How to Test Home for Radon: 2026 Homeowner Walkthrough
How to test home for radon is one of the most common questions Front Range homeowners ask in the first year of ownership. This guide summarizes EPA, CDPHE, and Colorado state guidance current as of 2026 and is not a substitute for professional consultation when results approach or exceed action levels. The full process is straightforward: buy or order a test kit, place it correctly, maintain closed-house conditions, return it to the lab or read the device, and decide on action based on the result. Each step has specific protocols that determine whether the result is accurate enough to base mitigation decisions on. This article walks through the entire process.
How to Test Home for Radon: The Full Process
The five steps to test a home for radon are: select the right test type, prepare the home for closed-house conditions, place the device correctly, run the test for the required duration, and interpret the result against EPA action levels. Each step builds on the previous one. Skipping any step or shortcutting the protocols produces results that may not reflect the home’s actual radon level, which leads to either unnecessary mitigation expense or unaddressed exposure.
For first-time testing, EPA recommends starting with a short-term test (charcoal canister or 2-to-7-day CRM) for initial screening. If the result is below 2 pCi/L, retest every two years. If it is between 2 and 4 pCi/L, retest with a long-term alpha-track detector for a more accurate annual estimate. If it is above 4 pCi/L, retest to confirm and then schedule mitigation. The pillar resource on radon testing in Colorado walks through the state-specific context.
Step One: Buy or Order a Test Kit
Test kits are available through three channels. CDPHE’s Colorado Radon Program offers free test kits to eligible residents in Denver, Douglas, Elbert, Arapahoe, Jefferson, El Paso, Adams, Boulder, and Broomfield counties through county health departments. Hardware stores (Home Depot, Lowe’s, Ace) carry charcoal canister and alpha-track kits at $15 to $40. Online retailers (Amazon, manufacturer websites for Air Chek, Accustar, AccuStar) offer the same kits with similar pricing.
For consumer CRMs, retailers include Amazon, Airthings.com, and specialty electronics stores. Devices like the Airthings Corentium Home, Ecosense RadonEye, and Airthings View Radon run $150 to $300. Some Front Range libraries and county health departments loan CRMs free to residents for short-term home use. Verify any kit is NRPP- or NRSB-listed before purchasing; this listing confirms the kit and partnered lab meet EPA quality assurance requirements. The companion guide on testing for radon yourself covers DIY considerations in depth.
Step Two: Prepare for Closed-House Conditions
Closed-house conditions are required throughout the test period and ideally for 12 hours before the test starts. Close all exterior windows and doors except for normal entry and exit. Do not operate whole-house fans, window air conditioners, or other ventilation equipment that creates significant outdoor air exchange. Operate the HVAC in normal heating or cooling mode (not in continuous “fan only” mode that increases air exchange).
For tests longer than 96 hours, closed-house conditioning prior to the test is less critical because the test duration smooths short-term variability. For real-estate transaction tests, EPA Protocols require 12 hours of pre-test closed-house conditioning regardless of test duration. Front Range homeowners testing in winter (typical heating-season conditions) naturally meet closed-house requirements; summer testing requires more discipline to avoid opening windows on mild days.
Step Three: Place the Device Correctly
Place the test device in the lowest livable level of the home. For homes with a finished basement, this is the basement. For homes with an unfinished basement that could be finished as living space, this is still the basement. For homes without a basement (slab-on-grade construction), this is the lowest occupied floor. Position the device 20 inches to 6 feet above the floor on a stable surface.
Maintain 12 inches of clearance from exterior walls, 12 inches from HVAC supply registers and return grills, and 36 inches from exterior doors. Avoid kitchens, bathrooms, laundry rooms, and other high-humidity or high-airflow areas. Avoid direct sunlight and locations near heaters or air conditioners. For walkout basements, place the device on the side opposite the walkout door to minimize airflow effects. The neighboring guide on radon sampling methods covers the technical considerations behind each placement rule.
Step Four: Run the Test
Charcoal canisters run for 2 to 7 days. Open the canister at the start of the test period and place it per the rules above. Note the start time on the chain-of-custody form. Leave it undisturbed for the duration; do not move it, open it further, or cover it. At the end of the test period, seal the canister per the kit instructions, complete the chain-of-custody form with the stop time, and ship within 7 days to the partnered lab.
Alpha-track detectors run for 90 days to one year. Place the detector and note the start date. Leave it in place for the full duration (alpha-track detectors do not need to be opened or activated, they run continuously). At the end of the period, seal the detector and ship it. Consumer CRMs run continuously after activation. After 24 to 48 hours of equilibration, the rolling average becomes meaningful; a 2-to-7-day rolling average matches the accuracy of a short-term passive test, and a 30-day average matches long-term alpha-track accuracy.
Step Five: Interpret the Result and Take Action
EPA’s action level is 4 pCi/L. At or above this level, mitigation is recommended. EPA’s lifetime lung-cancer risk at 4 pCi/L is approximately 7 per 1,000 for never-smokers and 62 per 1,000 for smokers. Between 2 and 4 pCi/L, EPA recommends considering mitigation, especially in homes with smokers, young children, or other vulnerable occupants. Below 2 pCi/L, no immediate action is recommended but periodic retesting (every 2 years) remains good practice.
Confirm any result above 4 pCi/L with a second test before committing to the $1,200 to $2,500 cost of mitigation. The second test can be a long-term alpha-track for the most accurate annual estimate, or a second short-term test in a different season for a side-by-side comparison. Average two short-term results; if the average exceeds 4 pCi/L, schedule mitigation. If results vary widely, perform a third test or consult a certified measurement professional.
What Happens After a Positive Result
Mitigation systems for Front Range homes typically use sub-slab depressurization (SSD): a fan draws soil gas from beneath the slab through a vent pipe that exhausts above the roof line. The system creates negative pressure under the slab, reversing the natural pressure gradient that drives radon into the home. Cost runs $1,200 to $2,500 for typical slab-on-grade or basement-foundation homes; crawlspace homes run $1,800 to $4,000 due to additional membrane sealing.
Schedule the work with an NRPP- or NRSB-certified mitigation contractor. CDPHE maintains a list of certified contractors operating in Colorado. The contractor will visit the home, design the system based on foundation type and slab dimensions, and install it typically in a single day. Post-mitigation testing within 24 hours to 30 days verifies the system reduced radon below 4 pCi/L; most contractors include this test in the project price.
Retesting Schedule After Initial Result
After a low initial result (below 2 pCi/L), retest every 2 years. Radon concentration changes with foundation settling, soil moisture, HVAC modifications, and other factors. After a borderline result (2 to 4 pCi/L), retest with a long-term alpha-track for a more accurate estimate, and consider mitigation if the long-term average exceeds 2 pCi/L. After mitigation, retest within 30 days to verify performance, then annually for the first 2 years, then every 2 years thereafter as part of the system maintenance routine described in the radon mitigation repair guide.
Total Cost and Timeline
Initial DIY testing costs $15 to $40 for a charcoal canister, $25 to $50 for alpha-track, or $150 to $300 for a consumer CRM (one-time cost). Lab turnaround for passive tests runs 5 to 14 business days. CRM results are immediate. Total time from buying a kit to having a confirmed result is 1 to 2 weeks for short-term passive tests and 3 to 5 months for long-term alpha-track tests. Mitigation, if needed, adds $1,200 to $2,500 and a single day of installation work.
How to Make Your First Test Count
The five steps work as a system. Skipping any one introduces bias that can mislead the mitigation decision. Choose an NRPP- or NRSB-listed kit, maintain closed-house conditions, place the device per the rules, run the full duration, and ship promptly for passive tests. Treat the result as a screening, not a final answer; any reading above 4 pCi/L deserves confirmation before paying for mitigation, and any reading below 4 pCi/L deserves retest in 2 years because conditions change.
What Front Range Homeowners Should Know About Local Conditions
Front Range counties sit almost entirely in EPA Radon Zone 1, with predicted average indoor radon levels above 4 pCi/L. CDPHE survey data shows individual home results spanning a wide range, from well below 2 pCi/L in some homes to over 20 pCi/L in others. The variation depends on soil composition, foundation construction, slab integrity, and HVAC operation. Within a single neighborhood, adjacent homes can produce dramatically different results.
This variability means a neighbor’s test result is not a reliable indicator of any specific home’s radon level. Testing is the only way to know what a specific house is producing. CDPHE encourages every Front Range homeowner to test at least once, and to retest every two years thereafter. The combination of high-probability geology, extended heating season, and basement-living-space norms makes Front Range homes more susceptible to elevated radon exposure than homes in many other parts of the country.
Common Testing Mistakes to Avoid
Several common mistakes produce misleading test results. Placing the device on the upper floor of a multi-story home rather than in the lowest livable level underestimates basement exposure where families often spend significant time. Placing the device in a kitchen, bathroom, or laundry room introduces humidity and airflow effects that bias the result. Placing the device directly under an HVAC supply register dilutes the local concentration with conditioned air from elsewhere in the home.
Opening windows or doors during the test period reduces the radon concentration relative to typical occupancy. Moving the device during the test invalidates the result because the device cannot integrate exposure across two different locations. Letting the device sit in a sealed package for weeks before placing reduces charcoal absorption capacity. Shipping a charcoal canister days after exposure ends produces low results because the absorbed radon has substantially decayed during the delay. Each of these mistakes is easy to make and easy to avoid with careful protocol adherence.
How to Interpret a Borderline Result
A single test result between 2 and 4 pCi/L is the most ambiguous outcome. The reading is below EPA’s action level but above the WHO recommendation and the level at which some mitigation contractors recommend action. Three options make sense in this range. First, retest with a long-term alpha-track detector to capture annual average exposure; if the average is above 2 pCi/L, consider mitigation. Second, install a consumer CRM for ongoing monitoring to understand whether the borderline reading is a year-round average or driven by specific conditions. Third, evaluate the household’s specific risk factors (smokers, children, elderly residents) and weigh mitigation against the borderline reading.
EPA’s lifetime lung-cancer risk at 2 pCi/L is approximately 4 in 1,000 for never-smokers and 32 in 1,000 for smokers; at 4 pCi/L, it is 7 in 1,000 and 62 in 1,000 respectively. The risk reduction from mitigation in the 2 to 4 pCi/L range is real but smaller than at higher levels, and the $1,200 to $2,500 cost is the same regardless of starting level. Households with smokers benefit most from mitigation at lower readings because their baseline risk is much higher.
References
- EPA Citizen’s Guide to Radon Testing — U.S. Environmental Protection Agency
- CDPHE Radon Testing Program — Colorado Department of Public Health and Environment
- CDC Radon Home Testing Information — Centers for Disease Control and Prevention
- American Lung Association Radon Testing Guide — American Lung Association
For Front Range homeowners with a recent high reading or planning a pre-purchase radon test, get in touch here for a connection to a certified local radon professional.