A radon contractor is not a single job title. Colorado treats measurement (testing) and mitigation (fixing) as related but distinct services, and the state health department's contractor information describes separate certification routes through the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB), plus licensing by the Colorado Department of Regulatory Agencies (DORA). Before you compare anyone, confirm which service you need: a test you can trust, a system design for an existing home, or a check on a system you already own.
One caution from the outset: the Colorado Department of Public Health and Environment (CDPHE) states plainly that it does not accredit, certify, license, recommend or endorse listed individuals or companies. Any list you find, including one on a state page, is a starting point for verification, not a badge of quality. Ask the questions below and write down the answers.
Start with credentials and scope
Begin every conversation with three short questions. Which certification bodies currently credential the person or firm, and for measurement, mitigation, or both? What is their DORA license status? And who will physically be on site, since the person who answers the phone may not be the person doing the work.
CDPHE's own complaint guidance is a useful map of accountability. If a concern involves certification with NRPP, the state directs complaints there; if it involves NRSB certification, complaints go to NRSB; and if it involves state licensing with DORA, complaints go to DORA. Knowing this before you hire tells you what recourse actually exists afterward. Ask each provider to identify in writing which of those bodies they answer to.
What the test will look like
If you are hiring a measurement professional, ask how the test will be conducted and where the device will go. CDPHE relays EPA placement guidance for two different purposes. To decide whether your home warrants mitigation, EPA recommends testing in the lowest living area. For a real estate transaction, EPA recommends testing in the lowest area that could be modified into living space, such as an unfinished basement. Those can be different rooms, and the answer should match your reason for testing.
Ask how long the test runs. CDPHE describes short-term tests as taking 48 to 120 hours: the house is closed for 12 hours, the device is then activated and left in place for at least 48 hours. Long-term tests run 91 days to a year under normal living conditions and CDPHE describes them as giving a more representative picture over time. A professional who cannot explain which type they are using, and why, has not answered the question.
Also ask what conditions they require. CDPHE instructs residents to keep exterior doors and windows closed for the duration and to avoid operating a whole house fan during the test. Follow the instructions packaged with whatever device is used, since kit and device protocols can differ at the edges.
Questions about the fix itself
If your results point toward mitigation, the conversation shifts to design. CDPHE states that the most effective solution is usually a sub-slab depressurization system, or a sub-membrane system where there is a crawl space. Ask which approach is proposed for your house and what specific feature of your foundation, crawl space, or drainage led to that choice.
A frequent misconception is that sealing cracks is the cure. CDPHE explains that caulking and sealing are done as part of mitigation, but the purpose is to hold conditioned air in, not to keep radon out, and it is not recommended as a stand-alone technique. If a proposal is mostly sealant, you have a concrete question to ask about what else is being done.
Ask about expectations and verification. EPA states that radon reduction systems can reduce a home's radon levels by up to 99%, which is a documented upper bound, not a promise for your house. Ask what post-installation testing is planned, who performs it, and when. Then ask about the retest rhythm: CDPHE advises homeowners who already have mitigation systems to retest every two years, and EPA guidance calls for testing at least every two years to verify that a mitigation system remains effective. Ask who you call if a retest shows levels creeping back up.
Example: comparing three proposals (hypothetical)
The following is an illustration, not advice about a specific property. Suppose a homeowner opens a crawl space and finds three bids. Bid A lists an NRPP certification number and a DORA license, proposes a sub-membrane depressurization system, and includes a post-installation test date. Bid B emphasizes sealing every visible crack and does not name a certification body. Bid C is the cheapest but cannot say which organization would hear a complaint.
Read against the guidance above, Bid A answers the scope question, matches CDPHE's description of the usual effective approach, and builds in verification. Bid B leaves the stand-alone sealing question unresolved. Bid C fails a recourse question you can answer today. None of this proves Bid A will perform best. It does show that the questions sorted the proposals by how completely each one answered them.
Cost and assistance questions
CDPHE describes a typical Colorado mitigation cost of about $1,000 to $2,000 unless difficult design problems are encountered. Treat that as general context for planning, not a quote; actual pricing depends on the home and should come to you in writing.
Ask directly whether any assistance program applies to your situation. CDPHE offers a Low-Income Radon Mitigation Assistance program for homeowners who qualify through an application process and reported mitigating over 200 homes through it in 2025. Eligibility and current status should be confirmed with CDPHE, not inferred from a contractor's pitch. If your water comes from a private well and an air test found a problem, CDPHE also advises testing the water.
What to do next
Before you call anyone, settle two facts on paper: your most recent test result and where in the home the device sat. Then write down your questions and the answers, with dates and names. If you have a current result and want to decide whether to test again, retest, or seek a mitigation proposal, start with our guide on using official guidance to plan your next step. To prepare for a call, review the parts of a mitigation system so the design discussion is easier to follow, and keep your notes on the private record and questions sheet. For direct official resources, consult CDPHE's testing and mitigation page and the EPA's National Radon Action Month guidance.
