Radon Testing Colorado: What Homeowners Need to Know
Radon testing in Colorado is recommended for every home in the state. Colorado is mostly designated EPA Zone 1 — the agency’s highest predicted-screening-level category — and roughly half of all Colorado homes tested through state data exceed the EPA 4 pCi/L action level. Front Range basements frequently test in the 4 to 10 pCi/L range. The state Department of Public Health and Environment (CDPHE) operates a structured radon program, and several county health departments distribute free or low-cost test kits seasonally. This guide summarizes EPA and CDPHE guidance current as of 2026; it does not replace direct consultation with a certified radon professional, and any test result above 4 pCi/L should trigger mitigation planning.
Why Colorado is a high-radon state
Colorado’s geology produces uranium-rich soils across most of the state. The natural decay of uranium produces radon-222, a colorless, odorless, radioactive gas that migrates through soil and accumulates in indoor spaces — particularly basements and lower levels of homes. EPA’s Map of Radon Zones classifies almost all of Colorado as Zone 1 (predicted average indoor screening levels above 4 pCi/L), and CDPHE’s published test data confirms that field results match the prediction. Front Range counties — Denver, Douglas, Elbert, Arapahoe, Jefferson, El Paso, Adams, Boulder, Broomfield — are uniformly Zone 1.
The health framing matters. The EPA attributes roughly 21,000 U.S. lung-cancer deaths per year to radon exposure, making it the leading cause of lung cancer among non-smokers. There is no level of radon exposure considered fully safe; the relationship between exposure and lung-cancer risk is linear with no threshold. The 4 pCi/L EPA action level is a regulatory trigger, not a safety floor.
The CDPHE radon program
The Colorado Department of Public Health and Environment manages the state radon program through its Air Pollution Control Division. The program includes:
- Public education about radon health risks and testing recommendations
- A list of CDPHE-certified radon measurement and mitigation professionals
- Coordination with county health departments on test-kit distribution
- Real estate transaction disclosure guidance
- Building code coordination on radon-resistant new construction (RRNC) features
CDPHE recommends every Colorado home be tested for radon, regardless of age, neighborhood, or whether neighboring homes have tested low. Radon levels can vary substantially between adjacent homes because of differences in foundation construction, soil-gas migration paths, and indoor air flow.
Free or low-cost test kits
Several Colorado counties periodically distribute free or low-cost radon test kits through their public health departments. Programs vary by county and year, but historically have included:
- Tri-County Health Department (Adams, Arapahoe, Douglas counties) — free or low-cost short-term kits
- Jefferson County Public Health — seasonal distribution
- Boulder County Public Health — periodic free-kit programs
- El Paso County Public Health — low-cost kits
- Denver Department of Public Health and Environment — seasonal distribution
Availability changes year to year; the county health department website is the authoritative source for current programs. CDPHE’s radon program also maintains coordination across counties.
How testing actually works in Colorado homes
The EPA’s standard short-term testing protocol applies the same way in Colorado as elsewhere. Key requirements:
- Closed-house conditions for at least 12 hours before the test starts and throughout the test period
- Minimum 48-hour exposure for short-term tests
- Lowest occupied level placement (basement if used as living space, first floor otherwise)
- 20 inches above the floor minimum, 3 feet from exterior walls, away from drafts, sunlight, fans, and high humidity
For longer-term testing, alpha-track detectors run 90 days to a full year and produce annual average data without the closed-house requirement. Colorado’s seasonal variation makes long-term testing particularly useful — winter readings often exceed summer readings due to the negative-pressure dynamics of heated homes in cold weather.
Typical Front Range readings
CDPHE-published data and aggregated industry data suggest the following Front Range patterns:
- Roughly 50% of Colorado homes tested exceed 4 pCi/L
- Front Range basements frequently test in the 4 to 10 pCi/L range
- Some properties measure above 10 pCi/L; readings in the 20 to 30+ pCi/L range occur in a small percentage of homes
- First-floor (non-basement) readings are typically 30% to 70% lower than basement readings in the same home
- Newer construction with radon-resistant features may test lower but is not guaranteed to be below the action level
Front Range mitigation is correspondingly common — sub-slab depressurization installations typically run $1,500 to $3,500 for standard configurations. Our companion guide on Colorado radon mitigation covers the mitigation side in more depth.
Test kit types appropriate for Colorado
The four major consumer test types all work in Colorado:
Charcoal canister (short-term, passive)
Fast, cheap, accurate when properly used. $15 to $35 including lab analysis. Good for initial screening and real estate transactions.
Alpha-track (long-term, passive)
90-day to year-long deployment, produces annual average data. $25 to $45 including lab analysis. Particularly useful in Colorado because of seasonal variation.
Continuous radon monitor (CRM, electronic)
Continuous hour-by-hour data display. $150 to $300 upfront, no per-test cost. Useful for verifying mitigation system performance and tracking seasonal changes over time.
Professional measurement
CDPHE-certified radon measurement professionals provide standardized testing with calibrated equipment and a defensible written report. Cost: $125 to $300 for short-term testing. Used for real estate transactions where a defensible result matters, post-mitigation verification, and complex multi-zone testing.
Real estate transactions and radon in Colorado
Colorado is a real-estate-disclosure state. Sellers who know of elevated radon must disclose. Many Front Range transactions include radon testing during the inspection contingency. Typical sequence:
- Buyer’s inspection includes a 48-hour radon test (typical add-on $150 to $250)
- Test result returns within 24 to 48 hours after exposure period ends
- If above 4 pCi/L, buyer can request either price reduction equal to mitigation cost OR seller-completed mitigation before closing
- If seller completes mitigation, a post-mitigation test verifies system effectiveness before closing
CDPHE-certified mitigators can typically install a system within 7 to 14 days, making the request feasible inside most contract timelines.
Radon-resistant new construction (RRNC)
Colorado’s building code requires passive RRNC features in new construction in many jurisdictions. The features — a sub-slab vent pipe, sealed slab penetrations, vapor barrier under the slab — make active mitigation easier and cheaper if needed later. Passive RRNC alone does not eliminate the need for testing; newer Front Range homes still frequently test above 4 pCi/L and require active mitigation despite the passive features.
Common testing mistakes Colorado homeowners make
- Skipping testing because neighbors tested low. Adjacent homes can have very different radon levels due to foundation differences and soil-gas pathways.
- Testing in the wrong location. Basement utility rooms with high airflow, attics, and garages produce meaningless results.
- Opening windows during the test. Single biggest cause of invalid short-term results.
- Skipping the post-mitigation test. Without verification, there’s no way to know whether the mitigation system actually achieved adequate reduction.
- Assuming new homes don’t need testing. Passive RRNC features help but don’t replace testing.
For more on test placement and protocol, our companion guide on radon home test kit testing protocol walks through the steps in more detail.
Front Range county-by-county notes
All Front Range counties sit in EPA Zone 1. Testing recommendations are uniform across counties — every home, regardless of age or location. Mitigation pricing is consistent across the Front Range, with minor variation by market competition. Boulder County tends to run slightly higher on mitigation quotes; El Paso County (Colorado Springs) tends to run slightly lower. The full radon testing pillar for Front Range homeowners covers the regional picture in more depth.
Schools, workplaces, and rental properties in Colorado
Testing recommendations extend beyond owner-occupied single-family homes. Colorado school districts are encouraged to test classrooms and lower-level occupied spaces, particularly in buildings constructed before radon-resistant features became standard. Workplaces in commercial buildings should be tested as part of indoor air quality assessments. Rental properties have specific considerations — Colorado does not have a statewide landlord-tenant radon disclosure requirement as of 2026, but several local jurisdictions have considered such requirements, and many landlords voluntarily test and disclose. Tenants concerned about radon in a rental can request testing through the landlord or conduct DIY testing in their unit; mitigation responsibility typically falls to the property owner.
What new construction features mean for testing
Colorado building code in many jurisdictions requires passive radon-resistant new construction (RRNC) features: a sub-slab vent pipe (typically 3-inch or 4-inch PVC running from a soil-gas collection point under the slab up through the roof), a continuous polyethylene vapor barrier under the slab, sealing of slab penetrations, and an accessible electrical outlet in the attic for future fan installation. Passive RRNC reduces typical post-construction radon levels but does not eliminate them — newer Front Range homes still test above 4 pCi/L in a meaningful share of cases. The advantage of RRNC is that activating the system (installing a fan in the existing vent pipe) is faster and cheaper than retrofitting a mitigation system from scratch. Testing remains the only way to know whether a new home actually needs the fan added or whether the passive features alone are sufficient.
The cost of testing relative to the cost of doing nothing
A $30 charcoal canister test produces a numerical answer about lung-cancer risk exposure. A $200 long-term alpha-track test produces a seasonally representative number. A $300 to $600 professional measurement produces a defensible result for real estate purposes. Across the full range of testing options, the cost is small. The cost of doing nothing is asymmetric — chronic exposure to elevated radon over decades carries a meaningful lung-cancer risk, with the EPA’s published exposure-risk tables suggesting that lifetime exposure at 8 pCi/L produces roughly 15 lung-cancer deaths per 1,000 people. For smokers the risk multiplier is significantly higher (radon and tobacco smoke act synergistically on lung tissue). Testing is one of the few diligence steps where the spend-to-information ratio is genuinely favorable for nearly every homeowner.
When to call a professional
Every Colorado homeowner should test at least once, preferably with a long-term alpha-track or a CRM that produces seasonally representative data. If the test returns above 4 pCi/L, hire a CDPHE-certified mitigation professional and verify the installation with a post-mitigation test. The Front Range health-cost asymmetry is significant — a $30 test and a $1,500 to $3,500 mitigation system are small spends against the lifetime lung-cancer risk being mitigated.
References
- EPA Radon Overview — U.S. Environmental Protection Agency
- EPA Map of Radon Zones — U.S. EPA
- Colorado Radon Program — Colorado Department of Public Health and Environment
- CDC Radon Information — Centers for Disease Control and Prevention
- Radon and Lung Health — American Lung Association
Colorado Front Range homeowners who want a certified test or a connection to a CDPHE-certified mitigation professional can reach out through our contact page.