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Testing and mitigating your home for radon

A row of house roofs with mountains and sky behind them.

Radon is the second leading cause of lung cancer and is found at elevated levels in one out of every two Colorado homes. 

Thankfully, it is easy to identify and fix a radon problem.

Testing your home for radon

Test for radon with an approved “do it yourself” radon test device or hire a licensed radon measurement professional.

We don’t compete with private industry and can't test your home, we provide information and advice only.

There are many kinds of low-cost "do it yourself" radon test kits available at home improvement stores from about $10 to $50.


Short-term tests take 48-120 hours to complete:

  • The house is closed for 12 hours, then the testing device is activated or opened and left in place for 48 hours or more. 
  • Charcoal canisters are generally used, although electronic instruments may also be used.

Long-term tests take 91 days to one year to complete and are conducted with the house under normal living conditions:

  • Alpha-track detectors or electronic detection instruments are used.
  • Long-term test results give a more representative picture of the true radon levels in the home over time, as fluctuations due to changes in ambient temperature and barometric pressure are detected and factored into the final average.

The best place for testing radon levels depends whether you’re testing your home for a real estate transaction or for your own purposes:

  • If you’re testing to determine whether your home has radon levels warranting mitigation, the EPA recommends testing in the lowest living area of your home.
  • For a real estate transaction, the EPA recommends testing in the lowest area that could be modified to become a living area, such as an unfinished basement.

Radon testing is important for a healthy home. All homes should be tested for radon – single family homes, manufactured homes, and apartments. If you find a radon problem, all homes can be fixed with a mitigation system!

It is always a good time to test for radon as long as you can achieve closed building conditions. Some people find this easier to do in the winter.

Getting started

Close all exterior windows and doors 12 hours before starting the test and keep them closed throughout your test. You can come and go as you normally would, but don’t leave the door open for a long time. Most heating and AC units can operate as normal. The test should run for a minimum of 2 days (48 hours).

Be sure to read these instructions and the instructions that are packaged with the test kit!

Test kit placement

Place the test in the lowest inhabitable level of your home, such as the ground floor or basement (even if it’s unfinished).

The test should be placed on a surface 2-7 feet above the floor, such as a table or countertop, out of the reach of children or pets. You may want to close the door to the room if the test could be disturbed by children or pets.

Place the test in an open and centralized area where someone could spend a lot of time.

What not to do

  • Do you have a whole house fan in your home? If so, do not operate a whole house fan during the test.
  • Do not put your test in a crawl space, closet, kitchen, laundry room, or bathroom.
  • Do not put your test near any exterior doors, windows, or walls.
  • Do not put your test on a granite countertop or slate-top pool table.
  • Do not put your test near air vents, fans, or direct sunlight.
  • Do not put your test in a place that can be easily disturbed by children or pets.
  • Do not run your test for less than 2 days (48 hours).
  • Do not wait more than a day to ship your test to the lab.

Tips for success

  • Take a picture of your kit serial number, the white barcoded sticker on the clear tray of the test kit. You’ll need the serial number to complete your registration and get your results.
  • Make a note of the start time of your test and the end time of your test. Be specific-–write down the date and time down to the hour and minute!

Home buyers are encouraged to test for radon during the inspection process of a real estate transaction.

Hire a licensed radon measurement professional to conduct a short term radon measurement using a professional-grade Continuous Radon Monitor or other approved test device.

If elevated levels of radon are present, work with the seller to get a radon mitigation system installed.

Read the CDPHE Radon and Real Estate and Rental Transactions brochure to learn more. 

Tenants are allowed to test their own units for radon under Colorado law.

As of August 7, 2023, landlords in Colorado are required to disclose radon information when a tenant signs a lease agreement. Tenants can void their lease if the landlord does not include the radon disclosure or if a landlord does not make reasonable efforts to mitigate elevated radon levels after 180 days. Learn more about landlord's responsibilities in SB23-206a.

EPA renters guide for tenants

Licensed Radon Measurement and Mitigation Professionals 

Disclaimer: CDPHE does not accredit, certify, license, recommend or endorse listed individuals or companies, nor are we responsible for work done or liability incurred by residents. Listed contractors are certified by the National Radon Proficiency Program or the National Radon Safety Board, and must be licensed by the Colorado Department of Regulatory Agencies.

If the contractor is certified with the National Radon Proficiency Program, file a complaint directly with the National Radon Proficiency Program.


If the contractor is certified with the National Radon Safety Board, file a complaint directly with the National Radon Safety Board.


If the contractor is licensed, or not licensed, by the Colorado Department of Regulatory Agencies (DORA), file a complaint directly with the Colorado Department of Regulatory Agencies.

Mitigating your home for radon

Radon mitigation systems are the best way to reduce elevated levels of radon in a home or building. These systems typically reduce levels by preventing radon from entering the building, but they can also reduce radon levels by diluting indoor air with outdoor fresh air.
 
The most effective solution is usually a sub-slab (or if you have a crawl space, sub-membrane) depressurization system.

A mitigation system in Colorado usually costs about $1,000 - $2,000 unless difficult design problems are encountered.

You might be able to do sub-slab depressurization yourself if you have good handyman skills, including electrical wiring skills.

While caulking and sealing are done as part of the mitigation process, the purpose isn’t to keep radon out but to hold conditioned air in. It’s impossible to seal all cracks and the task is time-consuming, expensive and temporary (sealant dries out over time). This procedure isn’t recommended as a stand-alone technique.

Certified Radon Measurement and Mitigation Contractors

Disclaimer: CDPHE does not accredit, certify, license, recommend or endorse listed individuals or companies, nor are we responsible for work done or liability incurred by residents. Listed contractors are certified by the National Radon Proficiency Program or the National Radon Safety Board, and must be licensed by the Colorado Department of Regulatory Agencies.

If the contractor is certified with the National Radon Proficiency Program, file a complaint directly with the National Radon Proficiency Program.

If the contractor is certified with the National Radon Safety Board, file a complaint directly with the National Radon Safety Board.

If the contractor is licensed, or not licensed, by the Colorado Department of Regulatory Agencies (DORA), file a complaint directly with the Colorado Department of Regulatory Agencies.

  • Mitigation overview.
    • A short 10 minute video clip showing installation of common elements of radon mitigation systems.
  • Live classroom delivery.
    • A Do-It-Yourself course for homeowners interested in mitigating their homes or becoming informed consumers before hiring a contractor.
  • Radon mitigation equipment.
    • A guided tour of a mitigation supply house with an in depth discussion of mitigation system components and how they are used.​​
  • While caulking and sealing are done as part of the mitigation process, the purpose isn’t to keep radon out but to hold conditioned air in.
    • It’s impossible to seal all cracks and the task is time-consuming, expensive and temporary (sealant dries out over time).
    • This procedure isn’t recommended as a stand-alone technique.

Radon in water

If your water comes from a private well and you found a radon problem when you tested the air in your home, you should also test the water.

Radon and water testing kits are available online and at most home improvement stores.

Radon in water mitigation companies in Colorado – Updated 5/4/2024