How to Check for Radon in Your House: A Plain-Language Guide
How to check for radon in your house comes down to four steps: buy a kit, place it correctly, wait the required time, and mail it to the lab. The total cost is usually under thirty-five dollars and the total elapsed time is about two weeks. For Front Range Colorado homeowners — sitting in EPA Zone 1 where elevated radon is the regional baseline — this is the cheapest single test that pays back in long-term health protection. This guide walks the informal check methodology end to end with EPA, CDC, and Colorado Department of Public Health and Environment guidance current as of 2026.
Step 1: buy a short-term radon test kit
Short-term kits are the fastest path to an initial reading. Two technologies dominate: charcoal canister and alpha-track. Both are sold at hardware stores, online retailers, and through state radon programs at subsidized pricing.
Charcoal canister kits use activated carbon to adsorb radon during the test period. The lab measures decay products in the charcoal to back-calculate the average air concentration. Test duration is typically two to four days. The kit must be mailed to the lab quickly after the test ends because charcoal continues to outgas.
Alpha-track detectors use a small piece of plastic film that records alpha particles emitted by radon decay during the test. Track-etch detectors can run from a few days to a few months. They are less time-sensitive on mailing because the tracks are permanent.
For a quick informal check, either technology works. Cost runs fifteen to thirty-five dollars including lab analysis. The CDPHE radon program sometimes offers low-cost or free kits to Colorado residents — check the CDPHE radon page for current availability.
Step 2: place the kit in the lowest occupied level
The detector goes in the lowest level of the home that is used as living space. For Front Range homes with finished basements: place in the basement. For slab-on-grade homes: main floor. For walkout basements used as a family room or bedroom: place in the walkout, not the upstairs.
Detector placement details:
– Height: two to six feet off the floor (breathing zone)
– Distance from exterior walls: at least three feet
– Distance from windows, doors, vents: at least three feet
– Avoid: closets, kitchens, bathrooms, near sump pumps, near appliances generating heat or humidity
– Clearance: forty inches of open space around the detector for airflow
A good placement spot is a shelf in a bedroom or finished basement family room, or a stable surface in the corner of a living area away from drafts.
Step 3: prepare the home for closed-house conditions
Most short-term tests follow EPA Protocol A, which requires closed-house conditions. Begin those conditions at least twelve hours before opening the detector. Closed-house means: windows and exterior doors closed except for normal entry and exit, HVAC operating normally, no whole-house fans running, no window-mounted air conditioners with vents open to outside.
Continue closed-house conditions for the entire test period. Brief entries and exits through doors are fine. Leaving a window open for hours is not.
The closed-house requirement is not arbitrary. Natural ventilation dilutes indoor radon and produces artificially low readings that misrepresent typical occupied conditions. The protocol ensures the reading reflects realistic exposure when the house is being lived in normally during heating and cooling seasons.
Step 4: open the detector and start the test
Follow the kit instructions to open the detector. Charcoal canister kits typically have a foil seal on the top of the can; remove it carefully and place the can flat on the chosen surface. Alpha-track kits typically have a removable cap or sticker on the detector face.
Record the exact start time and date on the data sheet supplied with the kit. The lab needs this to calculate the time-averaged concentration accurately. A test that ran six days instead of three would produce different chemistry inside the detector, and the lab math depends on knowing the actual interval.
Step 5: wait the full test duration
Charcoal canister: two to four days, per kit specification. Short-term alpha track: usually two to seven days. Do not stop the test early. Do not move the detector during the test. Do not change HVAC settings, open windows, or run additional ventilation.
If something disrupts the test — a furnace failure, a window left open overnight, a hurricane-strength weather front — note the disruption on the data sheet. The lab may flag the reading as unreliable, in which case a retest is appropriate.
Step 6: seal and mail the detector
At the end of the test, seal the detector according to kit instructions. For charcoal canisters, this typically means replacing a foil cap and placing the can in the supplied envelope. For alpha-track detectors, capping the detector face and sealing it in the return mailer.
Record the exact stop time and date. Complete the data sheet: property address, your contact info, start time, stop time, placement location description, any unusual conditions during the test. Drop the package in the mail same-day or next-day. Charcoal canisters in particular need fast turnaround because the chemistry continues changing after the test technically ends.
Step 7: read the lab report
The lab analyzes the detector and reports the average radon concentration in picocuries per liter (pCi/L). Results arrive in three to seven business days, by email or postal mail depending on the kit provider.
EPA action framework summarized at the EPA radon page:
Above 4.0 pCi/L: mitigation strongly recommended
2.0 to 4.0 pCi/L: consider mitigation, particularly with children or non-smokers in the home
Below 2.0 pCi/L: no mitigation recommended; retest in two years or after major changes
When a quick informal check is enough
A single short-term test gives a homeowner a starting answer. For most below-2.0 results in homes with no recent major changes, that answer is sufficient — retest in two years and move on. For results in the 2.0-to-4.0 borderline range, a follow-up test is warranted. For results above 4.0, the question is whether to mitigate immediately or run a confirmatory test first.
The in-batch how to test your home for radon guide walks through the full procedure with more methodology detail. The how to measure radon levels guide covers unit interpretation. The parent radon testing in Colorado hub sets the Front Range context.
When the quick check is not enough
For real-estate transactions, lenders and sellers typically require a certified measurement professional’s report rather than a DIY kit. Colorado requires radon measurement professionals to be certified through NRPP or NRSB. Pricing for a certified test runs one hundred fifty to three hundred dollars typical Front Range rates. The certified professional’s report carries more weight in negotiation.
For homes where the short-term result reads borderline (2.0 to 4.0), a long-term (90+ day) test produces more reliable average-exposure data because it captures seasonal variation that a short-term test misses.
What to do at each result level
Above 4.0: contact a Colorado-certified mitigation professional for a quote. Typical Front Range sub-slab depressurization installation costs twelve to twenty-five hundred dollars. Post-installation, retest in thirty to ninety days to verify the system is working.
Two-to-four range: consider a long-term confirmatory test before mitigation, or simply mitigate if the home has young children, non-smokers, or elderly residents at higher relative risk.
Below 2.0: retest in two years, or sooner if major foundation, basement, or HVAC changes occur.
Tracking the result over time
A first below-2.0 result is good news, but it is one snapshot. Levels can change with soil moisture, seasonal weather, foundation movement, basement finishing, HVAC changes, and natural variability. The two-year retest interval recommended by EPA reflects this. A home that tested low in 2024 might not test low in 2026.
For homeowners wanting more frequent awareness without ongoing kit costs, a consumer Continuous Radon Monitor (Airthings, Corentium, or similar) runs continuously and reports through a smartphone app. The CRM doesn’t replace a certified test for real-estate context, but it provides homeowner-grade ongoing data between formal test events.
For homeowners who tested elevated and mitigated, post-mitigation retesting in 30 to 90 days confirms system performance. After that initial confirmation, retest every two years and after any major change to verify the system continues to perform.
The geology behind Front Range radon
The Front Range sits over geology containing meaningful uranium concentrations. Uranium-238 decays through a chain of intermediate isotopes — uranium, thorium, radium — and produces radon-222 as a gaseous daughter product. The radon migrates upward through soil and rock fractures, accumulating beneath any impermeable layer (a building slab is one such layer) and entering through cracks, joints, and penetrations.
The geology varies across the Front Range. Some neighborhoods sit over higher-uranium granite or shale and produce more radon at the soil-to-air interface. Some sit over alluvial fill with lower uranium content. This variation is why two homes a mile apart can produce very different test results, and why every home needs its own test rather than relying on neighborhood reputation.
Realistic expectations after testing
About half of Colorado homes test above 4.0 pCi/L per CDPHE estimates. The other half test below. Some test very high (above 12). Some test very low (below 1.0). The test produces information; the information drives action.
A high reading is not bad news so much as actionable news. Mitigation works, costs are predictable, and post-mitigation homes have the same long-term lung-cancer risk as homes that never tested high. The barrier is testing, not fixing.
Why neighbors’ results don’t predict yours
A common misunderstanding: “My neighbor tested low, so my home is probably fine too.” This is not how radon works at neighborhood scale. Two adjacent homes can have different foundation construction, different slab penetrations, different sump pit configurations, different HVAC operation, and different occupant patterns. Any of these can drive significantly different indoor radon levels even when the underlying soil is identical.
The Colorado Department of Public Health and Environment publishes county-level radon data showing the geographic distribution of test results across the state. The data is useful for understanding regional trends but does not substitute for an individual home test. Each home stands on its own foundation, draws its own ventilation pattern, and produces its own radon reading.
The cost-to-benefit math
The fifteen-to-thirty-five-dollar kit cost is small compared to any health intervention, any real-estate transaction cost, or any mitigation system. The information it produces shapes long-term lung-cancer risk for everyone living in the home. For Colorado Front Range homeowners, this is the highest health-protective return on a tiny dollar amount available in residential maintenance.
References
- EPA A Citizen’s Guide to Radon — U.S. Environmental Protection Agency
- CDPHE radon program for Colorado residents — Colorado Department of Public Health and Environment
- CDC radon and health — Centers for Disease Control and Prevention
Front Range homeowners with a positive radon result can connect with a vetted local mitigation professional through our contact page.