How Do You Test for Radon in Your Home: A Plain-Language Guide
The question of how do you test for radon in your home gets a step-by-step answer in this guide. The core procedure is straightforward: select a test kit, place it correctly, maintain closed-house conditions, expose for the required duration, seal the device, and ship to the lab. Each step has specific requirements that affect result validity. Skipping or mishandling a step can produce false-negative results that underreport actual radon levels by 30 to 50 percent. This guide summarizes EPA, CDPHE, and NRPP guidance current as of 2026 — consult a certified radon professional for transactional or post-mitigation testing.
Step 1: choose the right kit for your situation
Three kit types fit different situations. Charcoal canisters ($15 to $30 including lab fee) are the fastest option, with 2 to 7 day exposure windows. Alpha-track detectors ($30 to $60) require 90 days to one year of exposure but produce annual averages that better reflect actual yearly dose. Electret ion chambers ($30 to $80) are reusable and accurate but typically used by professionals. For a homeowner running an initial screening test on a normal timeline, the charcoal canister is the standard choice. For long-term verification or post-mitigation monitoring, alpha-track is the EPA-preferred option.
Step 2: verify the lab accreditation
Before deploying the kit, check that the lab listed on the packaging is accredited by either the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB). The accreditation number is typically printed on the kit packaging or in the included paperwork. Accredited labs follow documented quality systems and participate in proficiency testing; non-accredited results may not be accepted for real estate transactions or regulatory submissions. AccuStar, Air Chek, Alpha Energy Labs, and RTCA are well-established accredited providers.
Step 3: choose the right room
Place the test in the lowest livable level of the home. If the basement is finished and used regularly, use the basement. If the basement is unfinished and not used as living space, use the main floor. Avoid bathrooms, kitchens, laundry rooms, and any room with frequent door openings to the exterior. Closets, utility rooms, and crawl spaces are inappropriate. The chosen room should reflect normal occupancy: a room people actually spend time in. See our basement radon test guide for the finished-vs-unfinished placement rules.
Step 4: position the device correctly
Specific placement rules within the chosen room: 20 to 70 inches above the floor (table height is ideal); at least 4 inches from exterior walls; at least 3 feet from windows, doors, fans, and HVAC supply registers; at least 12 inches from interior walls; away from direct sunlight and heat sources; away from areas of high humidity. Placement on a bookshelf, table, or counter at standing height works well. Do not place on the floor; do not place against an exterior wall; do not place near a vent or supply register.
Step 5: set up closed-house conditions
For short-term tests (charcoal canisters, electret ion chambers under 4 days), closed-house conditions must be maintained for 12 hours before the test starts and throughout the exposure window. Closed-house means: all exterior windows and doors closed except for normal entry and exit; HVAC operating in normal mode; fireplace dampers in normal position; bathroom and kitchen exhaust fans used only briefly. Long-term tests (alpha-track over 90 days) do not require closed-house conditions because the exposure window averages over normal occupancy.
Step 6: record the start time
Open the kit only when ready to begin the test. Record the start date and time on the chain-of-custody form supplied with the kit. For charcoal canisters, the start time is when the seal is broken and the canister is placed. For alpha-track detectors, the start time is when the device is removed from its sealed pouch and placed. Some kits have a printed sticker that activates as a humidity indicator; do not handle the sensitive face of the device. Wash hands before handling. See our how a radon test kit works guide for the device chemistry.
Step 7: maintain conditions during exposure
During the exposure window, occupants live normally with the closed-house constraint. Do not block the device, do not move it, do not cover it, and do not touch the sensitive surface. Continue normal HVAC operation. Brief uses of exhaust fans for cooking and showering are acceptable. Severe weather events that require opening windows for safety (smoke, gas leak) invalidate the test; restart with a new kit afterward. Severe weather changes (significant temperature swings, major barometric pressure changes) do not invalidate the test but may shift the result up or down.
Step 8: close out and ship
At the end of the exposure window, seal the device per kit instructions. Charcoal canisters seal with a plastic cap and tape. Alpha-track detectors seal in a return pouch. Complete the chain-of-custody form with end date and time, total exposure hours, room description, address, and contact information. Place the device and form in the supplied return envelope and mail within 24 hours of test completion. Charcoal canisters are time-sensitive: shipping delays of more than 7 days after exposure can affect the lab result because the absorbed radon decays.
Step 9: wait for the lab report
Lab turnaround varies by method. Charcoal canisters: 7 to 14 days from receipt at the lab. Alpha-track: 14 to 30 days. Electret ion chambers: 5 to 10 days. The lab emails or mails a report showing the measured pCi/L value, the lab’s accreditation number, the analyst’s signature, the test method, and the analytical uncertainty. Rush turnaround is available from most labs for $25 to $75 additional fee. The report becomes part of the homeowner’s home records.
Step 10: interpret the result
EPA action level is 4 pCi/L. Results above 4 pCi/L trigger EPA’s recommendation to mitigate. Results between 2 and 4 pCi/L are EPA’s “consider mitigation” zone. Results below 2 pCi/L are below all major action levels. WHO and Norway use a stricter 2.7 pCi/L (100 Bq/m³) threshold; homeowners adopting the more conservative standard mitigate at lower readings. A single short-term result above 4 pCi/L warrants confirmation testing before mitigation; a long-term test result is itself the confirmation.
Multi-room testing for whole-home screening
For homeowners wanting whole-home radon information rather than a single-room snapshot, deploying multiple kits simultaneously in different rooms produces a fuller picture. Typical multi-room placement: basement, main-floor living area, primary bedroom. Three simultaneous kits cost $45 to $90, less than a professional CRM test, and identify which level of the home carries the highest concentration. The mitigation system design depends on the highest measured level and the entry mechanism, so multi-room data informs the contractor’s quote.
Confirmation testing after elevated short-term results
EPA recommends confirmation before mitigation for elevated short-term results. Three confirmation options: a second short-term test in a different season; two simultaneous short-term tests; or a long-term test over 90 days. The confirmation step protects against transient anomalies and seasonal extremes. Most homeowners use a second short-term test for speed; rigorous confirmation uses a long-term alpha-track for the annual average. See our multi-test strategy guide for the layered approach.
Special case: post-mitigation kit testing
After installation of a sub-slab depressurization system, post-mitigation testing verifies the system is reducing radon below the action level. EPA recommends a 24-to-48-hour short-term test starting no earlier than 24 hours after the fan is energized. Many mitigation contractors include the post-test in the installation package using their own CRM, but homeowners can also deploy a $20 charcoal canister for independent verification. Target post-mitigation level is below 2 pCi/L; results between 2 and 4 indicate the system works but room exists for tuning.
Common mistakes that invalidate results
Five common mistakes affect kit results. First: forgetting closed-house conditions for 12 hours before the test starts. Second: placing the device near a window, vent, or exterior door. Third: placing in a bathroom or kitchen where humidity affects charcoal absorption. Fourth: shipping more than 7 days after test completion (charcoal-specific time-decay issue). Fifth: opening the kit early or handling the sensitive face of the device. Avoiding all five takes minutes of attention and produces a defensible result. The parent radon testing in Colorado guide covers the full pathway from test to mitigation.
What to do if the kit is lost or damaged during shipping
Charcoal canisters and alpha-track detectors occasionally arrive at the lab damaged or are lost in transit. Reputable lab providers (AccuStar, Air Chek, Alpha Energy Labs, RTCA) replace lost or damaged kits at no charge if the customer reports the issue within a reasonable window, typically 60 to 90 days from purchase. Tracked shipping with confirmation of delivery reduces the chance of disputes. If the lab cannot analyze the device because of mishandling during exposure (visible humidity damage, broken canister), the lab issues a replacement and requests a fresh deployment under proper conditions.
Testing crawl spaces, attics, and other non-livable zones
EPA testing protocols target livable spaces because exposure occurs where people spend time. Crawl spaces, attics, garages, and unfinished basements that are not used as living areas are typically not the primary test location. However, diagnostic testing in these zones can identify entry mechanisms for the home’s measured radon. A high crawl-space reading combined with a moderate main-floor reading points to crawl-space pressure-driven entry, suggesting crawl-space encapsulation or ventilation as part of the mitigation approach. Diagnostic testing across zones is typically done by a professional, not by deploying multiple consumer kits.
Testing in homes with mitigation systems already installed
Homes purchased with an existing radon mitigation system should be tested to verify the system is still performing. Mitigation fans typically last 5 to 10 years; failure produces gradual rather than sudden return to elevated levels, and homeowners may not notice until a routine test. EPA recommends testing every 2 years on mitigated homes and immediately after any significant renovation that disturbs the foundation. A 48-hour kit test under closed-house conditions confirms the system is reducing levels below the action threshold. Failed systems require fan replacement or system tuning before re-testing.
Front Range homeowners with elevated kit results who want a connection to a vetted mitigation contractor can reach out through our contact page.
References
- EPA Citizen’s Guide to Radon — U.S. Environmental Protection Agency
- CDC radon resources for homeowners — Centers for Disease Control and Prevention
- CDPHE radon program and free test kit availability — Colorado Department of Public Health and Environment
- NIEHS radon health research — National Institute of Environmental Health Sciences