocol for the decision and applicable rules.
Where should I put a radon detector?
Use the lowest level that could be used regularly, in representative occupied air, and follow the device and state protocol. Avoid high-humidity, high-airflow, drafty, hot, or easily disturbed locations.
What happens if the result is 4 pCi/L or higher?
EPA recommends fixing the home. Confirm that the applicable test process was valid, then contact the state radon program and a qualified mitigation professional for the response and post-installation verification.
Does a low-radon-zone map mean I can skip testing?
No. EPA says its zone map should not determine whether an individual home needs testing. Only a properly conducted test describes that home.
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