How to Do Radon Testing: A Plain-Language Guide
Radon enters Colorado homes through the slab faster than almost anywhere in the country — the EPA’s highest-risk Zone 1 covers nearly the entire state. CDPHE reports about half of tested homes read above 4 pCi/L, so a documented test is the only way to know whether yours is one of them. This guide walks step by step through how to do radon testing using a DIY short-term kit, from buying the canister to reading the lab report. The summary reflects EPA and CDPHE guidance current as of 2026 — consult a licensed mitigation professional for an elevated result and your physician for any health symptoms.
How to Do Radon Testing in Six Steps
The full short-term test procedure is: (1) buy a kit, (2) start closed-house conditions 12 hours before deployment, (3) place the canister in the lowest livable room following EPA placement rules, (4) leave it undisturbed for 48 to 72 hours, (5) seal and mail the kit to the lab on the day the test ends, (6) read the result in pCi/L and compare to the 4 pCi/L action level. Total elapsed time from purchase to result is typically 7 to 12 days. The procedure looks simple but several easy mistakes can invalidate the reading.
Step 1: Buy a Test Kit
Short-term charcoal canister kits are stocked at Front Range hardware retailers — Home Depot, Lowe’s, McGuckin in Boulder — and through CDPHE-discounted sources. Most cost $15 to $30 with lab analysis included. Check the manufacturer’s expiration date on the foil pouch before purchase. Charcoal detection media degrade on the shelf; an expired kit reads artificially low. Air Chek and AccuStar are the most common Colorado-distributed brands.
For long-term testing, alpha-track kits run $25 to $50 and produce a 90-day to 365-day average. The procedure is similar but the time horizon is much longer. The pillar guide on radon testing for Colorado homeowners covers when long-term testing is the better fit.
Step 2: Start Closed-House Conditions
Twelve hours before opening the kit, close all windows and exterior doors except for normal entry and exit. Turn off whole-house fans and window fans. Continue running central HVAC normally because heating and cooling are part of the home’s standard operating pattern. The EPA’s closed-house requirement isolates indoor air from outdoor dilution and produces a worst-case scenario against which the 4 pCi/L threshold was set.
If the test period falls in a Front Range chinook event with predicted gale-force winds, postpone deployment by a day or two. Severe weather changes building pressure differentials and biases the result.
Step 3: Place the Canister
Placement is where most DIY tests fail. The canister belongs in the lowest livable level of the home — a finished basement or main floor on a slab-on-grade build. The room must be used at least eight hours a week. Bathrooms, kitchens, laundry rooms, and closets are disqualified because humidity and airflow distort readings.
Set the canister on a stable horizontal surface. Position 20 inches above the floor, 12 inches from any exterior wall, four inches from other objects, and out of direct sunlight or drafts. Keep it away from fireplaces, HVAC supply registers, and forced-air returns. Record the exact location on the chain-of-custody form. The in-batch radon basement test guide explains why basement placement carries special considerations.
Step 4: Leave It Undisturbed
Most short-term charcoal kits specify 48 hours of exposure; some allow 72 or 96 hours. Follow the manufacturer’s window exactly. Pets and children should be kept from disturbing the canister. Do not move it between rooms. Continue closed-house conditions throughout.
Note the deployment date and time precisely. Sleep schedules and work commutes do not affect the test, but the chain-of-custody window does. Mark a reminder on your phone for the planned end time.
Step 5: Close, Seal, and Mail Same Day
At the exact end of the test window, close the canister per the manufacturer’s instructions. Seal the canister inside the prepaid lab envelope. Complete the chain-of-custody form: deployment date and time, end date and time, address, room, test type. Drop the package at the post office the same day or arrange a postal pickup.
Radon-222 has a 3.8-day half-life, which means the signal absorbed in the charcoal decays continuously during shipping. A kit that sits on a kitchen counter for three days before mailing reads roughly 60 percent of its true value at the lab. Same-day overnight shipping is the operating norm — the prepaid label from most kit makers covers this.
Step 6: Read the Lab Result
Most labs return a single number in picocuries per liter, typically within 5 to 10 business days. The EPA’s action level is 4 pCi/L: mitigation strongly recommended. The 2 to 4 pCi/L range warrants consideration, particularly in Colorado where bedrock uranium content elevates baseline. Below 2 pCi/L the home is in the lower-risk band, though the EPA notes no level of indoor radon is risk-free.
An initial elevated short-term result calls for a confirmatory second test before mitigation. Two short-term tests averaging above 4 pCi/L, or one long-term test above 4 pCi/L, is the EPA’s threshold for action. The in-batch accurate radon testing guide details confirmation logic.
Common DIY Errors
Several mistakes invalidate DIY tests. Placing the kit in a bathroom or laundry room — humidity skews charcoal absorption. Opening windows during the test — dilutes radon and reads artificially low. Running a whole-house fan — same dilution problem. Setting the canister near a fireplace or HVAC vent — drafts and temperature swings affect the chemistry. Letting the kit expire before deployment — degraded charcoal under-reads.
Another frequent error is testing the wrong floor. A reading from an upstairs bedroom is not useful if the family lives mostly in a basement-level walkout. Test where the occupants actually spend time. The in-batch how to test radon in home companion guide covers this in detail.
When DIY Is Not Enough
DIY testing is fine for personal screening and post-mitigation curiosity checks. Real-estate transactions in Colorado require a licensed measurement specialist with a continuous radon monitor running under EPA Protocols for Real Estate Transactions. Lenders and buyers’ agents will not accept DIY chain-of-custody. Post-mitigation compliance testing should also be a pro test. CDPHE maintains a public list of certified mitigators and measurement specialists.
After an Elevated Result
A confirmed reading at or above 4 pCi/L prompts a call to a licensed mitigator. The standard Colorado fix is active sub-slab depressurization: a 4-inch PVC pipe drawn through the slab, an inline fan in the attic or garage, and a vent terminating above the roofline. Front Range installs typically cost $1,200 to $2,500. A post-mitigation test confirms the system brought the home below 4 pCi/L. Many mitigators provide an immediate post-install short-term test as part of the package.
What to Tell the Lab on the Chain-of-Custody Form
Every short-term DIY kit ships with a chain-of-custody form that the homeowner fills out before mailing. Required fields typically include: homeowner name and address, deployment date and time (to the minute), retrieval date and time, exact room location of placement, height above floor, distance from exterior walls, test type (short-term first test, retest, confirmation), and any closed-house condition breaches. Some labs ask whether HVAC ran normally, whether a sump pit was present and open, and the home’s foundation type (basement, slab, crawlspace).
Honesty on the form matters because the lab uses the data to flag potentially invalid tests. A reading of 8 pCi/L from a 24-hour test deployed in a bathroom is not valid; the lab will note the protocol violation on the report.
Front Range Seasonal Strategy
Colorado winter testing produces higher readings than summer because the stack effect drives more soil-gas inflow. For a single short-term test, January or February yields a conservative worst-case result. For homeowners who want to characterize the full annual range, a summer short-term plus a winter short-term spans the typical variation. Average the two for a rough annual estimate, or run a 90-day alpha-track across the heating season for a more rigorous figure.
Chinook events on the Front Range introduce barometric chaos that can spike or depress short-term readings unpredictably. If a 48-hour deployment overlaps a major wind event, repeat the test the following week to verify.
Multi-Floor Testing Strategy
EPA placement rules call for testing the lowest livable level. Front Range homes with walk-out basements, daylight basements, or split-levels sometimes prompt the question of whether to test multiple floors. The standard practice is to test the lowest occupied level. If the result is elevated, a second test on the next floor up can characterize how radon distributes through the home, which informs fan-sizing decisions for mitigation.
Buyers with a multi-floor target home sometimes commission tests on both basement and main floor during the inspection contingency. This costs $200 to $300 extra but produces useful pre-mitigation reference data.
Comparing DIY Procedure to Pro Procedure
A licensed measurement specialist running a pro CRM follows essentially the same procedure as a careful DIY homeowner — closed-house pre-conditioning, EPA placement, test duration matching protocol, retrieval and documentation. The differences are in the equipment, the documentation, and the credential weight. A pro CRM logs hourly readings and detects tampering. A DIY canister produces a single integrated value with no tamper evidence. The lab and the homeowner together document a chain-of-custody that satisfies non-transaction uses.
For a homeowner doing first-time screening, careful DIY procedure is functionally adequate. The accuracy difference between a properly run DIY test and a pro CRM test of the same duration is small relative to the measurement uncertainty bands of both methods.
References
- EPA Citizen’s Guide to Radon — U.S. Environmental Protection Agency
- Testing Your Home for Radon — Colorado Department of Public Health and Environment
- Radon Testing — Centers for Disease Control and Prevention
- Radon Overview — National Institute of Environmental Health Sciences
Front Range homeowners who want a connection to a qualified local radon professional can reach out through our contact page.