How Do You Test for Radon in Your House: 2026 Step-by-Step
How do you test for radon in your house? The short version: buy a kit or hire a professional, place the detector on the lowest occupied level under closed-house conditions, run for 48 to 96 hours (or longer for a long-term test), and ship to an accredited lab. This guide breaks down each step in detail. This guide summarizes EPA and CDPHE guidance current as of 2026 and is not a substitute for direct consultation with a certified measurement professional when transaction documentation is needed. The whole sequence from kit purchase to actionable result takes 7 to 10 days for a passive test, faster with a continuous monitor.
Part of our Radon Levels guide — start there for the full picture →
Step 1: Decide DIY or professional
The right choice depends on what the result will be used for.
DIY makes sense for baseline screening, post-renovation retests, and ongoing monitoring. A $25 charcoal canister or $200 consumer CRM produces useful data for an informed homeowner.
Professional testing makes sense for real-estate transactions, post-mitigation verification, and borderline results where decision stakes are high. Certified measurement professionals use NRPP-certified CRMs with chain-of-custody documentation, which carries more weight in negotiations and inspections. The companion radon testing services overview covers professional vetting.
Step 2: Pick your test type
Three options.
Charcoal canister (passive short-term)
$15 to $40 retail including lab analysis. 48-to-96-hour deployment. Best for DIY screening. Available at most hardware stores, online retailers, and through CDPHE outreach programs that sometimes offer discounted or free kits to Colorado residents.
Alpha-track detector (passive long-term)
$25 to $80 including lab analysis. 90-day to 1-year deployment. Best for confirming a borderline short-term result or for understanding annual exposure.
Continuous radon monitor (CRM)
$200 to $1,500 for the device. Logs hourly readings indefinitely. Best for ongoing monitoring and homeowners who want continuous visibility.
For a first-time test, a charcoal canister deployed during heating season usually suffices. The DIY radon test guide compares specific kit brands.
Step 3: Pick your test location
The detector goes on the lowest occupied level of the home, in a room where the family regularly lives. For homes with finished basements, the basement is the test location. For homes with unfinished basements used only for storage, the lowest occupied level is the first floor — bedroom, family room, home office.
Within the chosen room, the detector sits 20 to 70 inches above the floor (counter or table height), at least 12 inches from exterior walls, at least 3 feet from doors and windows, away from drafts and heat sources, away from high-humidity areas like an adjacent bathroom door. Stable surface. Not in a closed cabinet. Not on top of an HVAC vent. The radon test basement placement guide covers location selection in detail.
Step 4: Establish closed-house conditions
Closed-house means windows and exterior doors stay closed for 12 hours before the test starts and throughout the test, except for normal short-duration entry and exit. HVAC operates normally — no special settings. Whole-house fans and attic fans off. Continuous bath exhausts off. Window air conditioners can cycle normally. Ceiling fans can run.
Closed-house conditions are easier to maintain in winter than in summer. A test in January is straightforward. A test in July on a hot day with a homeowner who normally keeps windows open requires deliberate effort. Front Range homeowners can typically maintain closed-house conditions from October through April without lifestyle disruption. The when to test for radon companion covers seasonal effects.
Step 5: Deploy the detector
Open the kit. Most charcoal canisters arrive sealed inside a foil pouch. Open the pouch only when ready to deploy — the canister starts absorbing radon decay products immediately. Note the start date and time on the chain-of-custody form included with the kit. Place the canister at the selected test location with the active surface facing up. Do not move the kit during the test. Do not place anything on top of it.
Electret ion chambers work similarly — note the start time and place the device with vents unobstructed. CRMs activate through their on-screen interface. Most CRMs include a 1-hour stabilization period during which the first hour of data is discarded for averaging purposes.
Step 6: Maintain the test
For 48 to 96 hours, leave the kit alone. Maintain closed-house conditions. Track any anomalies — power outages, contractors in the home, extended door-open events for moving furniture, unusually long hot showers without bath exhaust. Note them on the chain-of-custody form. The lab interprets results in context.
Family members should maintain normal occupancy and HVAC patterns. Don’t run unusual ventilation. Don’t leave windows cracked overnight. Set phone reminders if needed. A test invalidated by ventilation changes wastes the time and the $25 kit.
Step 7: Close out and ship
At the end of the test period, reseal the canister in its foil pouch immediately. Note the end date and time on the chain-of-custody form. Complete remaining form fields: home address, exact test location within the home, anomalies, contact email or phone for result delivery.
Ship to the lab the same day or next day. Most kits include prepaid overnight shipping. Charcoal canisters lose accuracy if delivery takes more than 5 days from test end because the half-life of radon decay products limits the measurement window. Same-day shipping is the safest path. Most U.S. post offices, FedEx drop-off boxes, and UPS stores handle the prepaid labels.
Step 8: Wait for results
Lab analysis takes 3 to 7 business days. Most labs email results within 2 business days of receiving the sample. The report includes the address, deployment dates, average radon concentration in pCi/L, lab certification, and basic interpretation.
CRM tests skip the lab step. Results appear on the device or in the manufacturer’s app immediately after the test period ends.
Step 9: Interpret the result
Three result categories.
Under 2 pCi/L: low. Retest every 2 years per EPA recommendation. No immediate action needed.
2 to 4 pCi/L: borderline. EPA suggests considering mitigation. Retest in heating season if the current test was a summer test. A long-term alpha-track detector or CRM clarifies whether winter readings push above action level.
Above 4 pCi/L: elevated. EPA action level. Mitigation strongly recommended. The companion Colorado radon mitigation guide covers what installation looks like and how to read contractor bids.
Step 10: Document and schedule next steps
Save the result in home records. Future buyers, insurers, and contractors will reference the documentation. For low results, calendar a 2-year reminder. For borderline results, schedule a heating-season retest or order a long-term detector. For elevated results, request 2 to 3 mitigation bids within 30 days.
The main radon testing pillar covers ongoing testing strategy for Front Range homeowners and CDPHE outreach resources.
What separates a good test from a wasted test
Five things to get right.
Right location. Lowest occupied level, breathing-space height, away from drafts and heat sources.
Right conditions. Closed-house for 12 hours before and throughout. HVAC normal. No whole-house fans.
Right duration. Minimum 48 hours. 72 to 96 hours improves precision.
Right shipping. Mail same-day or next-day. Don’t let the kit sit in a car for 3 days.
Right documentation. Chain-of-custody form completed accurately. Anomalies logged. Lab can interpret results in context.
When to call a professional instead
Three situations warrant professional measurement rather than DIY.
Real-estate transactions. Buyer’s agents and lenders prefer NRPP-certified professionals with CRM testing and chain-of-custody. DIY tests are technically valid in most states but carry less weight in negotiations.
Post-mitigation verification. After a $1,200-to-$2,500 mitigation install, the verification should be professional-grade. EPA recommends it. Most mitigation contractors include verification testing in their bids.
Repeated borderline results. A DIY pattern of 3.4, 3.7, 3.5 pCi/L over multiple tests doesn’t settle the mitigation question. A professional CRM deployment with tight calibration resolves whether the true average is above or below action level.
Front Range testing context
The entire Colorado Front Range falls in EPA Zone 1. CDPHE estimates roughly 50 percent of Colorado homes test above 4 pCi/L. The prior probability that any given Front Range home requires mitigation is essentially a coin flip. Testing is not optional in any meaningful sense — it just determines which half of the distribution your home belongs to. The Colorado radon overview covers state-specific patterns.
References
- EPA Citizen’s Guide to Radon — U.S. Environmental Protection Agency
- CDPHE Radon Program — Colorado Department of Public Health and Environment
- CDC Radon Health Information — Centers for Disease Control and Prevention
- American Lung Association Radon Overview — American Lung Association
Frequently asked questions
How do I test radon in my house?
Buy a kit from a hardware store or online retailer ($20 to $50 for a passive short-term kit including lab analysis). Place it on the lowest occupied level, 20-to-70 inches above floor, away from drafts and heat. Maintain closed-house conditions for 12 hours before and throughout the 48-to-96-hour deployment. Ship to the lab the same day the test ends.
How long does it take to test radon at home?
Passive kits run 48 to 96 hours of deployment plus 3 to 7 business days for lab analysis — total 7 to 10 days from kit purchase to result. CRM tests produce immediate results after 48 hours of logging. Long-term alpha-track detectors run 90 days to a year for the most representative annual exposure picture.
Where in the house should I put the test?
On the lowest occupied level, in a room where the family regularly lives — basement bedroom, family room, home office. Detector at 20-to-70 inches above floor, away from exterior walls, doors, windows, drafts, heat sources, and high-humidity areas. Avoid storage closets and unoccupied utility rooms.
Can I test radon myself or do I need a professional?
DIY works for baseline screening and ongoing monitoring. Professional measurement is recommended for real-estate transactions, post-mitigation verification, and borderline results where decision stakes are high. NRPP-certified professionals use calibrated CRMs with chain-of-custody documentation that carries weight in negotiations.
Front Range homeowners ready to test can reach out for a vetted measurement professional across the nine-county service area, or use the DIY guide above for a baseline screening test.
Test your home for radon
Radon is invisible and odorless, so a test is the only way to know your level. A short-term kit gives a first reading in days; a digital monitor tracks it over time.
| Product | Why | Buy |
|---|---|---|
 AirChek Charcoal Radon Test Kit | Lab fee usually included; EPA short-term protocol. | Amazon — $21.95 |
 First Alert RD1 Radon Test Kit | Widely stocked; 48-hour charcoal test. | Amazon — $16.98 |
 Airthings Corentium Home | Digital monitor with a long-term average. | Amazon — $143.65 |