LIFE · BMC FIELD MANUAL
Home Radon Test Guide: Device, Placement, Timing and Next Steps
Radon has no useful smell, color or warning sensation. A defensible result comes from the right test, the right room, controlled conditions and a record someone else can understand.
The useful answer
- Testing is the only way to know a home's radon level; age, foundation type, tightness and a neighbor's result cannot clear the property.
- Use the lowest level that is regularly occupied or could reasonably become occupied, then follow the exact device instructions for location and conditions.
- Short-term tests provide a quicker snapshot; tests lasting more than 90 days better represent a year-round average.
- Preserve device, room, dates, conditions, laboratory and result together so the number has context.
- EPA recommends fixing at 4 pCi/L or higher and considering reduction between 2 and 4 pCi/L; qualified professionals and state programs should guide testing disputes and mitigation.
Start with the fact the house cannot tell you
Radon is an invisible, odorless radioactive gas released naturally from rocks, soil and water. CDC says it can accumulate in any home or building, including new or old construction, drafty or sealed buildings, and homes with or without basements. A visual inspection, air smell, carbon-monoxide alarm or ordinary indoor-air monitor does not establish the radon level.
Long-term exposure can cause lung cancer. CDC identifies radon as the second leading cause of lung-cancer deaths in the United States after cigarette smoke, and smoking combined with radon exposure increases risk. This is why testing is a prevention task rather than a response to symptoms.
Do not use a county map, real-estate listing, previous owner's memory or adjacent home's test as a substitute. Those sources can motivate testing, but the result must come from the building and conditions being evaluated.
Choose the test for the decision
CDC describes two broad lanes. Short-term tests measure for 2 to 90 days and provide quicker results. Long-term tests remain for more than 90 days and better represent the home's year-round average because radon varies by day, season, weather and how the building is operated.
A do-it-yourself kit can be appropriate when the instructions, laboratory and state requirements are clear. EPA points consumers to state radon programs and recognized proficiency programs for qualified measurement and mitigation providers. Hiring a qualified tester is especially important when a transaction, dispute, unusual building, state rule or chain-of-custody question makes independence and documentation important.
Before buying a kit, confirm the device type, test duration, expiration date, included laboratory analysis, shipping deadline, result delivery, quality-control instructions and whether your state requires a listed laboratory or credentialed professional. A cheap device that expires before use or cannot reach the laboratory on time is not a bargain.
Choose the room before opening the package
EPA's citizen guide places a test in the lowest level of the home that is regularly used, such as a frequently used basement; otherwise, use the first floor. Select a room used regularly—such as a living room, playroom, den or bedroom—rather than a kitchen or bathroom. The exact kit and state program instructions control when they are more specific.
Keep the device away from drafts, high heat, high humidity and exterior walls, and place it where it will not be disturbed. EPA's guide specifies at least 20 inches above the floor; CDC's current testing page describes raising the device three feet in the middle of the room. Because official consumer pages express placement differently, do not average those numbers or improvise: follow the exact approved device instructions and state-program protocol for the test you are conducting.
Document why the room was chosen. If a basement is about to become an office, bedroom or playroom, test before the change and again when renovations are complete. If a multifamily unit is involved, follow the building-specific and jurisdictional protocol rather than borrowing single-family instructions.
Control conditions without staging a fake house
For a short-term test, EPA instructs occupants to keep windows and outside doors closed as much as possible during the test. For tests lasting only two or three days, close them at least 12 hours before starting. Heating and air-conditioning fans that recirculate indoor air may run, while equipment that brings outside air into the house can affect conditions; follow the test instructions exactly.
Do not run a very short test during unusually severe storms or periods of unusually high winds, according to EPA's guide. Do not move the detector, cover it, place it on the floor, put it beside a supply register or repeatedly open the room to improve the result. A test should measure ordinary controlled conditions, not a temporary performance created for the device.
Post a simple note so household members, cleaners, contractors and guests know the device must not be touched. Record heating and cooling operation, unusual weather, open-window events, construction, power outages and any accidental disturbance. Do not silently discard a compromised condition when interpreting the result.
Use a result record someone else can audit
Build one line of documentation before deployment: property address; unit; lowest occupied level; room and exact position; device brand, model, serial or kit number; expiration; laboratory; start date and time; planned stop date and time; and who placed it. Add a quick room sketch or photograph that does not reveal unrelated private material.
At retrieval, record the actual stop time, device condition, whether it moved, whether seals or indicators changed, and any departure from instructions. For a mail-in device, follow the packaging and shipping deadline immediately. Keep the tracking information and laboratory result with the placement record.
The result file should preserve the reported number and unit, laboratory or monitor identity, measurement period, method, quality notes and the page that explains limitations. A cropped screenshot of one number is not a complete record. This worksheet is the citation-worthy core of the guide: identity, placement, conditions and result remain attached.
Read the number as a decision point, not a diagnosis
In the United States, results are commonly reported in picocuries per liter of air, or pCi/L. EPA recommends fixing a home at 4 pCi/L or higher and considering reduction when results are between 2 and 4 pCi/L because there is no known safe level of radon exposure. Other countries and jurisdictions may use different units or action levels.
CDC says that after a short-term result above 4 pCi/L, take a second short-term or long-term test. If two short-term tests are used, the average informs the decision; a long-term result better reflects a year-round average. A very high first result warrants prompt qualified guidance rather than waiting casually for a season to change.
A low result does not certify the home forever. Retest when a lower level becomes occupied, after major renovation, after mitigation work and as recommended by the state program or qualified professional. Keep previous results so changes in room use, structure and system operation have a history.
Move from measurement to qualified mitigation
Do not treat opening windows as a permanent radon system. CDC describes increased ventilation as temporary and says lowering high radon levels requires technical knowledge and special skills. Contact the state radon program for qualified or state-certified providers and applicable requirements.
Ask a mitigator to explain the proposed method, diagnostic work, fan and pipe placement, electrical work, discharge location, alarm or indicator, labeling, warranties, permits, expected maintenance, post-mitigation test and how the design avoids other building hazards. Compare written scopes, not only price.
Retest after the system is operating to verify the result, and keep the mitigation documents with the house records. A fan sound, gauge position or paid invoice does not prove the concentration was reduced; the post-work measurement closes that loop.
Use the transaction lane when a sale is involved
Home sales compress time and create incentives, so EPA's buyer-and-seller guidance and the state program should control the protocol. Buyers may want an independent qualified tester, and a previous result may not answer the question if it used a different room, predates renovations, lacks documentation or does not represent the area the buyer plans to occupy.
Do not hide, alter, move or interfere with a device. Preserve disclosures and reports according to applicable law and professional requirements. Real-estate agents, inspectors and appraisers have different roles; none should exceed their scope by diagnosing health risk or certifying a mitigation system without the required qualification.
When time is short, the answer is a recognized transaction protocol—not a casual consumer monitor reading. Confirm the applicable state requirements, credential, device, quality control and chain of custody before the test starts.
Frequently asked questions
Can a carbon-monoxide detector sense radon?
No. Radon testing requires a radon measurement device or service. A carbon-monoxide alarm has a different job.
Where should a radon test be placed?
Use the lowest regularly occupied level and a regularly used room, then follow the exact approved device and state-program placement instructions. Avoid kitchens, bathrooms, drafts, heat, humidity and disturbance unless your protocol says otherwise.
How long does a radon test take?
CDC describes short-term tests as 2–90 days and long-term tests as more than 90 days. The exact approved device instructions set the duration.
What result means the home should be fixed?
EPA recommends fixing at 4 pCi/L or higher and considering reduction between 2 and 4 pCi/L. Follow-up testing and a qualified professional should guide the exact response.
Sources and further reading
Claims checked against these official or professional sources on September 19, 2026.
- CDC — Testing Your Home for RadonCurrent public-health guidance on when to test, short- and long-term devices, placement, results and follow-up.
- CDC — Radon and Your HealthHealth-risk context, the limits of symptoms and visual inspection, and qualified mitigation guidance.
- EPA — A Citizen’s Guide to RadonDetailed consumer protocol covering closed-house conditions, placement, follow-up tests, home sales and mitigation.
- EPA — Find a Radon Test Kit or ProfessionalState programs, test-kit resources and recognized professional credential routes.
- EPA — Radon Action LevelEPA action-level and risk-reduction guidance for U.S. homes.