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Certified radon testing professionals

What a certified radon tester does, when to hire one instead of using a kit, what happens during the test, what the report should show, and testers listed by state.

Updated October 2, 2026

Short answer

What a certified radon tester does

A tester places devices under the conditions a reliable result needs, guards the test against interference and reports the result. Very often it is a home inspector.

A qualified tester knows the proper conditions, devices and guidelines for a reliable result, and can:

  • Evaluate the home and recommend a testing approach
  • Explain how proper conditions are kept during the test
  • Make sure the occupants know a reliable result depends on them
  • Analyze the data and report the result
  • Give you an independent test result

Passive devices need no power: they sit in the home for a set time and go to a laboratory for analysis, and they are generally inexpensive. Active devices, continuous radon monitors and continuous working level monitors, record the level as they run, and many produce a report that can reveal unusual swings during the test. They may cost more, but may give a more reliable result.

TestHow long it runsWhat it is for
Short-term testStays in the home from 2 to 90 days, depending on the device, and for a minimum of 48 hours.A faster screening result. Because radon levels vary from day to day and season to season, it is less likely than a long-term test to tell you the year-round average.
Long-term testStays in the home for more than 90 days.It is more likely than a short-term test to tell you the home's year-round average radon level.
Continuous monitorLogs readings for the whole test, run as a short-term or a long-term test under the same durations in EPA guidance.Logs a graph over time, so you can see trends and spot anomalies rather than a single number.
The three kinds of radon test and how long each runs.

Choosing

A kit or a professional?

You can test your home yourself or hire a qualified radon test company. Two cases point to a qualified tester.

In a home sale

Buyers and sellers often have the test done by a qualified radon tester, because there is a potential for test interference in a real estate transaction. Any real estate test should include steps to prevent or detect it.

After mitigation

EPA recommends an independent, qualified tester for the test after a system is installed, because a potential conflict of interest exists when the same firm tests and installs. Some states also require testers to follow a specific testing protocol.

If you are testing in a real estate transaction and you need results quickly, any of the following three options for short-term tests are acceptable in determining whether the home should be fixed.

  1. Option 1. Two tests at the same time

    Passive

    Take two short-term tests at the same time in the same location for at least 48 hours.

    What to do nextFix the home if the average of the two tests is 4 pCi/L or more.

    Two tests taken at the same time (simultaneous) would improve the precision of this radon test.

  2. Option 2. One test, then a second

    Passive

    Take an initial short-term test for at least 48 hours. Immediately upon completing the first test, do a second test using an identical device in the same location as the first test.

    What to do nextFix the home if the average of the two tests is 4 pCi/L or more.

    One test followed by another test (sequential) would most likely give a better representation of the seasonal average.

  3. Option 3. A continuous monitor

    Active

    Test the home with a continuous monitor for at least 48 hours.

    What to do nextFix the home if the average radon level is 4 pCi/L or more.

    Both active and passive devices may have features which help to prevent test interference.

Any real estate test for radon should include steps to prevent or detect interference with the test device. Your state radon office can help you decide which option is best.

The three short-term options for a home sale, and what to do with each result.

The directory

Radon testers by state

1,088 businesses are listed for radon measurement. Choose a state for its own licensing rule and its list.

Only states with listings of their own are in the table. Every state has its own page, with its licensing rule: choose it on the map or in the search above.

1,088 professionals listed. Showing 1 to 1224.

On this page: 4 testing and mitigation, 820 testing

Testing and mitigation (4)

Testing (820)

Show 12 more on this page

Credentials

Certification and state licenses for testers

Your state's rule first; a national certification where the state has none.

NRPP Certified Measurement Professional
NRPP's search lists its Certified Measurement Professionals, and NRPP requires every certified individual to work to the applicable ANSI/AARST standards.
NRSB Technician and Specialist
An NRSB Radon Measurement Technician is qualified to place and retrieve devices, under the supervision of an NRSB-certified Radon Measurement Specialist. NRSB's measurement professionals must use NRSB-approved devices.
The protocol for homes
ANSI/AARST MAH-2023 sets procedures and minimum requirements for measuring radon in single-family homes. Its Sections 8 and 9 add requirements for professional testing: qualification, onsite documentation and reporting.

  • 14

    Say they license or certify radon professionals

    The state's own radon program page says the state licenses, certifies or registers people who test or mitigate.

    California, Colorado, Florida, Illinois, Indiana, Iowa, Maine, Minnesota, Nebraska, New Jersey, Ohio, Pennsylvania, Rhode Island, West Virginia

  • 9

    Say they do not

    The state's own page says it does not license or certify radon professionals. National certification is then the credential to ask for.

    Connecticut, Georgia, Michigan, Montana, New Hampshire, New Mexico, New York, Texas, Wisconsin

  • 2

    Say something else

    The page speaks to credentials without a yes or no: a rule that names the national programs, or a program still being written.

    North Carolina, Virginia

The other 26 program pages (of 50 states and the District of Columbia) do not state a rule, or have not been read yet. Read from each state's own radon program page, checked on September 25, 2026. Each state's page here quotes its program's own sentence; choose yours on the map above or on the state radon programs page.

Step by step

What happens during a professional test

The testing checklist, in the order it happens.

  1. Before

    The occupants are told why testing conditions matter and given written instructions. For a test of two to four days, windows and outside doors stay closed for at least 12 hours before it starts.

  2. Placement

    The device goes in the lowest level of the home that could be used regularly, finished or not, at a spot the tester picks for how the buyer means to use the space. Not in a closet, stairway, hallway or crawl space.

  3. During

    Windows stay closed and doors closed except for normal entry and exit. Heating and cooling run normally, nobody moves the device, and a working radon system stays on.

  4. Guarding the test

    A tester may use a device that records the level often, a motion or proximity detector, barometric pressure and temperature records, tamper-proof seals on windows, or a signed non-interference agreement.

  5. How long

    At least 48 hours. Some devices need longer, such as a 7-day charcoal canister. A long-term test runs more than 90 days.

  6. After

    The tester analyzes the data and reports the result. If you need it quickly, ask how long results take and whether expedited service is available.

Disturbing the device or the closed-house conditions may invalidate the result, and is illegal in some states. If the seller or tester cannot confirm every checklist item was met, take another test.

The paperwork

The report, and what to ask

What the test report should show

  • The tester's ID number, where there is one
  • Start and stop times and the test location
  • The result, analyzed and reported by the tester
  • For a continuous monitor, the readings over time, which can reveal unusual swings
  • How the tester can show the testing conditions were not violated

Questions to ask a tester

  • Are you licensed where my state requires it, or certified by NRPP or NRSB? Can I see the ID card?
  • Which device will you use, and does it record readings over time?
  • How will you prevent or detect interference with the test?
  • Where will you place the device, and why there?
  • How long will the test run, and when will I have the report?
  • Will anyone in your firm also offer to fix the home?

On cost: passive devices are generally inexpensive, and active devices may cost more. Published prices are on what a radon test costs, and free or discounted kits by state on free radon test kits.

Before you book

Check a tester's credential

Your state radon office can also give you its approved list of radon testing companies, and tell you its certification requirements.

  1. Your state's own list

    Start with your state's radon program. Licensing is done by the state, and most states can give you a list of radon service providers working there.

  2. NRPP's search

    The National Radon Proficiency Program's search finds its Certified Mitigation Specialists and Certified Measurement Professionals by area, by name, or by the 6-digit NRPP ID number a professional can give you.

  3. NRSB's search

    The National Radon Safety Board's search finds a professional in your area, or confirms that a named professional is NRSB certified.

  4. The ID card

    The programs usually issue a photo ID card showing the holder's qualifications and its expiry date. Ask to see it, and if in doubt, check with the body that issued it.

Trust

How these listings are verified

No tester pays to be listed, labelled or placed higher.

  • Listed by state registry

    This business appears on a state's published list of licensed radon professionals, which Radon411 read directly from the state's own site. The business has not confirmed these details itself.

  • Claimed profile

    The business confirmed these details itself. Radon411 has not independently checked them against an official record.

  • Business information verified

    Radon411 checked this business's details against an official record, such as a state contractor registry. This is a business status. It does not mean any specific certification has been verified, see each certification below for that.

  • Certification verified

    Radon411 retrieved this credential directly from the issuing body's own record and confirmed it matches this business.

  • Not yet verified

    The business, or a list it was imported from, reports this credential. Radon411 has not checked it against the issuing body's own record, so treat it as self-reported until it is.

  • Unverified

    This business's information was imported from a public source and has not yet been checked by Radon411 or confirmed by the business itself.

Three rules that never change

No one pays for a label. A label comes from where a listing was read or what was checked against the issuing body's own record. Approving a business's claim on its own listing can never mark a credential as verified.

No one pays for a place in the order. Lists are ordered by how much has been checked, then by name. A paid listing tier is not an input to the order at all.

No leads are sold. There is no quote form here. You contact a business directly, by its own website or phone number, and Radon411 never passes your details to anyone.

Run a radon business? Claim your listing to correct its details, or ask to be added.

Questions

Common questions

What does a certified radon tester do?

Evaluates the home, recommends a testing approach, keeps the test conditions right, analyzes the data, reports the result and gives you an independent result.

Do home inspectors test for radon?

Many do: a qualified radon tester is very often a home inspector. Check that the inspector holds the credential your state requires, or a national one.

How long does a professional radon test take?

At least 48 hours, and longer for some devices, such as a 7-day charcoal canister. Closed-house conditions start 12 hours before a test of two to four days.

Do I need a licensed tester in my state?

It depends on the state. Its page here quotes its own program's rule with the date it was read; see the states grouped by what they say.

What do I have to do during the test?

Keep windows closed and doors closed except for normal entry and exit, run heating and cooling normally, and leave the device alone. Small exhaust fans used briefly may run.

Should the company that tests also fix the home?

It can, but that is a potential conflict of interest, and EPA recommends an independent, qualified tester for the test after mitigation.

Next steps

Where to go next