Whats a Radon Inspection: A Plain-Language Guide
Whats a radon inspection, in plain terms? It is a measurement service that captures indoor radon concentration over a defined sampling period, typically performed by a certified radon professional during a real-estate transaction or after a homeowner becomes concerned about indoor air quality. The word “inspection” is sometimes used interchangeably with “test” in casual conversation, but the inspection framing implies a professional service with calibrated equipment, formal documentation, and EPA-protocol sampling. This guide explains how the inspection differs from a homeowner test kit, when each is appropriate, and what to expect during a Front Range inspection. Content reflects EPA, CDPHE, and lung-health guidance current as of 2026 — engage a certified radon professional for transaction or mitigation decisions.
Whats a Radon Inspection in Real-Estate Terms
In real-estate transactions, a radon inspection is one of the optional add-on services buyers order alongside the general home inspection. The radon inspector arrives separately, places one or two continuous radon monitors (CRMs) in the lowest livable level of the home, programs them for 48 hours of measurement, and returns to retrieve the devices and download the data. The result is a printed report showing hourly readings over the test period, an average radon concentration in picocuries per liter (pCi/L), and a recommendation: results above 4 pCi/L typically trigger a mitigation discussion in the contract; results between 2 and 4 pCi/L may also warrant action depending on the buyer’s risk tolerance.
The inspector documents the closed-house conditions, the device serial numbers, the start and end times, and the location of placement. The documentation matters because mitigation contractors and EPA protocols require chain-of-data integrity. A homeowner-collected charcoal canister result does not carry the same weight in a transaction.
Radon Inspection Versus Radon Testing
The terms get used interchangeably but the difference is meaningful. “Radon testing” is the broader category, covering everything from a $20 charcoal canister mailed to a lab to a professional CRM deployment. “Radon inspection” implies a professional service with formal documentation. The EPA’s residential radon protocol is the underlying standard for both.
For Front Range homeowners, the practical distinction matters in three contexts. In a real-estate transaction, the inspection is what counts because lenders and sellers want documented results. In homeowner curiosity about indoor air quality, a self-test kit is usually sufficient. In post-mitigation verification, a professional inspection with a CRM is the standard because the result will be used to confirm whether the mitigation system is performing.
How Long an Inspection Takes
EPA’s residential measurement protocol calls for a minimum of 48 hours of closed-house sampling. The inspector typically arrives on day one, places the device, leaves a closed-house instruction card with the occupants, and returns on day three to retrieve the device. The closed-house protocol requires keeping windows shut, exterior doors closed except for normal entry and exit, and the HVAC system running in its normal mode for that time of year.
Some inspectors run 72-hour or longer tests, particularly for high-stakes transactions or for confirming borderline results. The protocol allows shorter durations down to 48 hours minimum, and longer durations always improve precision. The inspection report includes the actual measurement period and any deviations from the protocol.
Why Colorado Buyers Almost Always Order the Inspection
Colorado sits in EPA’s Zone 1, the highest-risk zone in the national radon potential map. Roughly half of homes tested in Colorado exceed the 4 pCi/L action level, with some counties showing exceedance rates above 60 percent. The geology — uranium-bearing granite under much of the Front Range, plus the radium-rich soils common across the state — produces sustained radon entry into buildings through foundation cracks, sump pits, and slab penetrations.
Because the Zone 1 base rate is so high, Front Range buyers who waive radon inspection accept a coin-flip risk on a $1,200 to $2,000 mitigation expense after closing. Most buyers add the $150 to $200 inspection during the contract-to-close window and use the result to negotiate mitigation as a seller responsibility before closing. See the broader radon testing in Colorado guide for the regional risk picture.
What the Inspector Brings to the Job
A continuous radon monitor is the workhorse instrument for professional inspections. The device measures radon by ionization or alpha-track counting at hourly intervals and stores the data internally until downloaded. Cost for the inspector to buy the device runs $700 to $1,500 per unit, with annual calibration and quality-control checks required to maintain certification. Some inspectors carry two units to deploy in parallel for cross-verification.
The inspector also brings closed-house instruction cards for occupants, chain-of-custody forms, and documentation tools to record placement conditions. A photo of the placement location with a timestamp is standard practice. The deliverable at the end is a formal report with the data, the placement documentation, and the inspector’s certification number.
EPA Action Levels and What They Mean
EPA’s residential radon guidance establishes two thresholds. At 4 pCi/L, the agency recommends mitigation. Between 2 and 4 pCi/L, the agency notes that homeowners should consider mitigation, particularly if they spend a lot of time in lower levels of the home. Below 2 pCi/L, no action is recommended but periodic re-testing is encouraged because radon levels can change over time due to seasonal patterns and structural changes.
The action levels are not bright-line health thresholds. The World Health Organization recommends mitigation at 2.7 pCi/L. Long-term occupational exposure standards from OSHA and similar agencies use different thresholds because the exposure duration assumption is different. For residential context, EPA’s 4 pCi/L is the standard most U.S. inspectors and mitigators reference.
What Happens After the Inspection
A result above 4 pCi/L triggers a mitigation discussion. The buyer can request the seller install a mitigation system before closing, request a credit at closing to cover the cost, or proceed with closing and handle mitigation as a post-closing project. Most Front Range contracts use one of the first two options because the leverage exists during the inspection objection period.
A result between 2 and 4 pCi/L is a judgment call. Some buyers ask for partial credit; others accept the result and plan to retest after closing. A result below 2 pCi/L typically closes the radon discussion for the transaction. The radon test inspection overview walks through the post-result decision tree.
Cost of the Inspection
Standalone radon inspection in the Denver metro runs $150 to $200. Bundled with a general home inspection, the radon add-on typically drops to $135 to $175. Mountain communities and outlying counties carry a small travel premium. Post-mitigation verification inspections — performed after a mitigation system is installed — run the same price as initial inspections and are required by most mitigation contractors to confirm system performance.
The cost is small relative to the alternative. A mitigation system in a typical Front Range home costs $1,200 to $2,000 installed. Negotiating that cost as a seller responsibility during the contract objection period transfers the entire mitigation expense to the seller in exchange for the $175 inspection fee.
Self-Test Kits Versus Professional Inspections
Self-test kits work for homeowner-driven indoor air-quality concerns and for compliance with state-mandated testing in some jurisdictions. Charcoal canisters cost $15 to $30 plus lab fees. Alpha-track detectors for long-term measurement cost $25 to $50. Digital monitors for ongoing measurement cost $130 to $200 for consumer-grade devices.
Self-tests are not generally accepted for real-estate transactions because the chain-of-custody is not formal. The lab returning the canister result has no way to verify the canister was actually deployed in the lowest livable level of the property under closed-house conditions. Professional inspections solve this by having the certified inspector handle the entire process.
Re-Testing Frequency
EPA recommends re-testing every two years in homes with prior readings near or above the action level. Re-testing after major renovations — foundation work, basement finishing, HVAC replacement — is also recommended because structural changes affect radon entry pathways. Homes with installed mitigation systems should be re-tested every two years to verify the system continues to perform. CDPHE publishes similar re-testing guidance for Colorado homeowners.
Why the Term “Inspection” Matters in Documentation
The word choice on the report has consequences. Lender requirements for radon mitigation in some markets specify a “radon inspection by a certified professional,” not just a “radon test.” The distinction is bureaucratic but real. When seeking to attach a mitigation requirement to a transaction, a formal inspection report with the inspector’s certification number satisfies the documentation. A self-test result may not. The radon house inspection guide covers the documentation framework in depth.
Choosing Between Stand-Alone and Bundled Inspections
Buyers in real-estate transactions can either book the radon inspection separately from the general home inspection or bundle the two services. Bundling typically saves $25 to $50 on the radon component because the inspector is already on site. Stand-alone radon inspections make sense when the buyer wants a different specialist for the radon work, when the general home inspection is already booked with a firm that does not offer radon testing, or when post-mitigation verification testing is needed without a full home inspection.
The decision rarely changes the quality of the result. Both bundled and stand-alone services use the same continuous radon monitor hardware, follow the same EPA protocol, and produce the same report format. The cost difference is the main practical variable. The can you test for radon yourself guide covers the homeowner DIY alternative.
Seasonal Considerations on the Front Range
Front Range radon readings often run higher in winter than summer because heating-season stack effect pulls more soil gas through the foundation. A summer test that returns 3.2 pCi/L could read 5.0 pCi/L in February when the same home is operating with the furnace running and windows closed for weeks. EPA’s residential protocol allows testing year-round, but inspectors who test in summer sometimes recommend a winter follow-up if the result is near the action threshold. Buyers in the contract objection period during summer should keep this seasonal pattern in mind when evaluating borderline results, and consider negotiating an inspection contingency that extends through a winter retest if timing allows.
What to Do If the Inspector Recommends Mitigation
A result above the EPA action level triggers a mitigation recommendation in the inspection report. The next step is engaging a certified radon mitigation contractor. Most certified inspectors maintain referral lists of qualified mitigation contractors but typically do not perform mitigation themselves to avoid the conflict-of-interest concern. The mitigation contractor performs a diagnostic walk-through, designs a system specific to the home’s foundation and HVAC configuration, installs the system over one to two days, and verifies post-installation performance with a follow-up test.
System design varies. Active sub-slab depressurization is the dominant approach for slab-on-grade and basement homes. Sub-membrane depressurization works for crawlspaces. Aggressive sealing of major entry points often accompanies the active system. The mitigation contractor should provide a written warranty on the installation and the system’s ability to reduce radon below the action level. The how to check for radon in your house guide covers the post-test response framework.
References
- EPA radon program — U.S. Environmental Protection Agency
- CDPHE radon program — Colorado Department of Public Health and Environment
- American Lung Association radon resources — American Lung Association
- CDC radon information — Centers for Disease Control and Prevention
Front Range buyers and sellers planning a radon inspection during a real-estate transaction can reach out through our contact page for a referral to a certified radon professional.