How do I test my home for radon?

The short version

Testing for radon is cheap and takes a few minutes of your time. You buy an approved kit, close up the house, set the kit in the right room, leave it for the time on the package, and mail it to the lab. The only way to know your home's level is to test it. Even houses next door to each other can test very differently,^[1] whatever the neighborhood or the map says.

Radon usually collects most in the lowest level of a home.^[1] That is why where you put the kit matters as much as which kit you buy.

What you need

Choose a test kit approved by either NRPP or NRSB,^[1][2] the two national radon certification programs. Approved kits come with instructions, a form for the start and stop times, and a prepaid or paid lab analysis.

When we checked in October 2026, the Virginia Department of Health's radon FAQ (last updated December 17, 2025) said short-term kits run 2 to 6 days and cost $10 to $15 each, and long-term kits run 91 to 365 days and cost $25 to $35 each.^[1] Long-term kits are rarely sold in stores but are available from online vendors.^[1]

Short-term or long-term

Short-term tests stay in the home for two to 90 days, depending on the device, and long-term tests stay for more than 90 days.^[3] A short-term test is the quick screen. A long-term test smooths out the day-to-day and seasonal swings that make one short reading misleading.

Virginia recommends long-term testing whenever possible,^[1] and a device that stays in the home for a year is the most accurate way to learn the home's year-round average.^[1] A sensible plan for most owners is a short-term test now, then a long-term test if the result is close to or above the action level.

When to test

Most homes test highest in winter and lowest in summer, so avoid making your first test a summer one if you can.^[1] Skip short-term tests during unusually severe storms, because heavy rain, high sustained winds and strong low-pressure systems can cause temporary spikes.^[2]

For a short-term test, close windows and outside doors at least 12 hours before the test and keep them closed during it,^[1][3] apart from normal coming and going. Heating and air conditioning fans that recirculate air can run, but fans or machines that bring in outside air should not.^[3]

Where to put the kit

The lowest livable level should always be tested.^[2] An area that is finished, or could easily be finished, counts as livable; crawl spaces, garages and cellars without utilities or headroom, or with exposed dirt or rock, do not.^[2] Pick a room you use regularly, like a bedroom or family room.

Place the device at least 20 inches above the floor and well away from outside walls, fans, windows, humid rooms such as bathrooms and laundry rooms, and openings in the floor such as sumps and plumbing cut-outs.^[2] A shelf or a stack of books on a dresser works well. Put it where children and pets will not move it.

If your house has more than one foundation, test each part. Every section of the home in contact with the ground should be tested, especially foundations of different types at different elevations.^[2] A split-level with a basement under one half and a slab under the other needs two kits.

A minimum 48-hour test period is one of the key conditions for a good short-term measurement.^[1] Leave the kit for the full time on the package, then reseal it and mail it to the lab right away. Results usually come back within a few weeks.^[3]

What the number means

Radon is measured in picocuries per liter of air (pCi/L). The average indoor level is 1.3 pCi/L and outdoor air is about 0.4 pCi/L.^[1][3] EPA recommends fixing a home at 4 pCi/L or higher and considering a fix between 2 and 4 pCi/L.^[6] There is no absolutely safe level.^[1]

One short-term result is not enough to decide on mitigation. Under EPA's approach, as Virginia's health department summarizes it, if the first result is 4.0 to 9.9 pCi/L, take a long-term test and use it to decide on mitigation; if it is 10.0 pCi/L or higher, take a second short-term test and use the average of the two.^[1] If you begin using a lower level of the house, such as a basement, retest on that level.^[3] Our guide on how often to test for radon covers the retest schedule.

Buying or selling a house

Real estate deals usually hire a professional tester, because buyers want a result from someone with no stake in the sale. Depending on the device, a professional radon test usually costs $100 to $200, according to the Virginia Department of Health's testing page (last updated October 22, 2026).^[2] Under Virginia law, anyone conducting or offering radon testing must be listed by the National Radon Proficiency Program or the National Radon Safety Board, or meet another proficiency measure EPA or the Board of Health accepts.^[7]

When time is short, EPA accepts two short-term tests side by side, one test followed straight away by a second identical one in the same spot, or a continuous monitor, each for at least 48 hours.^[4] Any real estate test should include steps to prevent or detect interference, such as motion detectors, tamper-proof seals on windows and a signed non-interference agreement.^[4]

If you have a private well

Radon can also come in through well water and escape into the air when you shower or run the tap. The devices and procedures for testing water are different from those used for air,^[5] so ask a lab or a certified radon professional for a water test kit rather than reusing an air kit.

Stop and call a pro if

• A follow-up test confirms 4 pCi/L or higher. Get quotes from certified mitigators; our guide to what radon mitigation costs in Virginia explains the price.
• You are buying or selling and need a result both sides will trust.
• Your first short-term result is 10 pCi/L or more and you want a fast, professional follow-up.
• You have a private well and the air result is high, or the water result worries you.
• You plan to finish a basement and want radon-resistant features built in.

For more, see whether radon mitigation contractors need to be certified in Virginia, browse other inspection answers, or find radon testing and mitigation businesses.

Ready for a professional test? Describe the job once and licensed businesses near you can quote.