How to Test Your Home for Radon: A Plain-Language Guide
How to test your home for radon is one of the simplest health-protective tasks a Colorado homeowner can perform. The Front Range sits squarely in EPA Zone 1, where geology produces elevated radon risk across most counties, and a short-term test kit costs less than a tank of gas. This guide walks through kit selection, where to place the detector, how long to run the test, what the lab report means, and what to do at each result level. EPA, CDC, and Colorado Department of Public Health and Environment guidance current as of 2026 underpins the recommendations.
Why every Front Range home should test
The EPA map classifies Colorado as Zone 1 — the highest-risk zone — for radon, summarized at the EPA radon program page. The Colorado Department of Public Health and Environment’s own radon program estimates roughly half of Colorado homes test above the EPA action level of 4.0 picocuries per liter (pCi/L). The state’s data is published at the CDPHE radon program page. Radon is the second-leading cause of lung cancer in the United States after smoking and the leading cause among non-smokers.
None of this is detectable by smell, taste, or feel. Radon is a colorless, odorless, naturally occurring radioactive gas that seeps from the soil into building interiors through foundation contact points. The only way to know whether a home has elevated radon is to measure it.
Step 1: choose a test type
Short-term test kits run two to seven days and use either charcoal-canister or alpha-track technology. Kit cost runs fifteen to thirty-five dollars including lab analysis. Long-term tests run three months to a year using alpha-track detectors and produce more reliable average exposure data because they capture seasonal variation. Continuous Radon Monitors (CRMs) are professional-grade electronic instruments used in real-estate transactions and post-mitigation verification.
For a homeowner’s first test, a short-term kit is the right choice. It is fast, cheap, and produces actionable data within two weeks total (kit run plus lab turnaround). Long-term tests are valuable as follow-ups after a short-term test reads borderline.
Step 2: prepare the home for testing
EPA testing protocols are split into Protocol A (closed-house conditions) and Protocol B (typical living conditions). Most short-term tests follow Protocol A: keep windows and exterior doors closed except for normal entry and exit during the test period. Begin closed-house conditions at least twelve hours before starting the test.
Run HVAC normally. Do not change furnace settings, fan-only operation, or any other system specifically for the test. The goal is to measure radon under realistic occupied conditions while preventing high natural ventilation from artificially diluting the reading.
Avoid testing during storms or unusual weather events when air pressure swings change radon entry rates. A stable weather period of two to four days produces the most representative reading.
Step 3: choose the placement location
Test in the lowest occupied level of the home. For Front Range homes with finished basements, that means the basement. For slab-on-grade homes without a basement, the main floor. The detector should sit at breathing height — two to six feet off the floor — in a location away from drafts, direct sunlight, exterior walls, sources of high humidity, or heat-generating appliances.
Avoid placing the kit:
– Directly on the floor (entry-point air can read artificially high)
– Within three feet of windows, doors, or other openings to outside
– Near sump pumps, dryer vents, kitchens, or bathrooms (humidity and ventilation distort readings)
– In closets, crawlspaces, or unfinished utility areas not used for living
A bedroom, living room, or finished basement family room is appropriate. The detector needs forty inches of clearance on all sides for best airflow.
Step 4: run the test for the full duration
Short-term charcoal canister kits typically run two to four days. Alpha-track short-term kits run from a few days up to ninety days. Follow the kit instructions exactly. Starting and stopping early invalidates the test.
Record the start time and date when opening the detector. The kit instructions specify how to seal it at the end and the deadline for mailing to the lab. Charcoal canisters in particular need to be sealed and shipped quickly because the charcoal continues to absorb radon and outgas it after the formal test ends.
Step 5: send the kit to the lab
Most consumer kits include prepaid return shipping. Seal the detector per the instructions, fill out the data sheet (start date and time, stop date and time, address, your contact info), and drop it in the mail same-day or next-day after the test ends. The lab needs the start-to-stop interval to calculate average concentration accurately.
Lab turnaround is typically three to seven business days. Results arrive by email or postal mail depending on the kit provider.
Step 6: read the result and decide
The lab reports radon concentration in picocuries per liter (pCi/L). EPA action levels frame the response:
Above 4.0 pCi/L: mitigation strongly recommended. The EPA action level. Most Front Range mitigation contractors can reduce levels below 4.0 with a sub-slab depressurization system costing roughly twelve to twenty-five hundred dollars in the Denver metro market.
2.0 to 4.0 pCi/L: mitigation should be considered. The EPA notes that any radon exposure carries some risk and a level at this range still produces measurable long-term lung cancer risk. Some homeowners mitigate at this level; others retest to verify the reading is stable.
Below 2.0 pCi/L: mitigation not generally recommended. Retest every two years or after major foundation work, basement finishing, or significant HVAC changes.
Step 7: verify with a follow-up test if needed
A single short-term test is informative but not definitive. EPA recommends either a follow-up short-term test or a long-term test to confirm a borderline reading before committing to mitigation. Two short-term tests run back-to-back can be averaged for a more reliable initial number. A long-term test (90 days or more) captures seasonal variation that short-term tests miss.
For homes purchased in the past year, retest after one full heating season and one full cooling season. Radon levels often change between seasons because closed-house conditions in winter concentrate gas that summer ventilation disperses.
What to do at each result level
For a clean below-2.0 result: keep the test report on file, retest in two years. For a 2.0-to-4.0 result: consider a long-term follow-up or a CRM verification before deciding on mitigation. For a 4.0-or-higher result: contact a certified mitigation contractor for a quote. Post-mitigation, retest in 30 to 90 days to verify the system is performing.
The in-batch how to measure radon levels guide walks through unit interpretation and measurement comparison. The how to check for radon in your house guide covers the quick informal check methodology. The parent radon testing in Colorado hub covers the broader Front Range context.
What can go wrong during a test, and how to avoid it
Three categories of error account for most invalid radon tests. The first is closed-house non-compliance: a window left open overnight, an exterior door propped during gardening, a whole-house fan run during a warm afternoon. Any of these dilutes the indoor radon during the test and produces a falsely low reading. The fix is to brief every household member on the closed-house requirement before the test starts and to set a reminder note near each exterior door.
The second is placement error: a detector placed in a closet, near a window, on the floor, or near a heat-generating appliance. The detector’s airflow assumption is forty inches of clearance with breathing-height placement. The fix is to verify placement against the kit instructions before opening the detector.
The third is timing error: starting the test before closed-house conditions have been established, ending the test early, or letting the test run far longer than the kit specification. Charcoal canister tests in particular are sensitive to timing because the charcoal continues absorbing radon after the formal test end. Seal the detector promptly at the specified stop time and mail it the same day or the next morning.
Front Range seasonal patterns to expect
Front Range Colorado homes typically read higher in winter and lower in summer. The reasons are mechanical: winter heating concentrates indoor air through closed-house conditions and stack-effect convection, while summer ventilation through open windows disperses radon. A short-term test run in January often reads higher than the same test in July.
This seasonal pattern means a single short-term winter test gives a conservative (high) reading, and a single short-term summer test gives a permissive (low) reading. Either is informative but neither is the home’s annual average. The most reliable single number is from a long-term test that spans both seasons.
For homeowners running short-term tests, a winter result above 4.0 may or may not push the annual average above 4.0. A summer result below 2.0 may or may not mean the winter is also clean. Two short-term tests — one in heating season, one in cooling season — together give a much more complete picture than either alone.
How to choose a certified measurement professional
For homeowners who decide a DIY kit isn’t enough — real-estate context, borderline first result, or simply wanting a documented certified test — the Colorado measurement professional should hold NRPP (National Radon Proficiency Program) or NRSB (National Radon Safety Board) certification. The certification covers training in instrument calibration, EPA protocol compliance, and report production.
Ask about the test instrument used (Continuous Radon Monitor preferred over charcoal kit for certified work), the calibration schedule (annual calibration is industry standard), and the report format. The certified professional typically delivers a written report with start and stop timestamps, instrument serial number, calibration date, closed-house compliance notes, and the final pCi/L average.
Costs summary
Short-term DIY kit: fifteen to thirty-five dollars including lab analysis. Long-term DIY kit: twenty-five to fifty dollars. Continuous Radon Monitor self-purchase: one hundred fifty to four hundred dollars for a consumer-grade unit; professional units cost more. Certified test by a state-licensed measurement professional: one hundred fifty to three hundred dollars typical Front Range pricing. Mitigation system installation: twelve to twenty-five hundred dollars typical, more for larger or complex foundations.
When a homeowner should hire a professional measurement instead
For real-estate transactions, most lenders, sellers, and buyers want a certified measurement professional’s report rather than a DIY kit result. Colorado requires radon measurement professionals to be certified through the National Radon Proficiency Program (NRPP) or National Radon Safety Board (NRSB). The certified professional’s report carries more weight in negotiation and disclosure contexts.
References
- EPA radon program — A Citizen’s Guide to Radon — U.S. Environmental Protection Agency
- Colorado Department of Public Health and Environment radon program — CDPHE
- CDC radon and health information — Centers for Disease Control and Prevention
Front Range homeowners with a positive short-term test and questions about mitigation can connect with a vetted local radon professional through our contact page.