Radon Home Inspection: A 2026 Front Range Guide
A radon home inspection answers one specific question: is the indoor radon level in this home above the EPA action threshold of 4.0 pCi/L? For Colorado Front Range buyers, that question matters more than in most U.S. markets because EPA places nearly every Front Range county in Radon Zone 1 — the highest predicted indoor radon designation. This guide summarizes EPA, CDC, and Colorado Department of Public Health and Environment (CDPHE) guidance current as of 2026, walks through how a radon home inspection works, what it costs, and what the result actually means. Consult a licensed radon measurement professional for any actionable decisions about your home.
What is a radon home inspection?
A radon home inspection is a measurement test conducted in the lowest occupied level of a home, typically over 48 to 96 hours, using either a continuous radon monitor (CRM), a charcoal canister, an alpha-track detector, or an electret ion chamber. The result is expressed in picocuries per liter (pCi/L) of air. EPA’s recommended action threshold is 4.0 pCi/L; the agency suggests considering mitigation between 2.0 and 4.0 pCi/L as well.
Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and bedrock. It enters homes through foundation cracks, slab penetrations, sump pits, crawlspaces, and well water. EPA and CDC identify radon as the second leading cause of lung cancer in the United States and the leading cause among non-smokers. The radon testing pillar guide for Colorado homeowners covers the broader context, including why Zone 1 designation matters for Front Range buyers.
When should a radon home inspection happen?
During a real estate transaction, the radon home inspection is typically performed during the inspection contingency window — usually within the first 7–14 days after going under contract. The test runs concurrently with the general home inspection. For purchase-side testing, EPA recommends a short-term test (2–7 days) using a continuous monitor or charcoal canister, with closed-house conditions maintained for at least 12 hours before testing begins.
For owner-occupied homes, EPA recommends testing every two years and after any major foundation work, basement renovation, or HVAC system change. The home inspection radon test guide walks through transaction-specific timing in more detail.
How does a radon home inspection actually work?
Continuous radon monitors (CRMs)
The most common professional method in 2026. A calibrated electronic device records radon levels hour by hour over the test period, producing a time-stamped log that flags any closed-house violations (open doors, weather changes) and provides an average reading. Sun Nuclear, Femto-Tech, and AccuStar are common CRM brands used by licensed measurement professionals.
Charcoal canisters
Lower-cost passive devices that absorb radon over 2–7 days and are then mailed to a lab for analysis. Acceptable for compliance testing under EPA protocol when used properly with closed-house conditions. Result turnaround is typically 5–10 business days after the lab receives the canister.
Alpha-track and electret detectors
Longer-term passive devices used for 90 days to one year. Better at characterizing average household exposure but not suitable for real estate transaction timelines.
Test location
The lowest occupied level of the home. For a finished basement, that’s the basement floor. For a slab-on-grade home, it’s the first floor. The device is placed at least 20 inches above the floor, 4 inches from interior walls, and away from drafts, exterior walls, and direct sunlight.
How much does a radon home inspection cost in 2026?
- Bundled with general home inspection: $125–$200 (most common for real estate transactions)
- Standalone professional radon test: $150–$250
- DIY short-term test kit (charcoal): $20–$45 including lab fee
- DIY long-term test kit (alpha-track): $25–$50 including lab fee
- Consumer continuous monitor (AirThings, Corentium): $150–$300 (purchased once, used indefinitely)
For Front Range real estate transactions, bundling radon with the general home inspection is the dominant pattern. The radon testing cost guide covers the full pricing landscape.
What do radon home inspection results mean?
Below 2.0 pCi/L
EPA considers this an acceptable level for indoor air. No mitigation action is recommended. Retesting every two years is reasonable; testing immediately after major foundation work or renovation is advised.
2.0 to 3.9 pCi/L
EPA suggests considering mitigation in this range. Some buyers negotiate a credit at this level; some sellers preemptively mitigate to remove the issue from the negotiation table. The decision is partly personal risk tolerance and partly market norms.
4.0 pCi/L and above
EPA’s action level. Mitigation is recommended. A standard sub-slab depressurization (SSD) system typically brings indoor radon below 2.0 pCi/L. The radon mitigation cost guide walks through pricing for installation.
High readings (10+ pCi/L)
Not unusual on the Colorado Front Range given Zone 1 designation. Mitigation is strongly recommended and often leads to post-mitigation testing to verify the system is performing as designed. Post-mitigation tests typically target levels below 2.0 pCi/L.
Why Front Range homes need radon home inspections
EPA’s Radon Zone Map places Adams, Arapahoe, Boulder, Broomfield, Denver, Douglas, El Paso, Elbert, and Jefferson counties — essentially the entire Front Range — in Zone 1, the highest predicted indoor radon designation. CDPHE estimates roughly half of Colorado homes have radon levels above 4.0 pCi/L. The geology is straightforward: uranium-rich Pikes Peak granite and other Front Range bedrock formations produce more radon than the U.S. average.
That doesn’t mean every Front Range home tests high. Test results vary house-by-house even on the same street, depending on foundation type, soil porosity, HVAC characteristics, and how tightly the home is sealed. The only way to know is to test. The EPA radon zones explainer covers what zone designations mean in practice.
What’s the difference between a real estate radon home inspection and a homeowner radon test?
The protocols differ in a few important ways:
- Closed-house conditions: real estate testing requires 12+ hours of closed-house conditions before and during the test. Owner testing follows the same protocol for accuracy but is less strictly enforced.
- Test location: real estate tests use the lowest occupied level; owner tests can be placed wherever the homeowner spends most time.
- Device tampering detection: licensed measurement professionals use CRMs that log every closed-house violation, ensuring buyers can verify the test was not gamed.
- Documentation: a real estate inspection produces a formal report with the device serial number, calibration date, measurement protocol, and time-stamped log.
For ongoing owner monitoring, consumer CRMs from AirThings or Corentium are reasonable. The AirThings vs Corentium comparison covers consumer-grade options.
What to do with a high radon home inspection result
If the result is at or above 4.0 pCi/L:
- Verify with a second test if results are borderline. Levels can fluctuate seasonally. A confirmatory test using a different method is reasonable for results in the 4.0–5.0 range.
- Consult a licensed radon mitigation contractor. Most states require certification; Colorado uses NRPP and NRSB credentials. Get two or three quotes.
- Negotiate during the contingency window. Buyers commonly request that sellers install a mitigation system before closing, or provide a credit toward post-closing installation.
- Plan for post-mitigation testing. EPA recommends a follow-up test 24 hours to 30 days after mitigation system commissioning to verify the system is performing.
Most homes can be mitigated for $1,200–$2,500 in 2026 dollars. The radon mitigation system guide walks through how SSD systems work. The InspectandTest editorial methodology page covers how we frame mitigation decisions for health-adjacent topics.
Common questions about the radon home inspection process
Does the radon test interfere with the rest of the home inspection?
No. The continuous radon monitor or charcoal canister sits in the lowest occupied level for the test duration, typically untouched. The general home inspection proceeds in parallel and ends before the radon test concludes. Most inspectors return after 48 hours to retrieve the monitor and log the results.
What happens if someone opens a window during the test?
Continuous monitors log every closed-house violation. If a window is opened, the inspector can identify the period of violation and either discount that data or recommend retesting. Charcoal canisters don’t log violations, but a result that seems inconsistent with the home’s profile may warrant retesting.
Can the seller refuse a radon test during the inspection contingency?
Typically no, because radon testing is a standard inspection contingency in most Colorado real estate contracts. Sellers who refuse risk the contract being voided by the buyer. The exception is for tests that require destructive access or extended duration beyond the contingency window.
Is one radon test enough to make a mitigation decision?
For real estate purposes, one EPA-protocol short-term test from a licensed measurement professional is usually enough to trigger or skip mitigation. For owner-occupied homes already past closing, a confirmatory test before spending $1,200–$2,500 on mitigation is reasonable, particularly if the initial result was borderline.
Does radon mitigation reduce home value?
The opposite is more common. An installed and verified mitigation system is often a selling point because it demonstrates the home tested above 4.0 pCi/L and was addressed. Buyers in Zone 1 markets generally view an active mitigation system more favorably than an untested home with unknown levels.
References
- EPA Radon Program — Environmental Protection Agency
- CDC Radon Page — Centers for Disease Control and Prevention
- CDPHE Radon Program — Colorado Department of Public Health and Environment
- EPA Radon Zone Map — Environmental Protection Agency
Front Range buyers wanting a licensed radon measurement professional to test their pre-purchase home can reach out through our contact page for a referral to a vetted local inspector.