How to Check for Radon: A Step-by-Step Homeowner Guide
Checking for radon is a straightforward process when broken into discrete steps, but small errors at any step can invalidate the result. This guide walks through the homeowner pathway from kit purchase to final result, with each step explained in plain language. The content summarizes EPA and CDC guidance current as of 2026 and is not a substitute for a certified radon measurement professional for results that will inform real-estate transactions, lender requirements, or pre-mitigation system design. The short version: order a kit, place it correctly under closed-house conditions, mail it on time, and read the lab report.
Step 1: Decide which test type fits the situation
Short-term charcoal kit ($25-$50, 48-hour deployment, 1-2 week total turnaround) is the homeowner default for general screening. Long-term alpha-track detector ($30-$80, 90+ day deployment, 3-12 month turnaround) is best for annual-average accuracy when timing is flexible. Professional CRM testing ($125-$200, 48-hour deployment, same-day report) is the standard for real-estate transactions because of tamper-evident hourly data. Pick the type based on what the result will be used for.
Step 2: Order the kit from a certified source
Buy from a vendor whose lab is AARST-NRPP or NRSB certified. Major US brands like AccuStar, RadonAway, and Radonova all carry NRPP certification on their lab analysis. Check the kit’s expiration date on arrival — charcoal canisters lose accuracy past the deployment-window date printed on the canister. Confirm the kit includes the prepaid return mailer, chain-of-custody form, and deployment instructions before opening.
Step 3: Choose the test location
The lowest livable level of the home — basement if finished and used, first floor in slab-on-grade homes. Pick a room with normal occupancy patterns, not a closet or storage area. The room should have stable HVAC operation during the test period. Avoid rooms with high humidity (laundry, bathroom) or active drafts (open near an exterior door). The exact spot within the room comes in step 4.
Step 4: Place the device per EPA protocol
Height: 20 inches to 6 feet above the floor (table height is ideal). Distance from doors and windows: at least 3 feet. Distance from exterior walls: at least 1 foot. Distance from HVAC supply registers: at least 3 feet. Distance from drafts, fans, and humidifiers: keep clear. The device sits in the open on a stable surface, not in a closet, not behind furniture, not on top of an electronics device that radiates heat. Do not handle the device once placed.
Step 5: Establish closed-house conditions
For 12 hours before the test starts and through the entire test period: keep windows closed, keep exterior doors closed (normal entry and exit is fine), let HVAC operate normally (heating and cooling cycles continue as usual), keep whole-house fans and attic fans off, keep continuous bathroom or kitchen exhaust fans off. Normal short-duration exhaust use (bathroom fan after a shower) is acceptable. Failing closed-house conditions invalidates the result.
Step 6: Log the start date and time
Write the start date and time on the chain-of-custody form provided with the kit. Time accuracy matters — the lab uses the start and end timestamps to calculate deployment duration. A 48-hour test that gets logged as 36 hours produces a different concentration calculation than the actual exposure. Most charcoal kits have a self-adhesive label that prints the start time on the canister itself. Use a clear, legible time format (24-hour clock if possible).
Step 7: Leave undisturbed for the deployment period
Do not move the device. Do not pick it up to inspect it. Do not place objects on or near it. Do not change HVAC settings dramatically (going from normal home temperature to vacation-mode temperature would alter air patterns). Family members can move through the room normally — just don’t touch the device or open windows. For 48-hour charcoal tests, the deployment is essentially set-and-forget for two days.
Step 8: Log the end date and time, seal the canister
At the end of the deployment period, log the end date and time on the chain-of-custody form, then seal the charcoal canister per the included instructions — usually a screw-down lid or a foil seal pressed firmly. Once sealed, the canister is no longer absorbing radon. For alpha-track detectors, sealing is less time-sensitive because tracks are permanent etched marks on the film. For more on how kits work, see our how a radon test kit works guide.
Step 9: Mail same-day in the prepaid mailer
Charcoal canister kits are time-sensitive after deployment because the radon decay products on the charcoal continue to decay during transit. Most lab protocols require lab receipt within 4 to 7 days of deployment end; longer transit triggers a “no usable result” flag. Drop the sealed kit at a postal facility same-day, use the prepaid expedited mailer the kit provided, and confirm the tracking number for your records. Alpha-track detectors are not transit-sensitive and can be mailed at a normal schedule.
Step 10: Wait for the lab result
Charcoal canister lab analysis takes 5 to 10 business days from lab receipt. Most labs email a PDF report to the address provided on the chain-of-custody form. Some labs post results on an online portal accessible by the kit serial number. Alpha-track analysis takes 5 to 10 business days from lab receipt after the long deployment period ends. Total elapsed time from kit purchase to result: 1 to 2 weeks for short-term, 3 to 12 months for long-term.
Step 11: Read the report
The report identifies the kit by serial number, lists deployment start and end dates and times, reports the average concentration in pCi/L with measurement uncertainty (typically ±15 to 20 percent for charcoal), notes any closed-house non-compliance issues flagged by the lab, prints the lab’s certification number, and provides interpretation against the EPA 4 pCi/L action threshold. Read the uncertainty figure, not just the central value, when interpreting borderline results.
Step 12: Decide on next steps
Below 2 pCi/L: leave it alone, retest in 2-5 years or after major renovation. 2 to 4 pCi/L: consider mitigation, especially in homes with smokers or young children; follow up with a long-term alpha-track or second short-term test. 4 pCi/L and above: install mitigation system, typically sub-slab depressurization at $1,200 to $2,500 in Colorado. Above 10 pCi/L: install mitigation without delay. The sub-slab depressurization guide covers what mitigation involves.
What if the test fails or produces no result
Common reasons for a no-result outcome: late mailing of charcoal canister (transit too long), closed-house non-compliance flagged on the chain-of-custody form, device damage or contamination during deployment, missing or unreadable deployment timestamps, kit past its expiration date. The appropriate response is to retest with a fresh kit, not to assume the original result was low. A failed test is not a passing result.
How to retest correctly after a borderline result
If the first test shows 2 to 4 pCi/L, run a confirmation test. Options: a second short-term charcoal kit at the same location (cheap, fast), a long-term alpha-track at the same location (more accurate, takes 90+ days), or a professional CRM test (most accurate single test, costs more). EPA’s recommendation is that two short-term tests below 4 pCi/L average is sufficient to skip mitigation; two short-term tests above 4 pCi/L average triggers mitigation.
Multi-level homes: where to test first
Test the lowest livable level first. If that level is below 2 pCi/L, upper levels are virtually always lower and do not need separate testing. If the lowest level is above 4 pCi/L, testing upper levels is informative but does not change the mitigation decision — sub-slab depressurization addresses the source, and reducing concentrations at the lowest level reduces them throughout. Some homeowners test multiple levels simultaneously to map distribution before mitigation.
When to use a professional instead of DIY
Real-estate transactions: certified CRM testing is the standard. Lender-required tests: certified professional is typically required. Pre-mitigation assessment: certified professional brings the calibration documentation and protocol that the mitigation contractor needs for system design. Post-mitigation verification: certified or DIY both work; certified is required if the result is going on a formal disclosure. For the full Front Range testing framework, see our radon testing hub.
What about consumer continuous monitors
Devices like Airthings Wave, Corentium Home, and similar consumer CRMs are useful for ongoing surveillance after mitigation is installed. They display real-time concentrations on a digital readout and can connect to a smartphone app. They are not certified for EPA-protocol testing and should not substitute for a certified short-term test during a real-estate transaction or pre-mitigation assessment. As surveillance tools, they are excellent and worth the $150-$300 cost for any homeowner who has identified elevated radon and installed mitigation.
When to call a professional
Hire a certified AARST-NRPP or NRSB radon measurement professional for any test that will inform a property transaction, a lender requirement, a mitigation-system design, or a formal disclosure. DIY testing produces valid measurements for homeowner decision-making, but certified testing carries weight in transactional and regulatory contexts that DIY does not. For Front Range homes specifically, the high regional radon prevalence makes initial testing — DIY or certified — a high-priority due-diligence item.
References
- EPA Radon Measurement Protocols — U.S. Environmental Protection Agency
- CDC Radon Testing Guidance — Centers for Disease Control and Prevention
- CDPHE Test Your Home for Radon — Colorado Department of Public Health and Environment
- American Lung Association Radon Page — American Lung Association
Front Range homeowners ready to check their homes for radon can reach out through our contact page for a vetted certified provider.