How Do You Do a Radon Test: The Day-by-Day Timeline
How do you do a radon test — the question has a procedural answer that unfolds across roughly seven to ten days from purchase to lab result. This guide walks the chronology day by day, from the moment a homeowner orders a kit through retrieval, mailing, and receipt of results. The framework applies to short-term charcoal canister and electret tests, the two most common consumer formats. Information reflects EPA, CDPHE, and lung.org guidance current as of 2026; consult a state-certified radon professional for real-estate transaction testing or post-mitigation clearance, where DIY kits are not the appropriate format.
Day 0 — purchase and arrival
Order or pick up a short-term charcoal canister test from a hardware store, online retailer, or state-funded program. CDPHE sponsors discounted radon test kits for Colorado residents through county public health offices and partner programs. Kit prices run $15 to $30 for retail and $5 to $15 for state-sponsored kits, with lab analysis typically included in the kit price.
Check the kit contents: a sealed charcoal canister, a placement form, a return envelope or shipping label, and instructions. Verify the canister is sealed (the foil tab on the open face must be intact) and that the kit has not expired. Charcoal canisters have shelf lives — usually six months to one year — and expired kits return inaccurate results.
Day 1 — closed-house preparation
The closed-house protocol begins 12 hours before test placement and continues through retrieval. Required actions:
Close all exterior windows and doors
Normal entry and exit through doors is acceptable but should be minimized. Keep windows closed continuously during the closed-house period.
Operate HVAC normally
The forced-air heating or cooling system should run as it normally does. Whole-house ventilation fans should run as normal. Exhaust fans (bathroom, kitchen) are used briefly but not continuously.
Postpone weather-disturbing activities
If a major storm front is forecast during the test window, consider delaying the test by a day or two. Severe weather can shift radon entry rates dramatically and produce an atypical reading.
Notify household members
Everyone in the household should understand the closed-house protocol so accidental window-opening does not invalidate the test.
Day 1 (afternoon or evening) — place the canister
Open the canister at the chosen test location and record the placement time, date, and conditions on the kit form.
Placement location
Lowest livable level of the home. For most Front Range houses with basements, that means the basement. For ranch homes without basements, the main level. For multi-story homes used by occupants daily on lower floors, place there. Do not place in attics, crawlspaces, or unused storage rooms — the test should reflect actual breathing zones.
Placement height
At least 20 inches above the floor and at least 4 inches from walls. A shelf, table, or sturdy chair works. The canister opening faces upward, with the foil pull-tab removed.
Avoid these locations
Away from exterior walls, drafts, doors, windows, vents, fireplaces, and direct sunlight. Avoid kitchens, bathrooms, and laundry rooms where humidity is high — humidity affects charcoal absorption efficiency. Avoid placement within 3 feet of an exterior wall or 12 inches of a heat source.
Days 2 and 3 — the active test period
Most short-term tests run 48 to 96 hours. The canister sits undisturbed during this time, absorbing radon at a rate proportional to the ambient concentration. Household occupants continue normal activities — sleeping, cooking, entertaining — without opening windows or disturbing the canister.
Monitor weather and HVAC conditions. If a furnace breakdown forces window-opening for safety, the test is compromised and should be restarted. If a household member accidentally moves the canister, mark the time and contact the lab for guidance — minor disturbances are sometimes recoverable, major ones are not.
Day 3 (or 4 or 5) — retrieval and sealing
At the end of the test period, retrieve the canister and immediately seal it according to kit instructions. The seal is critical — once the test ends, the absorbed radon decays at the known rate of radon-222 (3.8-day half-life). The lab corrects for elapsed time between test end and analysis, but delays beyond seven days reduce accuracy.
Record on the kit form: retrieval time and date, total test duration, any unusual conditions during the test, and your contact information. The form ships with the canister to the lab.
Day 3 (same day) — mail to lab
Ship the same day if possible. Use first-class or priority mail; expedited shipping is rarely necessary because the half-life math works out either way, but minimize the delay. The kit’s prepaid envelope or shipping label is usually pre-addressed to the analyzing lab.
If retrieval falls on a Sunday or holiday, mail Monday morning. Avoid leaving the sealed canister in a hot car or at extreme temperatures during transport — both affect absorption-decay calculations.
Days 4 through 7 — lab in transit and analysis
Standard mail typically reaches lab destinations within two to four business days. Once received, the lab begins gamma spectroscopy analysis. Most consumer labs deliver results within seven to ten business days of receipt, sometimes faster.
Day 7 to 10 — result delivery
Most labs email results as a PDF with the measured concentration in picocuries per liter (pCi/L), the test duration, any quality-control notes, and a brief interpretation. Some labs include CDC or EPA action-level reference text.
Reading the result
Below 2.0 pCi/L: routine retest in two years is reasonable. 2.0 to 4.0 pCi/L: consider mitigation, particularly with children or sensitive individuals in the home. 4.0 pCi/L and above: EPA action level. Schedule mitigation. 10 pCi/L and above: prioritize mitigation as quickly as practical.
Day 10 onward — confirmatory testing or mitigation
EPA recommends confirming any short-term test result above 4.0 pCi/L with a follow-up test before committing to mitigation. The confirmatory test can be another short-term canister at a different time of year, a long-term alpha-track detector for 90 days to one year, or a professional continuous radon monitor for 48 hours.
Front Range homeowners with confirmed elevated radon should engage a state-certified radon mitigation contractor. Mitigation systems run $1,200 to $2,500 typical with annual electrical operating costs in the $50 to $150 range. The Colorado radon testing guide covers mitigation in broader context.
Common mistakes that invalidate the test
Five errors recur in DIY radon testing:
Opening windows during the closed-house period
The single most common cause of artificially low readings. Even brief window-opening can drop concentrations measurably.
Wrong location
Placement in a rarely used room, attic, or crawlspace rather than the lowest livable level. Or placement too close to exterior walls, vents, or sunlight.
Delayed mailing
Sitting on the sealed canister for a week before mailing reduces accuracy because the gamma signal from absorbed radon decays in the meantime. Ship within 24 hours of test end.
Improper sealing
Failure to apply the foil seal correctly leaves the canister vulnerable to absorbing additional radon during transport, biasing the reading.
Testing during atypical conditions
Tests during extreme weather events, while the furnace is off, or during a vacation when HVAC is not running represent abnormal conditions. Re-test during normal occupancy.
When DIY is not the right format
Three scenarios call for professional CRM testing instead of DIY:
Real-estate transactions
The data trail from a CRM and the chain of custody through a certified professional carry transactional weight. DIY results, while accurate when used correctly, are easier for an opposing party to challenge.
Post-mitigation clearance
Verifying mitigation system performance benefits from the hour-by-hour data a CRM produces, including diagnostic data about system on/off cycles.
Disputed or suspicious results
Confirmatory testing after an anomalous DIY result is best handled with a different methodology and operator to reduce systematic error.
The how is a radon test done guide walks the procedure from a slightly different angle.
When to call a professional
For real-estate testing, post-mitigation clearance, or any consequential measurement where defensibility matters, hire a state-certified radon measurement professional. Front Range homeowners can verify CDPHE and NRPP certification through state databases. For routine DIY surveillance, a properly executed charcoal canister test gives reliable results when the closed-house protocol and placement rules are followed carefully.
References
- EPA Radon Publications and Test Guidance — U.S. Environmental Protection Agency
- CDPHE Radon Program — Colorado Department of Public Health and Environment
- American Lung Association Radon Resource — Lung.org
- CDC Radon Prevention Information — Centers for Disease Control and Prevention
Front Range homeowners planning a radon test for a purchase or routine surveillance can reach out through our contact page for a connection to a state-certified Colorado radon measurement professional.