How to test your home for radon gas
Radon is a naturally occurring radioactive gas released as uranium breaks down in soil, rock, and groundwater. Because it has no reliable smell, color, or taste, you cannot identify a problem by inspecting walls, floors, or air vents. Testing is the only practical way to determine whether it is entering your home.
The gas can move through cracks in foundations, construction joints, sump pits, crawl spaces, gaps around pipes, and other openings between the soil and the building. Indoor levels may vary from one property to the next, and even neighboring homes can produce different readings.
A careful test does not require specialized repair skills. Homeowners can use an approved kit, follow the placement and timing instructions, and send the device to a laboratory when required. The result provides a basis for deciding whether additional testing or radon reduction work is needed.
Why radon deserves attention
Long-term exposure to elevated radon levels increases the risk of lung cancer. The risk is especially serious for people who smoke or have smoked, because tobacco smoke and radon exposure can compound one another. Testing is therefore a routine home health precaution rather than a response reserved for visibly damaged properties.
Radon levels often change with weather, soil conditions, pressure differences, ventilation, and the operation of heating or cooling equipment. A result from one season may not represent the level at another time of year. This is why a single screening result should be viewed in context, particularly when it is near the recommended action level.
The U.S. Environmental Protection Agency uses 4 picocuries per liter, written as 4 pCi/L, as the level at which homeowners should take action to reduce radon. There is no known completely risk-free level, so readings between 2 and 4 pCi/L may also justify mitigation discussions and follow-up testing.
Prepare the home before testing
Choose the lowest level of the home that people regularly use, such as a basement family room or ground-floor bedroom. Do not place the detector in a kitchen, bathroom, laundry room, hallway, crawl space, or an area with unusually high humidity unless the kit instructions specifically allow it. If the basement is unfinished and never occupied, test the lowest regularly used living area instead.
Keep exterior doors and windows closed as much as possible during the test. Normal entry and exit are acceptable, but avoid leaving windows open, using fans that bring in outdoor air, or operating whole-house ventilation in an unusual way. These changes can dilute indoor radon and make the reading less representative.
Follow the kit’s closed-house requirements before placing the device. Record the start date, location, weather conditions if requested, and any unusual events such as construction, flooding, or a power failure. If the property has a crawl space, slab, sump, or recent foundation work, note those details for later interpretation.
Select a testing method
Short-term tests usually remain in place from two to 90 days. They provide a quick screening result and are useful when buying, selling, or checking a home for the first time. Charcoal canisters, alpha-track devices, electret ion chambers, and some digital monitors are common options, but their accuracy depends on correct placement and handling.
Long-term tests run for more than 90 days and can provide a better estimate of the home’s average exposure across changing weather and occupancy conditions. Alpha-track detectors are frequently used for this purpose. A long-term test may be particularly useful when a short-term result is close to the action level or when seasonal variation is likely.
Buy a device from a provider using a kit approved by a recognized radon measurement program, such as the National Radon Proficiency Program or the National Radon Safety Board. Some kits require laboratory analysis, while others display a result electronically. Read the expiration date, shipping instructions, and reporting process before opening the package.
| Testing option | Typical duration | Main benefit | Important limitation |
|---|---|---|---|
| Short-term charcoal test | 2–90 days | Fast, affordable screening | Sensitive to unusual weather and ventilation |
| Alpha-track test | More than 90 days | Better long-term average | Results take longer to receive |
| Electret ion chamber | A few days to 90 days | Precise electronic measurement | Requires careful handling and approved processing |
| Digital continuous monitor | Several days or longer | Shows changes over time | Device quality and calibration vary |
Place the detector correctly
Set the detector on a stable surface about 20 inches to six feet above the floor, or at the height specified by the manufacturer. Keep it at least three feet from windows, doors, exterior walls, vents, fireplaces, direct sunlight, and sources of heat or moisture. The device should be in an area where it will not be bumped, covered, or moved.
Place only one detector in a small room unless the instructions call for multiple devices. Do not put it inside a cabinet, on a shelf crowded with belongings, or directly beside a sump pump. A basement room with regular occupancy is generally a useful testing location because it reflects the air people may breathe over time.
If you are testing more than one level, use separate detectors and label each location clearly. Homeowners who are reviewing tree and septic guidance should also remember that outdoor soil disturbances, drainage changes, and foundation conditions can affect general property maintenance, although a tree itself does not provide a reliable indication of indoor radon.
Finish the test and read the result
Leave the device undisturbed for the full period listed in the instructions. When the test ends, seal or package it immediately, complete the information form accurately, and ship it using the recommended method. Delayed shipment, extreme heat, moisture, or an incorrect start and stop time can affect the result.
A reading below 2 pCi/L is generally considered low, but it does not mean the home contains no radon. Between 2 and 4 pCi/L, consider a second test or a long-term test to learn more about the average level. At 4 pCi/L or higher, perform a follow-up test and contact a qualified radon mitigation professional for advice on reducing entry.
If a test result seems unusually high, check that the detector was not placed near a vent, window, furnace, or damp area. Confirm that closed-house conditions were maintained and that the laboratory processed the sample correctly. A repeat test can help distinguish a persistent problem from a testing error or short-lived change.
Habits that support reliable results
Radon testing works best when it becomes part of regular home upkeep rather than a one-time task. Retest after major foundation changes, basement remodeling, drainage work, or the installation of a new heating and ventilation system. Retesting is also sensible when a previous result was elevated or when several years have passed.
Keep a simple record of test dates, locations, results, and mitigation work. This documentation can help identify patterns and may be useful during a future home sale. For related maintenance information, browse these home maintenance articles to keep other parts of the property in good condition.
Use these practices to reduce avoidable testing mistakes:
- Test the lowest regularly occupied level, not merely the most convenient room.
- Maintain closed-house conditions throughout a short-term test.
- Keep the detector away from drafts, heat, moisture, sunlight, and exterior openings.
- Use an approved kit and follow its laboratory shipping instructions precisely.
- Retest after major structural or ventilation changes, or when a result is near 4 pCi/L.
Respond to elevated radon levels
If follow-up testing confirms elevated radon, mitigation commonly involves a soil-suction system that draws radon from beneath the building and vents it safely outdoors. Sealing cracks and openings can support the system, but sealing alone is usually not a dependable solution for high readings. A qualified contractor should evaluate the foundation type, soil conditions, and existing ventilation.
Do not rely on air purifiers, opening windows, or covering a sump pit as permanent fixes. These measures may change a reading temporarily without controlling the source. After a mitigation system is installed, test again to confirm that indoor levels have fallen, then continue periodic testing as recommended.
Order an approved radon test kit, place it carefully, and send it for analysis on schedule. A small amount of time spent measuring indoor air can reveal an invisible problem and help protect the people who live in the home.