Radon Testing in Denver, CO: EPA Zone 1 Risk, Certified Contractors & Costs
Denver sits at 5,280 feet above sea level. That elevation matters for radon. Lower atmospheric pressure at altitude means radon gas encounters less resistance as it migrates from soil into homes — and once inside, it accumulates faster than at sea level. Combined with Colorado’s uranium-rich granitic geology along the Front Range, Denver has some of the highest average indoor radon levels of any major U.S. city.
The EPA classifies Denver County — and most of the greater Denver metro area — as Radon Zone 1, the highest risk designation, where average indoor radon levels are predicted to exceed 4 pCi/L. The Colorado Department of Public Health and Environment (CDPHE) estimates that nearly 50% of Colorado homes tested have radon at or above the EPA action level.
That is not a small number. If you have not tested your Denver home, the statistical odds favor elevated radon.
Why Radon Testing Matters in Denver
Radon is odorless and invisible. You cannot detect it without a test. The EPA estimates radon causes approximately 21,000 lung cancer deaths per year in the United States — it is the second leading cause of lung cancer after cigarette smoking.
Denver-specific factors that increase risk:
- Elevation: At 5,280 ft, lower barometric pressure accelerates radon entry into buildings
- Geology: The Rocky Mountain Front Range is underlain by uranium-bearing granite and metamorphic rock — radon’s primary source material
- Home construction: Many Denver-area homes have basements or crawl spaces, which are the primary radon entry points
- Seasonal sealing: Cold Colorado winters mean tight, sealed homes with minimal ventilation — radon levels are typically highest November through March
Testing is the only way to know your actual exposure level. The EPA recommends all homes below the third floor be tested, regardless of location.
How Radon Testing Works in Denver
Short-Term Test (2–7 Days)
The fastest screening option. A charcoal canister or continuous radon monitor is placed in the lowest livable level of your home under closed-house conditions (windows and exterior doors closed for 12 hours before and during the test). Results are available within a few days of sending the device to a lab.
- DIY kit: $15–$40, available at hardware stores and online
- Professional short-term test: $150–$250 from a certified Colorado contractor
Long-Term Test (90 Days–1 Year)
Uses an alpha track detector. Provides a time-averaged reading that accounts for Denver’s seasonal variation (levels are typically higher in winter). More reliable for annual average assessment and post-mitigation confirmation.
Real Estate Testing
Radon testing is standard in Denver real estate transactions. Colorado law does not mandate it, but buyers routinely include radon testing as a contingency. Sellers who have already tested and mitigated are in a measurably stronger negotiating position. Results are typically required within 48–72 hours — always use an NRPP or NRSB certified professional for real estate tests.
Understanding Your Denver Radon Test Results
| Radon Level | What It Means | Recommended Action |
|---|---|---|
| Below 2 pCi/L | Low risk | No action needed; retest every 2–5 years |
| 2.0–3.9 pCi/L | Moderate risk | Consider mitigation; confirm with long-term test |
| 4.0 pCi/L and above | EPA action level | Mitigation recommended |
| 8.0 pCi/L and above | High risk | Mitigate as soon as possible |
The EPA’s action level of 4.0 pCi/L is a risk threshold, not a safe level. For Denver homes in Zone 1, mitigation at any level above 2.0 pCi/L is worth discussing with a certified contractor.
Radon Mitigation in Denver: Methods & Costs
If your test result is 4.0 pCi/L or above, a certified mitigation contractor installs an Active Soil Depressurization (ASD) system — the standard fix for most Denver-area homes. A PVC pipe routes from beneath the foundation slab and exhausts above the roofline. A continuously running fan draws radon from the soil before it can enter the building.
- Standard ASD system (single extraction point): $900–$1,500
- Complex install (multiple entry points, finished basement): $1,500–$2,800
- Post-mitigation re-test: Required; 24–48 hours post-activation
- Annual fan check: Recommended; $75–$125
A correctly installed system reduces indoor radon by 80–99%. Most Denver homes reach sub-2.0 pCi/L after mitigation. For a complete breakdown, see our Radon Testing & Mitigation Guide.
Nearby Denver Communities at Risk
Elevated radon is not limited to the city of Denver proper. All of the following communities fall within or adjacent to EPA Zone 1:
- Aurora — large housing stock with basements; Zone 1
- Lakewood — Jefferson County; Zone 1; older home construction common
- Englewood — Arapahoe County; Zone 1
- Arvada — Jefferson/Adams counties; Zone 1
- Westminster — Adams/Jefferson border; Zone 1
- Thornton — Adams County; Zone 1
- Centennial / Lone Tree — Douglas County; Zone 1
- Littleton — Arapahoe/Jefferson/Douglas; Zone 1
- Commerce City — Adams County; Zone 1
- Brighton — Adams County; Zone 1
Frequently Asked Questions: Radon Testing in Denver
How common is elevated radon in Denver homes?
Very common. CDPHE data shows nearly 50% of Colorado homes tested have radon at or above 4.0 pCi/L. Denver’s elevation and geology put it above the national average. If your home has not been tested in the past two years — or never been tested — assume the risk is real until proven otherwise.
Does elevation affect radon levels in Denver?
Yes. At 5,280 feet, atmospheric pressure is roughly 17% lower than at sea level. Lower pressure means less resistance for radon migrating from soil into the home, and faster indoor accumulation. Denver’s elevation is a genuine risk multiplier on top of already-elevated geological radon sources.
How much does radon testing cost in Denver?
DIY charcoal canister kits run $15–$40. Professional short-term tests cost $150–$250. Long-term testing (90+ days) runs $30–$75 for a mail-in kit. For real estate transactions, professional tests with tamper-resistant monitors typically cost $175–$275.
Does Colorado require radon contractors to be certified?
Colorado requires radon measurement and mitigation professionals to be certified through the NRPP or NRSB. Verify your contractor’s certification at nrpp.info or nrsb.org before hiring. Colorado does not have a separate state licensing board — national certification is the standard.
When is the best time to test for radon in Denver?
Radon levels are typically highest in winter when homes are sealed and heating draws air from below the slab. Testing between October and March gives you the most conservative reading. That said, the EPA recommends testing year-round — any positive result is actionable.
Can I test for radon myself or should I hire a professional?
For initial screening, a DIY charcoal kit is a reasonable first step. For real estate transactions, post-mitigation confirmation, or any result above 4.0 pCi/L, hire a certified professional. Self-test results are not accepted in most real estate transactions in Colorado.
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Sources
- U.S. EPA — A Citizen’s Guide to Radon
- EPA Map of Radon Zones — Colorado
- Colorado CDPHE — Radon Program
- NRPP Contractor Directory
- NRSB Contractor Directory
- World Health Organization — Handbook on Indoor Radon (2009)