High Radon Test Result? What to Do Next
Your radon test came back at 4 pCi/L or higher. What the number means, when to retest, how to hire a mitigator and what a system costs, with EPA guidance.
A radon result of 4 picocuries per liter (pCi/L) or more is EPA's action level: the point at which EPA recommends fixing the home. In metric units that is 150 becquerels per cubic meter (EPA). EPA also says to consider fixing between 2 and 4 pCi/L, since any radon exposure carries some risk. For scale, EPA's Consumer's Guide gives about 0.4 pCi/L as the level normally found in outdoor air.
A high number is common and fixable. EPA estimates about 1 in 15 U.S. homes has an elevated level (Citizen's Guide, 2016), and says some reduction systems can cut levels by up to 99 percent. The steps below take you from the lab report to a working system without overpaying.
First, check what kind of test you ran
EPA splits tests into short-term (2 to 90 days) and long-term (more than 90 days), and says every test should run at least 48 hours. A short-term test is faster; a long-term test gives a better picture of the year-round average. EPA's rule for fixing is a long-term result of 4 pCi/L or more, or the average of two short-term tests at that level.
Some reports give the result in working levels (WL) instead. EPA notes that 0.016 WL is usually about equal to 4 pCi/L in a typical home.
| Your situation | What EPA guidance points to |
|---|---|
| One short-term test at 4 pCi/L or higher | Run a second short-term test or a long-term test, then act on the average or the long-term result |
| Long-term test at 4 pCi/L or higher | Fix the home |
| Average of two short-term tests at 4 pCi/L or higher | Fix the home |
| Result between 2 and 4 pCi/L | Consider fixing; levels below 4 still carry some risk |
| Home sale under way | Follow EPA's Home Buyer's and Seller's Guide, which has its own testing guidance |
Source: EPA Consumer's Guide to Radon Reduction (2010) and EPA, How much can a radon mitigation system cost?
What to do, step by step
- Step 1: Keep the lab report. Note the test type, the dates, the room and the result; every bidder will ask for it, and EPA's checklist has the contractor review how the test was done.
- Step 2: Confirm the result if you only have one short-term test, as in the table above. Test in the lowest lived-in level with windows and doors closed.
- Step 3: Find a credentialed mitigator. EPA advises hiring a qualified contractor and checking with your state radon office first. Several states license or certify radon work; Pennsylvania requires DEP certification (25 Pa. Code Chapter 240) and Ohio an Ohio Department of Health license (OAC 3701-69). Where a state does not regulate radon, EPA suggests asking whether the contractor follows ASTM E2121, the standard practice for installing mitigation systems in existing low-rise homes.
- Step 4: Get more than one written estimate. EPA recommends it, along with references and before-and-after results from past jobs.
- Step 5: Read the contract. EPA lists what it should include: total cost with taxes and permit fees, time to complete, permits, insurance, any guarantee to reach a set radon level, warranties, and whether they transfer if you sell.
- Step 6: Retest after installation, within 30 days but no sooner than 24 hours after the fan starts, with a 2- to 7-day test (EPA). An independent test avoids any conflict of interest.
What it will likely cost
HomeGuide's February 2026 survey puts a typical active soil depressurization system at $1,200 to $2,000 installed, with a national average of $1,600. The same survey lists a professional radon test at $125 to $400, a do-it-yourself kit at $10 to $30, and a permit, where one is required, at $25 to $150. EPA's 2010 guide gave $800 to $2,500 for a typical fix, with an average of about $1,200 (2010 dollars), and $50 to $200 a year to run a sub-slab fan. To see how your foundation changes the number, use the radon mitigation cost calculator or read radon mitigation methods compared.
Common mistakes after a high result
- Treating an air purifier or open windows as the fix. EPA says ventilated homes usually return to previous radon levels within about 12 hours of closing up.
- Accepting a sealing-only bid. EPA does not recommend sealing alone, because it has not been shown to lower radon significantly or consistently.
- Skipping the retest. Without a post-mitigation test you cannot tell whether the system met its guarantee. If the retest is still high, see radon still high after mitigation.
- Ignoring a private well. EPA suggests homes on a private well consider testing water as well as air, since radon in water is released when you shower and run taps.
Questions
How fast do I need to act?
EPA's guidance is about long-term exposure, not an emergency. Confirm the result, then schedule the work; the higher the confirmed level, the sooner it makes sense to fix.
Can I sell a house with a high radon result?
Yes. EPA says a seller with a mitigation system should give buyers information on its operation and maintenance; its Home Buyer's and Seller's Guide covers testing during a sale.
Will a system get me to zero?
No. EPA says most homes can be brought to 2 pCi/L or below with current methods; outdoor air itself averages about 0.4 pCi/L.
Check the EPA zone and state test data for your area in radon levels by ZIP code.
Sources
- EPA, Consumer's Guide to Radon Reduction (2010 edition, archived)
- EPA, How much can a radon mitigation system cost?
- EPA, A Citizen's Guide to Radon (2016)
- 25 Pa. Code Chapter 240, radon certification
- Ohio Administrative Code 3701-69-04
- HomeGuide, Radon Mitigation Cost (Feb 5, 2026), cited as text
Prices are published ranges from the sources listed on this page; anything we calculated is labeled as an estimate. Get at least two itemized bids from certified or licensed mitigators. Run the calculator to build your own range.