DIY Radon Test: What Homeowners Need to Know

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A DIY radon test is a fully homeowner-conducted measurement of indoor radon concentration using a consumer-grade kit. The process is straightforward — choose a kit, establish closed-house conditions, place the device correctly, log start and end times, and ship to an accredited lab (or read on-device for electronic monitors) — but each step matters for the result to be valid. This guide is a step-by-step instructional walkthrough following EPA’s standard testing protocol. It summarizes EPA and Colorado Department of Public Health and Environment (CDPHE) guidance current as of 2026 and does not replace direct consultation with a certified radon professional if the result returns above the EPA 4 pCi/L action level.

Why DIY radon testing makes sense

Consumer test kits are accurate when properly used. The lab analysis methods (gamma spectroscopy for charcoal canisters, alpha-track etch counting, electronic monitor counting) match what professional measurement firms use. The variable is the homeowner’s compliance with the testing protocol. Get the protocol right and the DIY result is technically equivalent to a professional measurement; get it wrong and the result is noise.

Radon testing matters especially in Colorado. The state is mostly EPA Zone 1 — the agency’s highest predicted-screening-level category — and roughly half of Colorado homes tested exceed the 4 pCi/L action level. The EPA attributes roughly 21,000 U.S. lung-cancer deaths per year to radon exposure, with the linear no-threshold model meaning even lower levels carry proportional risk.

Step 1: Choose the right kit

Match the kit to the question.

For initial screening

Use a short-term charcoal canister ($15 to $35 including lab analysis). Fast, cheap, and adequate for the question “do I have a radon problem?”

For annual average measurement

Use a long-term alpha-track detector ($25 to $45 including lab analysis). Deployed for 90 days to a full year. Most representative measure of actual exposure.

For ongoing monitoring

Use a continuous radon monitor (CRM) — Airthings, RadonEye, Corentium, or similar consumer electronic models ($150 to $300). Continuous hour-by-hour data, no per-test cost after purchase. Useful for tracking seasonal variation and verifying mitigation system performance.

For real estate transactions

Short-term test (charcoal or CRM) is the standard. Many transactions in Colorado specify that the test must be performed by a CDPHE-certified measurement professional rather than DIY for defensibility — confirm before deploying a DIY test for transaction purposes.

Verify the kit before purchase: AARST-NRPP or NRSB accreditation for the lab (passive kits) or device certification (CRMs). Our companion guide on home radon test kit types covers the buyer-guide comparison in more depth.

Step 2: Set up closed-house conditions

For any short-term test under 96 hours, EPA requires closed-house conditions established at least 12 hours before the test begins. Closed-house conditions mean:

• Windows closed except for normal entry/exit (brief door opens are fine)
• External doors closed except for normal entry/exit
• Window fans, attic fans, and whole-house ventilation systems off or set to minimum
• HVAC running on normal operation (don’t change thermostat settings mid-test)
• No fireplace or wood stove use (these create negative pressure and skew results)
• Normal use only of bathroom fans, range hoods, and dryers (short, intermittent use is fine)

For a 48-hour test, plan on 60 hours of closed-house operation total. The protocol exists because radon levels vary substantially with ventilation; without controlled conditions, results are not interpretable.

Step 3: Choose the placement location

The test belongs in the lowest occupied level of the home.

• If the basement is used as living space (bedroom, family room, finished entertainment area), test in the basement
• If the basement is unfinished and only used for storage/utilities, test on the first floor
• For single-story homes on a slab, test on the main floor
• For crawl-space homes, test on the lowest occupied floor

Within the chosen room:

• At least 20 inches above the floor
• At least 3 feet from exterior walls
• At least 1 foot from interior walls
• Away from windows, exterior doors, fans, vents, and direct sunlight
• Away from heat sources (radiators, fireplaces, heat registers)
• On a stable surface that won’t get bumped during the test period

Avoid placing the test in a bathroom (high humidity), kitchen (cooking moisture and exhaust), closet (limited air exchange), or any high-traffic area with frequent door opening.

Step 4: Deploy the device

For a charcoal canister:

1. Open the canister at the placement location
2. Record the exact start date and time on the chain-of-custody form
3. Leave undisturbed for the specified exposure period (typically 48 to 96 hours; check the kit instructions)
4. At the end of the exposure period, close/seal the canister immediately
5. Record the exact end date and time

For an alpha-track detector:

1. Place the detector at the chosen location
2. Record the start date
3. Leave for the specified exposure period (90 days minimum, up to a year)
4. At the end of the exposure period, package and return per kit instructions
5. Record the end date

For a CRM:

1. Power on the device at the chosen location per the manufacturer’s instructions
2. Allow the initial settling period (usually 24 hours) before considering readings final
3. Review the on-device display or companion app for hourly, daily, and long-term averages
4. No shipping required — the device produces results on-device

Step 5: Maintain conditions during the test

The test period is not the time to:

• Open windows for ventilation
• Run window fans or attic fans
• Use the fireplace or wood stove
• Adjust the thermostat outside normal operation
• Move the test kit
• Host a party (lots of door opening, body heat changes, increased moisture)

Normal occupancy is fine — opening doors briefly to come and go, normal cooking, normal showers. The protocol asks for normal closed-house living, not for nobody to live in the house during the test.

Step 6: End the test and ship the kit

For passive kits (charcoal canister, alpha-track):

1. At the end of the exposure period, seal the device immediately
2. Complete the chain-of-custody form with start time, end time, address, and any required details
3. Place in the prepaid return envelope
4. Ship within 24 hours of test completion (especially critical for charcoal canisters, which have a short shelf life after exposure)

For CRMs, no shipping is required — read the result from the on-device display or companion app.

Step 7: Interpret the result

EPA guidance:

• Below 2 pCi/L: Low. Retest every 2 years.
• 2 to 4 pCi/L: Consider mitigation. Long-term retest before deciding.
• 4 to 10 pCi/L: EPA recommends mitigation. Hire a CDPHE-certified mitigator.
• 10+ pCi/L: Mitigation as soon as practical.

If the result is above 4 pCi/L, run a second short-term test or a long-term test for confirmation before committing to mitigation. A single short-term test reflects a specific time window; confirmation is good practice. For more on what comes after a positive result, our companion guide on Colorado radon mitigation covers the next steps.

Common DIY mistakes

Three errors regularly invalidate DIY results.

Opening windows during the test

The most common protocol violation. Even a few hours of open windows can substantially reduce the measured concentration and produce a falsely low result. Stay closed-house for the entire test period.

Wrong placement

Attics, garages, crawl spaces, bathrooms, and high-airflow utility rooms all produce unrepresentative results. Place in the lowest occupied level, away from walls, drafts, and heat sources.

Delayed shipping

Charcoal canisters continue to absorb (and re-emit) radon after the exposure period ends. The longer the device sits after exposure before reaching the lab, the less accurate the result. Ship within 24 hours.

Colorado-specific considerations

Colorado homeowners testing DIY benefit from a few state-specific points:

• Several county health departments distribute free or low-cost test kits seasonally — check Tri-County, Jefferson, Boulder, El Paso, and Denver health department websites for current availability
• Winter testing typically produces the highest readings; if the goal is the worst-case picture for mitigation decisions, test in winter
• Long-term alpha-track testing is especially useful in Colorado because of significant seasonal variation
• Most of the state — including all Front Range counties (Denver, Douglas, Elbert, Arapahoe, Jefferson, El Paso, Adams, Boulder, Broomfield) — is in EPA Zone 1

The broader radon testing pillar for Front Range homeowners covers the regional picture in more depth.

Tracking results over time

For homeowners committing to long-term radon monitoring, keeping a simple log of results pays off over years. A spreadsheet or note with date, test type (charcoal, alpha-track, CRM), location, average reading, and any notable conditions (heating season, fireplace use, basement finishing project) builds a record that’s useful for comparing readings across seasons, evaluating mitigation system performance over its lifetime, and providing documentation if the home is later sold. CRM users have an advantage here because the device or companion app typically logs continuous data automatically. For passive-kit users, write the result on the back of the lab report and store the reports together in a labeled folder with the home’s important records.

Common questions homeowners ask after the first test

Three questions come up regularly after a homeowner gets their first DIY result. Should I test other floors? For most homes the lowest occupied level is the primary concern, and additional floors can be tested for completeness but rarely change the mitigation decision. Should I test outside? Outdoor radon background is typically 0.4 pCi/L; outdoor testing is generally unnecessary for residential decisions because indoor levels are what affect long-term exposure. Should I retest if my reading was very low? EPA recommends retesting every 2 years for readings below 2 pCi/L because radon levels can change over time due to home modifications, foundation settlement, or changes in the surrounding soil. The retest cycle is shorter (annual) after mitigation system installation to verify continued performance.

When to call a professional

DIY testing is the right entry point for most homeowners. Hire a CDPHE-certified radon measurement professional if you need a defensible test result for a real estate transaction (some contracts require it), if your DIY result was above 4 pCi/L and you want verified confirmation, or if you’re verifying a newly installed mitigation system. For mitigation work itself, always hire a CDPHE-certified mitigation professional — proper system design requires training in air-flow calculations and building science.

References

• A Citizen’s Guide to Radon — U.S. Environmental Protection Agency
• EPA Radon Measurement Method Protocols — U.S. EPA
• Colorado Radon Program — Colorado Department of Public Health and Environment
• CDC Radon Information — Centers for Disease Control and Prevention
• Radon and Lung Health — American Lung Association

Colorado Front Range homeowners with elevated DIY test results can reach out through our contact page for an introduction to a CDPHE-certified mitigation professional in Denver, Boulder, Colorado Springs, or the surrounding counties.