What Is the Radon Test: A Plain-Language Guide
The phrasing “the radon test” implies there is one specific test, but in practice several types of radon measurement exist and each is right for a different context. In real-estate transactions “the radon test” usually means a 48-hour measurement using a continuous radon monitor under EPA Protocol B with chain-of-custody documentation by a certified professional. In homeowner DIY contexts “the radon test” usually means a charcoal canister kit run for 48 hours. This guide explains the test types, when each applies, and why the real-estate protocol differs from the homeowner protocol. This guide summarizes EPA Indoor Air Quality and CDPHE guidance current as of 2026.
Part of our Radon Levels guide — start there for the full picture →
What is the radon test: the short answer
The radon test is a measurement of indoor air radon concentration over a specific time interval, reported in picocuries per liter (pCi/L). Several measurement methods produce this number. In a homeowner DIY context, the typical test is a short-term charcoal canister or electret kit run for 48 hours to 7 days, placed at the lowest occupied level of the home. In a real-estate transaction, the typical test is a 48-hour continuous radon monitor (CRM) measurement performed by a NRPP-certified or state-licensed radon professional following EPA Protocol B.
The result of any properly conducted test is comparable: a single pCi/L number representing average radon concentration over the test period. The differences between methods are in cost, equipment, who performs the test, chain-of-custody, and reliability. The Front Range radon testing guide covers method selection for Colorado homeowners.
Short-term test methods
Short-term tests run from 2 days to 90 days. Three categories of detector are common.
Charcoal canister kits are the cheapest option ($15 to $35). They contain activated carbon that absorbs radon during a 48-hour to 7-day exposure. The canister is sealed at the end of the exposure and mailed to a lab that measures radon decay products on the carbon to back-calculate the radon concentration during the exposure period. Charcoal canisters are sensitive to humidity and temperature, which is why kitchen and bathroom placement is prohibited.
Electret ion chambers ($35 to $75) are passive devices that measure ionization current change over the exposure window. The electret can be read locally using a calibration reader or mailed to a lab. Electrets are more tolerant of variable conditions than charcoal canisters and produce reliable results across 2-day to 90-day exposures.
Continuous radon monitors (CRMs) are electronic devices ($150 to $400 for consumer-grade; thousands for professional-grade) that measure radon concentration continuously and log readings on a clock. CRMs are the standard for real-estate testing because they produce hourly readings that allow verification of closed-house conditions and detection of tampering. Some prosumer CRMs (Airthings, RadonEye, Corentium) provide app-based real-time monitoring for homeowners who want longitudinal data.
Long-term test methods
Long-term tests run 90 days to 365 days and produce a more representative annual-average measurement. The standard long-term detector is the alpha-track device.
Alpha-track detectors ($25 to $55) use a piece of polycarbonate or other track-recording plastic that registers etched marks where alpha particles from radon and radon decay products strike the surface. After exposure, the detector is mailed to a lab that chemically etches the plastic, counts the tracks under microscopy, and calculates the average radon concentration. Alpha-tracks are unaffected by humidity or temperature and produce reliable results for exposures up to one year.
Why long-term matters: short-term tests can be biased by weather and house operating conditions during the test window. A 48-hour test during a winter cold snap with high stack effect typically reads higher than a 48-hour test during a mild fall week. The annual-average exposure that drives long-term health risk is better captured by a 90-day or longer measurement than by any single short-term test. EPA recommends long-term measurement when short-term tests give borderline results between 2.0 and 4.0 pCi/L.
EPA Protocol A vs Protocol B
EPA’s measurement protocols distinguish between informational testing (Protocol A) and real-estate testing (Protocol B). Protocol A is the homeowner’s default: a single short-term test of at least 48 hours at the lowest occupied level under closed-house conditions, with a follow-up confirmatory test if the first result is elevated. The follow-up can be a second short-term test or a long-term test.
Protocol B is the real-estate transaction default. It requires either a single short-term test of at least 48 hours with simultaneous duplicate measurement (two detectors side by side), or two sequential short-term tests with the higher of the two used as the result. Chain-of-custody documentation is required throughout. Closed-house conditions must be maintained continuously. The detector should be tamper-resistant or under chain-of-custody supervision because real-estate testing has financial stakes that make tampering a recognized concern.
In practice, Protocol B testing is performed by a NRPP-certified or state-licensed radon professional using a CRM. The CRM logs hourly readings so closed-house conditions can be verified after the test, and tamper events (door openings, fan operation) can be identified in the time series. For a deeper walkthrough see how do they test for radon professional methods.
What “the radon test” means in a real-estate transaction
In a typical Front Range residential real-estate transaction, the buyer’s inspector or a separately hired radon professional places a CRM at the lowest occupied level of the home for 48 hours during the inspection contingency period. The CRM is delivered the same day as the general home inspection. The radon professional or inspector returns to retrieve the CRM 48 hours later, downloads the data, generates a report, and delivers it to the buyer.
The CRM report includes hourly radon readings throughout the 48-hour exposure, an average pCi/L value over the full exposure period, an indication of whether closed-house conditions appeared maintained (large step-changes in readings can indicate door openings or window operations), and a final disposition (action level exceeded, consider mitigation, or acceptable). Cost: $150 to $250 in most Front Range markets, sometimes bundled with the general home inspection.
What “the radon test” means in DIY homeowner testing
For an owner-occupied home with no transaction pending, “the radon test” usually refers to a $15 to $35 charcoal canister kit purchased at the hardware store or online. The homeowner places the kit per the included instructions, runs it for 48 hours to 7 days under closed-house conditions, seals it, and mails it to the lab named on the kit packaging. The lab analyzes the canister and emails or mails results within 5 to 10 business days.
This is the right test for: an annual or biennial check-up, post-mitigation verification, a new-home buyer who wants to verify the builder’s pre-closing test, or anyone with no transaction-related stakes. For real estate, this test type is less defensible because it has no chain-of-custody and no hourly logging.
What the test result actually represents
A radon test result is the average concentration of radon-222 in the indoor air over the test exposure period. The number is reported in picocuries per liter (pCi/L). One picocurie is 0.037 disintegrations per second, so 4.0 pCi/L means 0.148 alpha-particle disintegrations per second per liter of air sampled. The disintegration generates daughter products (polonium, lead, bismuth isotopes) that lodge in lung tissue when inhaled and create the long-term lung cancer risk that drives EPA’s action recommendations.
The EPA action level is 4.0 pCi/L. The consideration level is 2.0 pCi/L. There is no truly safe level; lower is better. WHO recommends 2.7 pCi/L as a guideline. Radon is the second-leading cause of lung cancer in the United States after smoking, per EPA and the Surgeon General.
Reliability and method comparison
All EPA-recognized methods produce comparable results when used correctly. Charcoal canister and CRM measurements typically agree within 20 percent. Alpha-track and short-term measurements typically agree closely when the alpha-track captures a period that includes the short-term exposure. The main reliability differences are not about the detector chemistry but about the conditions during testing.
Tampering, failed closed-house conditions, and weather extremes are the largest sources of variance between tests. A 48-hour test during a high-wind storm can produce a result that does not represent normal conditions. A 48-hour test with windows propped open invalidates the result entirely. The CRM advantage in real-estate testing is the hourly log that lets the analyst spot when conditions were not maintained. The how to test radon methodology guide covers protocol selection.
Specialty testing scenarios
Workplace radon testing is governed by EPA and state radon programs and often uses long-term alpha-track or continuous monitoring for compliance with state radon-in-schools and radon-in-workplaces programs. Some states (Maine, New Jersey, Pennsylvania, Iowa, others) have school radon testing mandates.
Water radon testing (separate from air radon testing) measures radon dissolved in well water. Radon in water is reported in pCi/L but the action level differs from the air standard. Water radon contributes to both air radon (when water is aerated through showers and faucets) and direct ingestion exposure. Water radon testing uses sealed water samples sent to a state-certified lab.
References
- EPA Citizen’s Guide to Radon — U.S. Environmental Protection Agency
- EPA radon measurement methods — U.S. Environmental Protection Agency
- Colorado radon program — Colorado Department of Public Health and Environment
- CDC radon and health — Centers for Disease Control and Prevention
Frequently asked questions
Is one radon test enough?
For a homeowner first pass, yes. EPA recommends a confirmatory second test for any elevated initial result. For real-estate transactions, a single 48-hour CRM test under Protocol B is the standard.
What is the difference between a homeowner test and a real-estate test?
Homeowner tests use charcoal canister or alpha-track kits with no chain-of-custody. Real-estate tests use a continuous radon monitor under EPA Protocol B with chain-of-custody and hourly logging by a certified professional.
How long does a radon test take?
Short-term tests run 48 hours to 7 days. Long-term alpha-track tests run 90 days to one year. Lab analysis adds 5 to 10 business days for short-term kits.
What if my test result is right around 4.0 pCi/L?
Confirm with a second short-term test or a long-term alpha-track. If the average of two short-term tests is at or above 4.0 pCi/L, EPA recommends mitigation. Between 2.0 and 4.0 pCi/L, mitigation is worth considering especially if the lower level is occupied.
Front Range homeowners or buyers needing a vetted radon professional for transaction testing can get in touch here.
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 — $142.99 |