Certified radon tester: what they do and how to hire one

1. What a tester does that a kit does not

EPA's home-buyer guide says a qualified tester evaluates the home and recommends a testing approach. They explain how proper conditions will be kept, and they tell occupants that disturbing the test or the closed-house conditions invalidates the result. They then analyze the data, report the measurement, and provide an independent result.

Testers may use the same passive devices sold as kits, or active continuous monitors that record radon through the test period. EPA says many monitors produce a report that can show unusual swings, and some are built to deter or detect interference. These tests may cost more. EPA says they may give a more reliable result. Ask which device the tester will use, and why.

Sources: EPA: Home Buyer's and Seller's Guide to Radon (2024, PDF).

2. Check the measurement credential before you book

EPA requires states that receive its indoor radon grants to list only providers credentialed through a state process, such as a license, or through one of the two national programs it recognizes: the National Radon Proficiency Program (NRPP) and the National Radon Safety Board (NRSB). Many states license, certify or register radon testers. Most state radon offices can give you a list.

Ask to see the credential. EPA says certification programs usually issue a photo ID that shows the holder's qualifications and its expiration date. If you are in doubt, check with the credentialing organization. NRSB warns that some contractors claim credentials they do not hold. Confirm the credential covers measurement. A mitigation credential covers different work, and a national certification is not a state license.

Sources: EPA: Find a Radon Test Kit or Measurement and Mitigation Professional; EPA: Home Buyer's and Seller's Guide to Radon (2024, PDF); NRSB: Hiring a Radon Professional (2024, PDF).

3. Where the device should go

EPA says the device belongs in the lowest level of the home that could be used regularly, finished or unfinished. That means any space that could serve as a bedroom, play area, family room, den, exercise room or workshop. The tester should choose the spot from how you plan to use the space and tell you where it is.

EPA rules out closets, stairways, hallways, crawl spaces and enclosed areas with high humidity or fast-moving air, such as a kitchen, bathroom, laundry room or furnace room. If you plan to use a basement the current owner does not, say so before the appointment.

Sources: EPA: Home Buyer's and Seller's Guide to Radon (2024, PDF).

4. If the test is for a home sale

EPA notes the potential for test interference in real estate transactions. A tester can use a monitor that records frequent readings, motion or proximity detectors, and records of barometric pressure and temperature. A tester can also use tamper-proof seals on windows, and a non-interference agreement signed by the seller or occupant. Ask which of these the tester uses.

Closed-house conditions mean windows closed, doors closed except for normal entry and exit, and no fans or machines bringing in outside air. A radon system fan should keep running. EPA says disturbing the device or those conditions may invalidate the result, and that doing so is illegal in some states.

A buyer can accept the seller's earlier result or ask for a new test by a qualified tester. Before you accept the earlier result, EPA says to find out the result, who did the test, where in the home it was taken, and what has changed in the structure or the heating and cooling system since that test. If you want a new test, raise it with the seller as soon as possible.

Sources: EPA: Home Buyer's and Seller's Guide to Radon (2024, PDF).

5. What the report should show

EPA's testing checklist records the start and stop times and the test location. Where a state issues ID cards, the tester's ID number should be included or noted in the report. You or the tester should be able to show that testing conditions were not violated during the test.

EPA recommends fixing the home at 4 pCi/L or more and says to consider fixing between 2 and 4 pCi/L. If the result is high, keep the full report. EPA says the mitigation contractor should review the measurement results before starting any work.

Sources: EPA: Home Buyer's and Seller's Guide to Radon (2024, PDF); EPA: Consumer's Guide to Radon Reduction (2025, PDF).

6. Use an independent tester after mitigation

After a system is installed, EPA recommends a test by an independent, qualified tester to confirm the levels came down. When the same person or firm does both the testing and the mitigation, EPA says there is a potential conflict of interest, and that some states may require the homeowner to sign a waiver. If one firm does both, make sure the test follows EPA's Radon Testing Checklist.

Sources: EPA: Home Buyer's and Seller's Guide to Radon (2024, PDF).

Find a credentialed provider

Open the testing page for your city or county and check the tester's credential number against the linked official source before you book. If the result is high, the mitigation listings for the same place are one link away.

Find providers in your area · Check credentials by state

Testing instructions and requirements depend on the test, building and jurisdiction. Use the linked agency guidance and your qualified professional’s instructions for your situation.