How Do They Test for Radon: A Plain-Language Guide
“How do they test for radon” is the phrasing homeowners use when asking about professional testing rather than DIY kits. The professional protocol differs from DIY in several ways: equipment (continuous radon monitor instead of charcoal canister), procedure (chain-of-custody, calibration verification, hourly logging), credentials (NRPP-certified or state-licensed professional), and use case (real-estate transactions, post-mitigation verification, and elevated-result confirmation). This guide explains the professional workflow end to end. This guide summarizes EPA Indoor Air Quality, AARST MAH-2019, and CDPHE guidance current as of 2026.
How do they test for radon: the professional workflow
A certified radon professional arrives at the home with a continuous radon monitor (CRM), a chain-of-custody form, calibration records, and a placement plan. The placement plan considers the home’s foundation type, the lowest occupied level, and the specific room within that level. The professional places the CRM per AARST MAH-2019 (the American Association of Radon Scientists and Technologists protocol for residential measurement), starts the device, records the start time and conditions, and leaves a chain-of-custody seal on the device.
Forty-eight hours later, the professional returns. They verify the seal is intact (any tampering would be evidenced by a broken seal or unusual readings in the hourly log), stop the CRM, download the data, generate a report, and deliver it to the client. The deliverable includes the hourly time series, the average pCi/L over the 48-hour exposure, closed-house condition verification, and a recommended action. The Front Range radon testing guide covers when professional testing is the right call.
Continuous radon monitors vs. DIY kits
A CRM is an electronic device with an internal radon detection chamber (typically a pulsed ion chamber or an electrostatic alpha particle collector), a real-time clock, data logging, and onboard software. Professional CRMs (Femto-Tech, Sun Nuclear, AlphaGuard, Spirit) cost $1,500 to $5,000 and undergo annual calibration against certified radon sources. Consumer-grade CRMs (Airthings, RadonEye, Corentium) cost $150 to $400 and are suitable for homeowner monitoring but not for professional Protocol B real-estate testing.
The advantages of professional CRM measurement over DIY kits: hourly logging that allows verification of closed-house conditions, calibration traceability to certified radon sources, chain-of-custody documentation that makes results defensible in transactions, faster turnaround (results immediately on retrieval rather than waiting for lab analysis), and the option to repeat the test if conditions were not maintained without buying another kit.
What the hourly time series reveals
A CRM hourly log shows radon concentration sampled every hour during the 48-hour exposure. The log reveals patterns invisible to single-number averages: a sudden drop in concentration mid-test that indicates a window or door was opened, a slow drift upward that indicates the home is reaching steady state, diurnal patterns related to HVAC operation, or a sudden spike that indicates the CRM was moved or disturbed. The analyst uses these patterns to determine whether the 48-hour average is representative or biased by an event during the test.
AARST MAH-2019 protocol in plain language
AARST MAH-2019 is the American Association of Radon Scientists and Technologists Measurement of Airborne Health Protocol for residential testing. It is the de facto standard for professional radon measurement in the United States. The protocol specifies: equipment must be NRSB or AARST-NRPP-listed and within calibration; pre-test closed-house conditions for at least 12 hours; placement at the lowest occupied level, 20 inches to 6 feet above the floor, away from windows and exterior walls; minimum test duration of 48 hours; chain-of-custody documentation from placement to retrieval; and post-test report content requirements.
Compliance with AARST MAH-2019 is what differentiates a defensible professional test from a homeowner DIY test. NRPP certification training covers the protocol in detail. State-licensed radon measurement professionals in states with licensing programs (Maine, New Jersey, Illinois, and others) are required to follow AARST MAH-2019 or an equivalent state protocol. The what is the radon test guide covers test type distinctions.
Calibration verification: why it matters
Professional CRMs must be calibrated annually against certified radon sources traceable to NIST (the National Institute of Standards and Technology) or an equivalent national metrology institute. Calibration verification confirms the instrument reads accurately across the range of concentrations typically encountered in homes (0 to 50 pCi/L). Drift over time, mechanical wear, and electronic component aging can cause an uncalibrated instrument to read high or low; calibration catches and corrects this.
A professional carrying a calibrated CRM should be able to produce the most recent calibration certificate on request. Ask. The certificate identifies the instrument serial number, the date of calibration, the calibration laboratory, the certified source used, and the result (within specification or adjustment performed). Calibration certificates expire after one year; any CRM in use beyond its expiration is not protocol-compliant.
Chain-of-custody for real-estate testing
Real-estate radon testing has financial stakes that make tampering a recognized concern. A seller motivated to close the deal might be tempted to open windows during testing to dilute the reading. A buyer’s professional protects against this with chain-of-custody documentation and physical tamper-evident seals.
The chain-of-custody process: the professional records the CRM placement location and conditions on a form, applies a tamper-evident seal to the CRM body, has the homeowner sign acknowledging the placement, and notifies all parties (typically buyer’s agent, listing agent, and seller) that the test is in progress. On retrieval, the professional verifies the seal is intact, reviews the hourly log for unusual events, completes the chain-of-custody form, and notes any anomalies.
If the seal is broken or the hourly log shows clear evidence of tampering (sudden drops to outdoor levels, periods of zero readings during the test window), the test is invalidated and a re-test is required. This protocol is what makes professional testing reliable for transaction decisions in a way DIY kits cannot match.
Test placement decisions in a professional walk-through
The professional’s first task on arrival is the placement decision. They walk through the home, identify the lowest occupied level, note any unusual features (sumps, daylight basements, addition foundations), and choose a placement location that meets all protocol requirements: lowest occupied level, regularly used room, 20 inches to 6 feet above floor, at least 3 feet from exterior walls and openings, away from HVAC vents and combustion appliances.
If the home has multiple foundation types (basement with slab-on-grade addition, for example), the professional may place two CRMs to capture both zones. Real-estate testing standards in some jurisdictions require dual-detector placement (Protocol B simultaneous duplicates) where the result is the higher of the two readings; this protocol catches placement-related variability and protects against single-detector calibration drift.
Cost and turnaround for professional testing
Professional Protocol B radon testing costs $150 to $300 in most Front Range markets. Some general home inspectors bundle radon testing with their inspection at a small premium ($100 to $150 added to the inspection fee). Standalone radon professionals charge slightly more ($175 to $250) but bring deeper specialization and AARST-compliant documentation.
Turnaround: placement takes 30 minutes, the test runs 48 hours, retrieval and report generation takes another 30 to 60 minutes. The full timeline from request to report is typically 60 to 72 hours. Real-estate transactions usually fit this within the inspection contingency period without difficulty.
Post-mitigation verification testing
After installing a radon mitigation system, post-mitigation testing confirms the system reduces concentration to acceptable levels. Best practice for this verification is a 48-hour CRM test under the same Protocol B as initial testing, performed by a certified professional. The target is below 4.0 pCi/L and ideally below 2.0 pCi/L. Mitigation contractors often include one post-mitigation test in their installation package; subsequent verification testing every two years is the homeowner’s responsibility.
Mitigation system performance can drift over time as the inline fan wears (typical fan lifespan is seven to ten years), as gaskets degrade, or as new foundation cracks develop. Biennial verification testing catches these issues before they create extended periods of elevated exposure. For procedural depth see how to do a radon test step-by-step.
Finding a certified radon professional
NRPP (National Radon Proficiency Program) and NRSB (National Radon Safety Board) are the two major certification organizations. Both maintain searchable directories of certified professionals. Colorado does not currently license radon professionals at the state level but recognizes NRPP and NRSB certifications as the industry standard. CDPHE’s radon program webpage links to certified professional directories.
Ask for certification number when hiring. Verify on the certifying organization’s website. Ask for the most recent calibration certificate of the CRM that will be used. Ask whether the test will follow AARST MAH-2019 or an equivalent state protocol. Ask what the deliverable looks like (sample report, hourly log included). These questions distinguish a serious professional from a generalist who happens to own a CRM.
References
- EPA radon measurement methods — U.S. Environmental Protection Agency
- Colorado radon program certified professional directory — Colorado Department of Public Health and Environment
- EPA find a radon measurement professional — U.S. Environmental Protection Agency
- CDC radon health information — Centers for Disease Control and Prevention
Front Range homeowners or buyers needing a NRPP-certified professional radon test can reach out through our contact page for an introduction to a vetted local pro.