What Is a Safe Radon Level for a Home?
No radon level is completely risk-free, but lower is better. The EPA recommends fixing a home at 4 picocuries per liter (pCi/L) or higher and considering mitigation between 2 and 4 pCi/L, especially when anyone smokes or spends significant time in the lowest level.
Understanding Radon Test Results
Radon is a naturally occurring radioactive gas that can enter through cracks, gaps, drains, sump pits, and other openings in a foundation. You cannot see, smell, or taste it, so testing is the only way to know a home’s level.
In the United States, results are usually reported in pCi/L:
- Below 2 pCi/L: Generally considered a relatively low result. No level is entirely safe, but mitigation may be difficult to justify at very low concentrations.
- 2 to less than 4 pCi/L: Consider mitigation. A longer follow-up test can help confirm the home’s average level.
- 4 pCi/L or higher: Take action to reduce the level. This is the EPA’s recommended action threshold.
- Very high results, such as 10 pCi/L or more: Arrange follow-up testing and contractor evaluation promptly rather than delaying for months.
The EPA’s 4 pCi/L threshold is an action level, not a dividing line between “safe” and “dangerous.” Health risk increases with the radon concentration and length of exposure. Smoking combined with radon exposure creates a substantially greater lung cancer risk.
What to Do After Receiving a Radon Result
First, confirm that the test was performed correctly. A short-term test usually runs for at least 48 hours and should be placed in the lowest level that could regularly be occupied, such as a finished basement or ground-floor room.
For a typical short-term test:
- Keep exterior doors and windows closed except for normal entry and exit.
- Begin closed-house conditions at least 12 hours before a two- to four-day test.
- Place the device away from kitchens, bathrooms, drafts, direct sunlight, and high humidity.
- Do not move, cover, or disturb it.
- Avoid testing during unusually severe storms or periods of extreme wind when possible.
If a result is 4 pCi/L or higher, follow the test provider’s instructions for confirmation. Depending on the initial reading and the time available, that may mean a second short-term test or a long-term test lasting more than 90 days. When the initial result is very high, move more quickly toward mitigation.
For results between 2 and 4 pCi/L, a long-term test is especially useful because radon changes with weather, ventilation, and season. It provides a better estimate of year-round exposure.
Radon Testing During a Home Sale
Home buyers should not rely on neighborhood averages, an old test, or a radon-zone map. Levels can differ significantly between neighboring homes, and renovations or changes to heating and ventilation can affect a previous result.
A professional real-estate test typically takes two to seven days. Build enough time into the inspection period for testing, receipt of the report, and negotiations. If the result is elevated, the parties can agree on mitigation before closing, a seller credit, or money held in escrow.
Look for a report that identifies:
- The device and test method
- Exact start and stop times
- Device location
- Average radon concentration
- Any unusual conditions or signs of interference
- The tester’s certification information
A monitor placed beside an open window, in an unfinished crawlspace, or in a rarely occupied corner may not represent normal exposure. Another red flag is a seller who will not confirm that closed-house conditions were maintained.
How Radon Mitigation Works
Most homes are treated with active soil depressurization. A contractor installs a pipe that draws radon-containing air from beneath the slab or foundation and vents it outdoors above the roofline. A continuously operating fan creates the needed suction.
A standard system typically costs about $1,000 to $2,500, although complex foundations, multiple suction points, crawlspace membranes, electrical work, and local labor rates can raise the price. Basic do-it-yourself test kits commonly cost around $15 to $50, while professional testing often ranges from $100 to $300.
Obtain two or three written mitigation estimates when time permits. A qualified proposal should describe the system design, fan location, discharge point, electrical work, warranty, expected noise, and post-installation testing.
Be cautious of contractors who:
- Promise a specific final reading without inspecting the home
- Recommend sealing cracks as the only solution
- Vent radon near a window, door, or occupied outdoor area
- Cannot show current certification or required state licensing
- Do not include a system-pressure indicator
- Skip post-mitigation testing
Find a certified radon professional near you
Timeline After Mitigation
Many standard systems can be installed in one day, while crawlspaces or homes with several foundation types may take longer. Keep the system running continuously unless a contractor is servicing it.
Test again no sooner than 24 hours after the system begins continuous operation and generally within 30 days of installation. Follow the test device’s instructions and maintain closed-house conditions when required.
After that, test at least every two years, as well as after major renovations, foundation work, or changes to the mitigation system. Check the system’s pressure indicator periodically. If its normal reading changes or the fan stops, contact the installer.
Frequently Asked Questions
Is 4 pCi/L a safe radon level?
Not completely. The EPA uses 4 pCi/L as the point at which a home should be fixed, but risk also exists below that level. Consider reducing levels between 2 and 4 pCi/L.
Is 1 pCi/L a good result?
Yes, 1 pCi/L is relatively low for an indoor measurement. It does not mean zero risk, but mitigation is rarely practical at such a low result.
Can opening windows solve a radon problem?
Opening windows may temporarily lower a reading, but it is not a dependable long-term solution. Levels can rise again when windows close, and ventilation varies with weather.
Does a mitigation system require maintenance?
Usually very little, but the fan must remain on. Watch the pressure indicator, listen for fan failure, test periodically, and replace the fan when it eventually wears out.