What Is Radon Gas Testing: A Plain-Language Guide
The question of what is radon gas testing has two answers: a technical answer about the measurement method, and a procedural answer about what professional testing actually looks like end to end. This guide focuses on the procedural side, walking through the typical workflow when a homeowner hires a NRPP-certified or NRSB-certified radon measurement professional. Understanding the process helps homeowners know what to expect, what questions to ask, and what documentation to retain. This guide summarizes EPA, NRPP, and CDPHE guidance current as of 2026 — consult a certified radon professional for testing on your property.
What radon gas testing is, at the highest level
Radon gas testing is the measurement of radon-222 concentration in indoor air using a detection method calibrated and validated for the application. Tests can be short-term (2 to 7 days) or long-term (90 days to one year), DIY (consumer kit) or professional (NRPP- or NRSB-certified technician with calibrated equipment), and screening-grade (single measurement) or diagnostic-grade (multiple measurements across rooms, seasons, or pre- and post-mitigation). The professional-grade short-term test under closed-house conditions using a continuous radon monitor is the dominant approach for real estate transactions.
Why hire a professional
Four scenarios justify the professional premium. First: real estate transactions where chain of custody is contested. Second: post-mitigation clearance testing required by a state program or by a buyer in a transaction. Third: timeline constraints where 48-hour results matter more than the 7-to-14-day lab turnaround of DIY tests. Fourth: diagnostic situations where hourly data identifies the source of high readings. Professional testing typically runs $150 to $250 standalone or $125 to $200 bundled with a home inspection. Our radon testing for home inspection guide covers the bundled pathway.
Step 1: scheduling and intake
The professional process starts with scheduling. The technician confirms the test type (short-term CRM, long-term alpha-track, or post-mitigation verification), the property address, the planned test duration, and the access requirements. For a typical real estate test, deployment happens early in the inspection contingency window to allow time for confirmation testing if results are elevated. Intake includes confirmation that the home has been under closed-house conditions for 12 hours before deployment, or instructions for the occupants to establish closed-house conditions.
Step 2: device selection and calibration
The professional brings a calibrated continuous radon monitor (CRM). Common models include Sun Nuclear 1029 and 1030, Femto-Tech CRM, Pylon AB-5, and Spirit. Each device carries calibration documentation traceable to NIST standards. Annual calibration verification is part of the professional’s workflow. The CRM records hourly readings of radon concentration, temperature, humidity, and barometric pressure. Some devices include tilt sensors that detect movement of the device, useful for tamper documentation in transactional contexts.
Step 3: device placement and chain of custody
The technician places the CRM in the lowest livable level of the home following EPA placement rules: 20 to 70 inches above floor, away from drafts, walls, and HVAC vents. Tamper seals or photo documentation establish chain of custody from the moment of placement. Some professionals apply a numbered seal that must be broken to move the device. The CRM is programmed to start logging and to record the start timestamp. Total on-site time for deployment is typically 30 to 60 minutes. See our day-by-day radon test timeline for the full sequence.
Step 4: the exposure window
The CRM runs for 48 to 96 hours, depending on protocol. EPA’s minimum short-term exposure is 48 hours; 96 hours produces a more representative average. Throughout the exposure window, occupants maintain closed-house conditions. The CRM records hourly readings; many professionals can pull preliminary data remotely if the device supports cellular or Wi-Fi connectivity, but most final reporting uses the data downloaded at retrieval. The exposure window is the only period the homeowner is responsible for managing on their own; the professional handles before and after.
Step 5: retrieval and data download
The technician returns at the scheduled end of the exposure window. Tamper seals are inspected and documented. The device is retrieved, and data is downloaded to a laptop or directly to a cloud platform. The download produces a CSV file or proprietary format showing hourly readings of radon concentration, temperature, humidity, and barometric pressure. The data is reviewed for anomalies: sudden drops indicating ventilation events, tamper flags, or device errors. Anomalies are noted for the report. Total on-site retrieval time is 15 to 30 minutes.
Step 6: report generation
The professional generates a written report including: property address, test dates and duration, device model and calibration certificate, hourly readings chart, average and median values, peak and minimum values, temperature and humidity ranges, closed-house conditions confirmation, tamper status, technician name and certification number (NRPP or NRSB), and interpretation against EPA action level. The report is typically delivered within 24 to 48 hours of retrieval. Reports for real estate transactions follow specific state and EPA formatting requirements.
Step 7: interpretation and recommendations
The report interprets the result against EPA’s 4 pCi/L action level. Results above 4 pCi/L trigger a mitigation recommendation. Results between 2 and 4 pCi/L are EPA’s “consider mitigation” zone. Results below 2 pCi/L are below the action threshold but not zero risk. The professional may recommend confirmation testing in a different season, additional rooms, or specific entry-point investigations. For real estate transactions, the report typically does not advise on negotiation strategy; that conversation belongs to the buyer and the buyer’s agent.
Step 8: confirmation testing if results are elevated
For elevated short-term results, EPA recommends confirmation before mitigation. The professional can deploy a second short-term test, a long-term alpha-track for a 90-day average, or both. Some professionals run confirmation in parallel with the first test using two devices simultaneously, satisfying EPA’s two-test protocol in one deployment. Confirmation testing in transactional contexts can add 48 to 96 hours to the timeline; long-term confirmation typically happens post-purchase under the new owner. See our multi-test strategy guide for the layered approach.
NRPP and NRSB certification
The National Radon Proficiency Program (NRPP), administered by the American Association of Radon Scientists and Technologists, certifies measurement and mitigation professionals. The National Radon Safety Board (NRSB) is the second major certifying body. Both require initial training (16 to 40 hours depending on category), proctored exam, and biennial continuing education. Certifications are recognized across state lines; some states layer additional state-specific licensing on top. Homeowners verify certifications through the NRPP or NRSB online directory before hiring.
Pricing breakdown for professional testing
Standalone short-term CRM test: $150 to $250. Bundled with a home inspection: $125 to $200. Long-term alpha-track placement and retrieval: $200 to $350 including the 90-day window. Combined short- and long-term protocol: $400 to $700. Post-mitigation verification testing: $100 to $200 (often included in mitigation contractor’s installation package). Multi-room testing across 2-3 zones: $250 to $450. The Front Range premium runs roughly 10 to 20 percent above national averages due to cost of living.
What the report can and cannot tell you
The report tells you the measured radon concentration during the test window, with confidence bounds, and interprets against EPA’s action level. The report cannot tell you the long-term average without a long-term test, cannot identify the specific entry mechanism without diagnostic testing, and cannot predict whether mitigation will reduce levels to a target threshold (that requires post-mitigation testing). A good professional explains these limits clearly. Reports that overpromise diagnostic detail without the underlying data are a red flag. The parent radon testing in Colorado guide covers the broader decision framework.
Special case: post-mitigation testing
After installation of a sub-slab depressurization system, post-mitigation testing verifies the system reduces radon below the action level. The protocol uses 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. Independent post-mitigation testing by a separate measurement professional eliminates the conflict of interest. Target post-mitigation result is below 2 pCi/L; results between 2 and 4 indicate the system works but room exists for tuning the fan or sealing entry points.
Records and what to retain
Homeowners should retain the radon test report indefinitely. The report becomes part of the seller disclosure on a future sale, supports insurance claims if relevant, and provides the baseline for long-term monitoring. For mitigation systems, retain the installation contract, post-mitigation test report, and annual verification test results. The full radon documentation file typically runs 5 to 15 pages and lives alongside other home records like the original inspection report, appliance manuals, and renovation permits.
Common state-level overlays on the federal protocol
Several states layer additional requirements on top of EPA’s testing protocol. Illinois requires that radon measurement professionals be licensed by the Illinois Emergency Management Agency. New Jersey requires NRPP or NRSB certification for transactional testing. Pennsylvania has its own state certification program. Maine, New York, and Florida each have state-level requirements that supplement the federal framework. Colorado does not currently license radon measurement professionals at the state level, relying on national NRPP and NRSB certifications for credentialing. Homeowners verify the specific state’s requirements before hiring; the professional should know the state-specific rules.
Working with a real estate agent on radon testing
Real estate agents are familiar with the radon testing timeline because it intersects the inspection contingency. Buyers typically schedule the radon test alongside the general home inspection, with results returned before the contingency deadline. If results are elevated, buyers and sellers negotiate either a mitigation requirement (seller installs system before closing), a credit at closing (buyer installs post-purchase), or in some markets a price reduction. Agents experienced in radon-prone regions like the Front Range have standard contract language for each scenario. The radon measurement professional supplies the data; the agent supplies the negotiating framework.
Front Range homeowners researching professional radon testing for an upcoming transaction or post-mitigation verification can reach out through our contact page for a connection to a vetted NRPP-certified professional.
References
- EPA on finding a radon measurement professional — U.S. Environmental Protection Agency
- CDC radon information for homeowners — Centers for Disease Control and Prevention
- CDPHE Colorado radon program — Colorado Department of Public Health and Environment
- NIEHS radon health research — National Institute of Environmental Health Sciences