—
Radon test results are measured in picocuries per liter (pCi/L). In Denver, any result at or above 4.0 pCi/L means you need mitigation. Results between 2.0 and 4.0 pCi/L warrant a follow-up test or serious consideration of action.
—
Why Radon Test Results Hit Differently in Denver
Denver sits in EPA Zone 1 — the highest radon potential classification on the map. Colorado’s bedrock is laced with uranium-bearing granite and gneissic formations, and as that uranium breaks down underground, radon gas rises through the soil and into homes. The statewide indoor radon average sits around 6.3 pCi/L, which is well above the EPA’s 4.0 pCi/L action level.
This fall, as Denver homes seal up against cooling temperatures, radon concentrations tend to climb. The stack effect — where warm indoor air rises and pulls soil gases upward through foundation cracks — grows stronger as heating systems run longer. That’s why testing before winter is worth prioritizing, not putting off.
In the Denver metro, roughly half the homes we test come back above the action level. The Front Range geology and tight construction in newer neighborhoods both contribute to that pattern. Understanding what your specific number means is the first step toward protecting your household.
—
What Do the Numbers on a Radon Test Actually Mean?
A radon test result is a concentration measurement — how many radioactive particles are breaking down per liter of air in your home every minute.
The EPA action level is 4.0 pCi/L. Below 2.0 pCi/L is generally considered low risk. The range between 2.0 and 4.0 pCi/L is a gray zone where the health risk is real but mitigation is a judgment call based on your household’s situation. Above 4.0 pCi/L, mitigation is the clear recommendation — not a maybe.
Radon exposure is cumulative. A result of 8.0 pCi/L isn’t twice as concerning as 4.0 pCi/L in a casual sense — it represents meaningfully greater long-term lung cancer risk the longer you remain exposed without acting. Colorado’s radon-related lung cancer deaths number around 500 per year, making it the leading cause of lung cancer in non-smokers statewide.
One number from one test is a snapshot, not a complete picture. Levels shift with seasons, weather patterns, and how often windows are open. That context matters when you’re deciding what to do next.
—
Which Type of Test Produced Your Result — and Does It Matter?
Short-term tests (charcoal canisters, 2–7 days) and long-term tests (90 days to a year) produce different kinds of data, and the distinction affects how you interpret your result.
A short-term charcoal canister test, which costs around $15–$40 as a DIY kit or $150–$250 through a professional, gives you a quick snapshot. It’s an EPA-approved screening tool, but it captures conditions during a specific window — including any unusual weather or ventilation patterns during that period. If your short-term result comes back elevated, a follow-up long-term test or a professional radon assessment is the right move before committing to mitigation.
Long-term tests average out seasonal swings and give a more accurate picture of what your household is actually breathing year-round. They typically run $25–$60 as DIY kits.
Continuous radon monitors (CRMs) — devices like Airthings units, priced around $150–$300 — provide ongoing readings with hour-by-hour data. These are useful after mitigation to confirm a system is working, or for homeowners who want to track patterns over time rather than rely on a single test window.
—
How Should You Interpret Results If You Have a Mitigation System?
If your home already has a sub-slab depressurization system installed, a post-mitigation test result changes the conversation.
A well-functioning system should bring levels below 2.0 pCi/L in most Denver homes. If a post-mitigation test still shows levels above 2.0 pCi/L — and especially anything approaching 4.0 pCi/L — that’s a signal the system may be undersized, the suction point may be poorly placed, or there’s a pathway the system isn’t capturing. We typically see this in homes with complex slab configurations or where a DIY system was installed without proper diagnostic testing.
Annual maintenance on a mitigation system runs between $0 and $150 depending on whether you’re doing a basic U-tube manometer check yourself or having a professional inspect the fan and pressure field. Most systems use a fan that lasts 5–10 years before needing replacement.
If your result after mitigation is still elevated, schedule a diagnostic inspection — not just a retest. The issue is usually mechanical and fixable, but it needs someone who can read the system’s pressure field, not just swap in a new fan.
—
What Results Should Trigger Immediate Professional Contact?
Any result at or above 4.0 pCi/L calls for professional mitigation, ideally scheduled within a few months. Results above 8.0 pCi/L warrant faster action — within weeks, not the next calendar year.
Above 20.0 pCi/L is uncommon but not rare in certain Denver-area soil conditions. At that level, treat it as urgent. Most licensed contractors in the metro can schedule an initial assessment within a few business days, and installation of a standard sub-slab depressurization system typically takes four to six hours for a straightforward job.
For a clearer picture of what levels require mitigation in Denver homes, the thresholds below give a practical framework.
Colorado requires radon professionals to hold licensure through DORA (Department of Regulatory Agencies). Always confirm your contractor is licensed before work begins — particularly for results above 4.0 pCi/L, where proper system design matters significantly.
—
How Do Radon Test Results Compare Across Testing Methods?
| Test Type | Duration | Cost (DIY) | Cost (Pro) | Best Use |
|---|---|---|---|---|
| Charcoal Canister (Short-Term) | 2–7 days | $15–$40 | $150–$250 | Initial screening |
| Alpha Track (Long-Term) | 90 days–1 year | $25–$60 | Included w/ service | Accurate annual average |
| Continuous Radon Monitor | Ongoing | $150–$300 | N/A (purchase) | Post-mitigation tracking |
| Professional CRM Test | 48–96 hours | N/A | $150–$250 | Real estate transactions |
—
When Is a Professional the Right Call?
A DIY test kit is a reasonable starting point. A licensed professional becomes necessary in these situations:
- Your result is at or above 4.0 pCi/L on any test type
- You’re buying or selling a home — Colorado requires radon disclosure in real estate transactions
- Results vary widely between floors or rooms, suggesting a complex entry pathway
- You have a mitigation system and post-mitigation levels are still elevated
- Your home has a sump pit, crawl space, or exposed soil, which complicate DIY mitigation
Don’t attempt to fix elevated radon with ventilation alone. Opening windows drops levels temporarily — levels return once windows close, and that approach offers no reliable protection during Denver’s sealed-up winter months.
—
What Should Denver Homeowners Do Next?
If you haven’t tested yet, start with a short-term charcoal canister test placed in the lowest regularly occupied level of your home. Follow closed-house conditions for 48 hours before and during the test. Fall is a good time — conditions reflect what your home will do through the heating season.
If your result is below 2.0 pCi/L, retest every two years or after major renovations. Between 2.0 and 4.0 pCi/L, run a long-term test to confirm the average before deciding on mitigation. At 4.0 pCi/L or above, contact a DORA-licensed radon contractor and discuss system options. Mitigation in Denver typically runs $800–$2,500, with most residential installs falling around $1,200.
Keep copies of all test results. You’ll need them for real estate disclosures, and they establish a baseline if you test again after renovations or system installation.
—
FAQ
Q: What is a safe radon level for a Denver home?
The EPA considers below 2.0 pCi/L low risk. Denver’s average is well above that, so testing is essential — not optional.
Q: How long does a radon test take before I get results?
Short-term charcoal tests take 2–7 days of exposure, then lab processing of 2–5 business days. Professional CRM tests can produce results within 48–96 hours.
Q: Can radon levels change significantly from one test to the next?
Yes. Seasonal shifts, weather pressure, and ventilation all affect readings. A single short-term result is a screening tool — follow up with a long-term test if results are elevated.
Q: Do new homes in Denver have lower radon levels?
Not necessarily. Newer construction can actually concentrate radon more efficiently due to tighter building envelopes. Construction type matters more than age.
Q: How soon after mitigation should I retest?
Wait 24 hours after installation, then run a short-term test. Most contractors recommend retesting 30 days post-installation for a reliable post-mitigation baseline.
—
Sources
- U.S. Environmental Protection Agency: Radon action levels, testing guidance, and mitigation recommendations
- Colorado Department of Public Health and Environment: Radon FAQ, state average radon levels, and mitigation guidelines
- Colorado Geological Survey: Uranium-bearing geology and radon occurrence in Colorado
- Colorado Department of Regulatory Agencies (DORA): Radon professional licensing requirements
- Colorado Environmental Public Health Tracking: Radon-related lung cancer statistics and real estate disclosure requirements
—
RadonSweep connects Denver homeowners with certified radon professionals who understand Colorado’s specific soil conditions and building codes. If your test results raised questions — or if you haven’t tested yet heading into winter — their network of licensed contractors can help you figure out exactly where you stand and what, if anything, needs to happen next.