How long does a radon test take?

Short-term charcoal kits run 2 to 7 days and then go to a lab, with results in about a week. Long-term alpha-track kits stay in place 90 days to a year. A continuous digital monitor shows a first reading within hours and a reliable average after about a week.

Where should I put the radon test?

In the lowest level you use regularly (a finished basement or the first floor), 2 to 6 feet above the floor, at least 3 feet from windows and exterior doors, away from drafts, heat sources and high humidity, and not in a kitchen or bathroom. Keep it out of crawlspaces and closets.

What is a bad radon reading?

The EPA action level is 4 pCi/L: fix at or above it. Between 2 and 4 the EPA says to consider fixing. The World Health Organization suggests a lower reference level of 2.7 pCi/L (100 Bq/m3). No level is considered fully safe.

Can I test for radon myself?

Yes. Do-it-yourself kits and consumer monitors are accurate enough for deciding whether to mitigate. For a real-estate transaction, most states and lenders expect a certified professional to run the test so neither party can tamper with it.

How to test for radon

Radon is the only major indoor air hazard you can settle with a test that costs about as much as a pizza. This guide covers the three ways to test, exactly where to put the device, how to avoid the mistakes that invalidate results, and what to do with the number you get back. If you haven't already, check your ZIP's predicted level to see how urgent this is for your area.

Why every home should be tested

Radon is a radioactive gas produced as uranium in soil and rock decays. It moves through the ground and enters a house through cracks in the slab, sump pits, floor drains, gaps around pipes and the pores of block walls. Because the house is slightly depressurized compared to the soil (heating, exhaust fans and wind all pull air upward), the building acts like a weak vacuum on the ground beneath it. The EPA attributes about 21,000 US lung-cancer deaths a year to radon and recommends testing every home below the third floor, regardless of the county's EPA zone or a neighbor's result. Two houses on the same street routinely differ by several times, because the soil pocket, foundation construction and ventilation under each one are different. Area predictions such as the ones on this site tell you how urgent a test is - not whether you can skip it.

The three ways to test

1. Short-term kit (2-7 days)

An activated-charcoal canister or liquid-scintillation vial that absorbs radon for a few days and is then mailed to a lab. Cheapest option, widely sold, and often free or discounted through state radon programs. Best for a first look. Its weakness is that radon swings day to day with weather and season, so a single 3-day snapshot can miss the long-term average.Short-term kits on Amazon.

2. Long-term kit (90 days to 1 year)

An alpha-track or electret detector that integrates exposure over months. This is the number that best matches the health risk, because it averages across seasons. Use one to confirm a short-term result between 2 and 8 pCi/L before spending on mitigation.Long-term kits on Amazon.

3. Continuous digital monitor

A battery or plug-in device that measures radon continuously and displays 1-day, 7-day and long-term averages. Higher upfront cost, but it replaces repeated kits, shows how your level changes with weather and HVAC use, and verifies a mitigation system is still working years later. Worth it if your area is predicted near or above 4 pCi/L, or if you have a finished basement someone sleeps in.Continuous monitors.

Where to place the test

Lowest lived-in level. A finished basement if you use it regularly; otherwise the first floor. The EPA action level applies to living space, but testing the basement is the conservative choice if you may finish it later.
Height and distance. 2-6 feet above the floor; at least 3 feet from exterior doors and windows; at least 1 foot from exterior walls; not in direct sunlight or drafts from vents.
Avoid kitchens, bathrooms, laundry rooms and crawlspaces. Humidity and air movement skew charcoal kits.
Leave it undisturbed for the entire period; note the start and end times exactly.

Closed-house conditions

For any test shorter than 90 days, keep windows and exterior doors closed (normal entry and exit is fine) for 12 hours before and throughout the test. Do not run whole-house fans or window air conditioners that pull in outdoor air; central HVAC that recirculates indoor air is fine. Avoid testing during severe storms or very high winds, which push results in both directions. Heating season generally gives the highest readings, so a winter test is the conservative one.

Reading your result

Result (pCi/L)	What the EPA says	Sensible next step
Below 2	Below the "consider fixing" threshold	Re-test every few years, after renovations, or if you finish the basement.
2 to 4	Consider fixing	Run a long-term test or a monitor for a season; mitigate if it stays above 2 and you use the lower level.
4 to 8	Fix your home	Confirm with a second short-term or long-term test, then get mitigation bids.
Above 8	Fix your home	Confirm with a second short-term test right away and mitigate; don't wait for a 90-day result.

The EPA's two-test rule: if a first short-term test is 4 pCi/L or higher, run a second test (short-term for a quick answer, long-term for the best estimate) and act on the average of the two - or on the second test alone if it was long-term.

When to hire a professional

For a home sale, a school or a daycare, or if you simply want a defensible number, hire a measurement professional certified by NRPP or NRSB and listed by your state. They use calibrated continuous monitors with tamper detection and produce an hourly log. Find one through the EPA's find-a-professional page. If the result is high, the next step is our mitigation guide; if you're buying or selling, read radon and real estate.

Radon testing FAQ

How long does a radon test take?: Short-term charcoal kits run 2 to 7 days and then go to a lab, with results in about a week. Long-term alpha-track kits stay in place 90 days to a year. A continuous digital monitor shows a first reading within hours and a reliable average after about a week.
Where should I put the radon test?: In the lowest level you use regularly (a finished basement or the first floor), 2 to 6 feet above the floor, at least 3 feet from windows and exterior doors, away from drafts, heat sources and high humidity, and not in a kitchen or bathroom. Keep it out of crawlspaces and closets.
What is a bad radon reading?: The EPA action level is 4 pCi/L: fix at or above it. Between 2 and 4 the EPA says to consider fixing. The World Health Organization suggests a lower reference level of 2.7 pCi/L (100 Bq/m3). No level is considered fully safe.
Can I test for radon myself?: Yes. Do-it-yourself kits and consumer monitors are accurate enough for deciding whether to mitigate. For a real-estate transaction, most states and lenders expect a certified professional to run the test so neither party can tamper with it.

Affiliate links above are marked; we may earn a commission at no extra cost to you. Guidance follows EPA's Citizen's Guide to Radon and Home Buyer's and Seller's Guide.