How Do You Test Your Denver Home for Radon?

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Radon testing in Denver starts with placing an EPA-approved test kit on the lowest occupied level of your home for 48 hours to several months. Results above 4.0 pCi/L mean you need a mitigation system.

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Why Does Radon Testing Matter Specifically in Denver?

Denver sits in EPA Zone 1 — the highest-risk category for indoor radon. Colorado’s underlying geology, particularly uranium-bearing granite and gneissic bedrock, produces radon gas that migrates upward through soil and into homes through cracks, joints, and foundation gaps.

The statewide average indoor radon level runs around 6.3 pCi/L — well above the EPA’s 4.0 pCi/L action level. We typically see roughly half of homes tested in the Denver metro come back at or above that threshold. That’s not a scare tactic — it’s just what the data shows for this region.

Denver’s climate adds another layer. During winter, homes stay sealed for months. That creates stronger negative pressure indoors, which pulls more soil gas up through the foundation. Summer is the opposite problem — open windows can temporarily lower readings and give a false sense of security. Testing during closed-house conditions gives you the most reliable picture.

If you haven’t tested your home, that’s the logical first step before drawing any conclusions about your risk.

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What Types of Radon Tests Are Available for Denver Homeowners?

Short-term charcoal canister tests are the most common starting point. They’re affordable, widely available, and give you results within a week.

You have three main options: a short-term DIY kit, a long-term DIY kit, or a professional test with a continuous radon monitor (CRM). Each serves a different purpose.

Short-term charcoal canister tests run 2–7 days and cost around $15–$40 at most hardware stores. They require closed-house conditions — windows and exterior doors shut for at least 12 hours before the test begins and throughout the testing period. These are good screening tools but capture a snapshot, not an average.

Long-term tests use alpha track detectors and stay in place for 90 days to a year. They cost roughly $25–$60 for a DIY kit. Because they measure radon across multiple seasons, they’re better at capturing your home’s true average — especially relevant in Denver where levels shift considerably between winter and summer.

Continuous radon monitors (CRMs) like Airthings or Safety Siren models run $150–$300 and provide ongoing measurements you can check from a phone app. These are worth considering if you want year-round visibility, especially after a mitigation system is installed.

Professional testing, where a certified contractor places calibrated equipment and interprets results, typically costs $150–$250 for a short-term test.

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Where Should You Place a Radon Test in Your Denver Home?

Place the test in the lowest regularly occupied level — that means the basement if you use it as a living area, bedroom, or home office.

If your basement is unfinished and nobody spends time there, test on the main floor instead. Radon enters from the ground up, so ground-contact levels always show the highest concentrations. Upper floors are typically lower, but not always zero — especially in homes with open floor plans or central HVAC systems that circulate air throughout the building.

A few placement rules matter for accuracy: keep the test at least 20 inches off the floor, at least 12 inches from exterior walls, and away from windows, doors, and high-airflow areas. Don’t place it in a kitchen, bathroom, laundry room, or anywhere with high humidity. Avoid putting it in a closet or cabinet where air doesn’t circulate.

For homes with multiple foundation types — say, a crawl space on one side and a slab on the other — it’s worth running separate tests in each zone. In our experience, this is common in older Denver neighborhoods like Barnum, Westwood, and parts of Arvada where homes were expanded or remodeled over decades. The readings can vary significantly from one section to another.

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How Do You Read Radon Test Results and What Do They Mean?

Your results will come back as a number measured in picocuries per liter (pCi/L). Below 2.0 is low risk. Above 4.0 means action is needed.

The EPA sets 4.0 pCi/L as the action level — the point where a mitigation system is recommended. Between 2.0 and 4.0 pCi/L, the EPA suggests considering mitigation, particularly if you have children at home or plan to stay long-term. Colorado health officials support that approach.

For Denver homeowners wondering what radon levels actually require mitigation action, the answer involves both the number and your household situation.

One important note for summer testing: open windows during warm months can pull outdoor air in and dilute radon readings. If you ran a test with windows open, your real-world winter levels may run higher. Follow closed-house conditions strictly, or run a long-term test that spans both seasons for a truer average.

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How Much Does Radon Testing Cost in Denver, and How Often Should You Test?

DIY short-term kits cost $15–$40. Professional testing runs $150–$250. Long-term kits fall in the $25–$60 range.

For retesting frequency: if your home has no mitigation system and tests below 4.0 pCi/L, retest every two years. After a mitigation system is installed, test within 24 hours of installation and again annually. Any time you make major changes — finishing a basement, adding an addition, replacing HVAC — retest. Real estate transactions in Colorado now require radon disclosure, so having current test documentation on hand matters.

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When Should You Call a Radon Professional Instead of Testing Yourself?

If your initial test comes back at or above 4.0 pCi/L, get a professional involved before taking any further steps.

A certified contractor will verify your results with calibrated equipment, assess your foundation type, and design a mitigation system suited to your specific home. Colorado requires radon mitigation professionals to be licensed through the Colorado Department of Regulatory Agencies (DORA) — ask to see that credential before hiring anyone.

Other situations where professional involvement makes sense: your results are inconsistent across multiple floors, you’re buying or selling a Denver home and need results that hold up in a transaction, or you’ve retested after mitigation and levels haven’t dropped below 2.0 pCi/L. DIY mitigation kits exist, but improper installation can backfire — creating pressure imbalances that actually pull more radon in. That’s not a risk worth taking at levels above 4.0.

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What Should Denver Homeowners Do Next?

Pick up a short-term test kit this week. Most Denver hardware stores carry EPA-listed charcoal canister kits for under $40. Place it in your lowest occupied level, follow the closed-house protocol, and mail it within 12 hours of removing it from the test location.

If results come back above 2.0 pCi/L, follow up with a long-term test or a continuous monitor before deciding on mitigation. If they come back above 4.0 pCi/L, move to professional assessment within the next few weeks — radon exposure accumulates over time, and Denver’s winters can push levels even higher as homes stay sealed.

For homeowners who want a deeper look at the testing process before getting started, the Denver homeowner radon testing guide covers what to expect and how to interpret results in more detail.

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FAQ

Q: Can I test for radon myself, or do I need a professional?

DIY kits are reliable screening tools approved by the EPA. Short-term charcoal kits cost $15–$40. Use a professional if results come back at or above 4.0 pCi/L or if you’re preparing for a real estate transaction.

Q: How long does a radon test take?

Short-term tests run 2–7 days. Long-term tests stay in place 90 days to a year. Lab results typically return within 1–2 weeks of mailing a charcoal canister kit.

Q: Do new Denver homes need radon testing?

Yes. New construction can have higher radon than older homes depending on foundation type and soil conditions. Radon-resistant construction features help but don’t eliminate the need to test.

Q: Will opening my windows fix a radon problem?

No. Open windows can temporarily dilute readings, but levels return as soon as windows close. A sub-slab depressurization system is the permanent solution for elevated radon.

Q: Does radon testing cover the whole house at once?

One test covers one area. Homes with different foundation types or separate additions may need multiple tests. Place each test in the lowest occupied zone of each section.

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Sources

• U.S. Environmental Protection Agency: A Citizen’s Guide to Radon — test placement, action levels, and test kit guidance
• U.S. Environmental Protection Agency: Home Buyer’s and Seller’s Guide to Radon
• Colorado Department of Public Health and Environment: Radon Program — testing guidelines, contractor licensing, and state average radon data
• Colorado Department of Regulatory Agencies (DORA): Radon professional licensing requirements
• Colorado Geological Survey: Radon in Colorado — geology and radon occurrence
• Colorado Environmental Public Health Tracking: Indoor radon levels and county-level data

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RadonSweep helps Denver homeowners connect with certified radon professionals who know Colorado’s geology, building codes, and testing requirements. If your test results are unclear or above the action level, their network can help you figure out the right next step without any pressure.