To fix high radon, confirm the result with a second test, then hire a licensed radon mitigation professional to install a system that pulls radon from under your home and vents it outside. Sealing cracks or opening windows will not do the job alone. After the work, test again to prove the number came down.
This guide walks through each step in order: what a high reading means, how to confirm it, how the fix works for different foundations, what to expect afterward, and what to do if radon is still high after mitigation.
TL;DR
- At 4 pCi/L or higher, the EPA says to fix the home. At 2 to 4 pCi/L, consider fixing it. Confirm a high short-term result with a second test first.
- The standard fix is a vent pipe and fan that draw radon from beneath the foundation and release it outdoors. Sealing alone is not enough.
- Hire a licensed radon specialist. The CDC warns that contractors who do not specialize in radon reduction can make the problem worse.
- Retest after installation, and again at least every two years. If the number is still high, the answer is diagnosis, not guesswork.
Table of Contents
- What counts as a high radon reading
- Step 1: Confirm the result before you spend money
- Step 2: Choose a qualified professional
- Step 3: Match the system to your foundation
- How long does radon mitigation take?
- What to expect after mitigation
- If radon is still high after mitigation
- Our perspective
- Need a radon system designed for your home?
- Frequently asked questions
- Sources
What counts as a high radon reading
The EPA's action level is 4 picocuries per liter (pCi/L), which is about 150 Bq/m³. The EPA says to fix a home at or above that level and to consider fixing it between 2 and 4 pCi/L. It also notes that no exposure level is known to be safe, so a result under 4 is not a guarantee of zero risk.
The CDC says a result below 2 pCi/L generally needs no immediate action. It adds that you should test again if you start using a lower level of the house, such as a basement bedroom or home office.
Here is how the numbers translate into action:
| Your result | What to do |
|---|---|
| Below 2 pCi/L | Usually no action. Retest after remodeling or if you start living in a lower level. |
| 2 to 4 pCi/L | Consider mitigation. Retest after any work. |
| 4 pCi/L or higher (short-term test) | Run a second test before deciding. |
| Average of two short-term tests, or one long-term test, at 4 or higher | Contact a licensed professional for mitigation. |
Step 1: Confirm the result before you spend money
A single short-term test is a snapshot. Weather, how closed up the house was and where the device sat all move the number. The CDC says a short-term result above 4 pCi/L calls for a second short-term or long-term test. If you take two short-term tests, average them. Mitigation is warranted when that average, or a long-term result, is 4 pCi/L or higher.
Two habits make the second test more trustworthy. First, keep the house in closed-house conditions as the test instructions describe. Second, place the device correctly: our guide on where to put a radon test in the home covers the lowest lived-in level, distance from walls and drafts, and the common mistakes. If you want a professional to run the second test, see our radon testing service. For a deeper look at reading numbers near the line, see why a 4 pCi/L result should be confirmed first.
Can you lower it yourself in the meantime?
Ventilation and sealing can nudge borderline readings down for a short while, but they are not a fix. EPA guidance says sealing foundation cracks and openings is a basic part of most mitigation approaches, yet sealing alone has not been shown to reduce radon significantly or consistently. Treat sealing as a supporting step that helps a system work better.
Step 2: Choose a qualified professional
This is where most of the outcome is decided. The CDC notes that lowering radon takes technical knowledge and that contractors who do not specialize in it could make the problem worse. A general handyman or HVAC crew may not know how to measure pressure under a slab or where to run a suction point.
In Ohio, the state regulates the trade. The Ohio Department of Health's Radon Education and Licensing Program licenses mitigation contractors, mitigation specialists, testers and laboratories. Ask any company for its license number and check it. The EPA also advises contacting your state radon office about state requirements and using the national radon programs to find qualified professionals.
EPA's home buyer's and seller's guide recommends getting estimates from one or more qualified mitigators. When you compare quotes, ask for:
- The license number and proof of the mitigation credential.
- A written scope that names the system type, number of suction points and fan location.
- Where the exhaust pipe will discharge.
- Whether post-installation testing is included and who performs it.
- The total price, with what could change it spelled out before work starts.
If you are in Greater Cincinnati, our radon mitigation cost guide explains what drives the price of a job here.
Step 3: Match the system to your foundation
There is no single design for every house. The EPA says the right system depends on the home's design, including whether it has a basement. The CDC describes the most-used method as a vent pipe and fan that pull radon from beneath the house and vent it outside, and says similar systems can be installed in crawlspace homes.
Here is how that plays out by foundation:
- Basement or slab-on-grade. New York's state radon program calls active subslab suction the most common and usually most reliable method. Pipes draw soil gas from beneath the slab and a fan sends it outdoors.
- Basements with drain tile, a sump pit or hollow block walls. The same program lists drain-tile suction, sump-hole suction and block-wall suction as alternatives or supplements where the foundation suits them. We explain the drain-tile approach in why a running fan is not enough with drain tile.
- Crawlspaces. A vent-and-fan system can work here too, and sealing openings can make it more effective.
Many Greater Cincinnati homes have more than one foundation type: a basement under the main house, a crawlspace under an addition, a slab-on-grade garage. A system designed for one part may not reach the others. That is why site-specific measurement and design matter more than a standard kit. For a plain-language comparison of each design, read how each radon mitigation system works and fits.
How long does radon mitigation take?
For a typical home with a single suction point, installation is often a one-day job. Complex foundations, several suction points, finished basements or difficult pipe routes can stretch that. The contractor should give you a written schedule and a clear picture of what will be cut, drilled or routed through living space before work begins.
The system starts working when the fan runs, but the number to trust comes from testing afterward, not from the date the crew left.
What to expect after mitigation
The EPA says some radon-reduction systems can cut indoor radon by up to 99%, and that even homes with very high levels can be brought below 4 pCi/L with proper systems. Its Consumer's Guide says most homes can be reduced to 2 pCi/L or below with current technology.
To confirm, test again. The EPA recommends an independent, qualified tester. On timing, the only precise rule in our research comes from the ANSI/AARST standard for schools and large buildings, which calls for an initial short-term test no sooner than 24 hours after the system is operating and within 30 days of installation. Residential work is often handled on a similar schedule, but follow your state's requirements and your mitigator's written plan. The CDC recommends retesting a few months after the fix to see whether the reduction held.
A good post-mitigation result is below 4 pCi/L, and the best outcome is under 2. Keep the report. If you sell, buyers and agents will ask for it.
Keeping the result
EPA says owners of active systems should check the warning device or manometer regularly, never turn off the fan, and retest at least every two years. It adds that fans may last five years or more, so plan on an eventual replacement. The CDC likewise suggests retesting every two years and after remodeling. Our radon system maintenance checklist lists what to look at and when. If your fan is noisy, stopped or the gauge has changed, our radon system repair and fan replacement service covers it. Since the fan shares your home with other mechanical equipment, it also helps to think of it alongside home air quality and HVAC upkeep.
If radon is still high after mitigation
A stubborn reading does not mean mitigation failed for good. It means something remains to be found. Start with the simple checks:
- Is the fan running? Look at the manometer or warning device. A fan that was switched off, tripped on a breaker or died will let levels climb back.
- Was the test done correctly? Wrong placement, open windows during a short-term test or a device near a drafty spot can skew a result.
- Has anything changed? Remodeling, a new sump cover, a new opening in the slab or a new HVAC change can alter how air and soil gas move.
If those check out, the work shifts to diagnosis. EPA demonstration research on persistent readings describes further investigation to locate a continuing source after readings stayed above 2.9 pCi/L with an active system. That points to looking for remaining entry pathways rather than assuming the fan is the culprit. We list the common causes and what to check in eight checks for a radon system that is not working.
The fixes a qualified mitigator may recommend include upgrading to a larger fan, adding suction points, or installing a second system, along with sealing newly found openings. Each is a design decision that depends on what pressure measurements under the slab show. Ask the original installer to return first: a reputable contractor will want a high verification result resolved.
Our perspective
Most people who call us after a high test are worried about two things: the health risk and the cost. We think the best response to both is measurement. A house in Greater Cincinnati can have one foundation under the kitchen, another under the addition, and drain tile that connects them in ways nobody drew on a plan. We do not believe in guessing from the street.
That is why we design each system around the specific foundation, give a fixed written quote with no added costs after quoting, and include post-installation verification testing in every mitigation. A radon system is only finished when a test shows it worked, and we want you to have that document in hand, including for a future sale.
Radon is all we do. We hold ANSI/AARST certification for installations, and we would rather explain why a number is high than sell you something you do not need.
— Yoshua
Need a radon system designed for your home?
If your test came back at or above 4 pCi/L, or in the 2 to 4 range and you want it lower, we can measure your home, design a system for its foundation and verify the result afterward. See our radon mitigation services or contact us through our main site for a written quote.
We also work with real estate agents, buyers and sellers who need documented results during a transaction, and with builders who want rough-in systems installed in new construction.
Frequently asked questions
What should I do first if my radon test is high?
Do not panic and do not start sealing. Take a second test, either short-term or long-term. If two short-term results average 4 pCi/L or higher, or a long-term result does, call a licensed radon mitigation professional.
Can I fix high radon by opening windows?
Only briefly, and only for borderline readings. Ventilation does not address the soil gas entering through the foundation. A vent pipe and fan system designed for your foundation is the reliable approach.
What radon level should I expect after mitigation?
The EPA says many homes can be brought to 2 pCi/L or less, and that systems can cut radon by up to 99%. Your own post-installation test is the only number that matters for your house.
How often should I retest after a fix?
Test a few months after the system goes in, then at least every two years, and after any remodeling. Also check the warning device or manometer regularly and never switch the fan off.
Who is allowed to install a radon system in Ohio?
Ohio licenses radon mitigation contractors and specialists through the Ohio Department of Health. Ask for a license number before you sign anything and confirm it with the state.
Sources
- CDC: Testing Your Home for Radon
- CDC: Reducing Radon Levels in Your Home
- EPA: What Is EPA's Action Level for Radon
- EPA: Home Buyer's and Seller's Guide to Radon
- EPA: Radon Hotlines and Information Resources
- EPA: Radon in Homes, Schools and Buildings
- EPA: Consumer's Guide to Radon Reduction
- New York State Department of Health: Radon Mitigation
- ANSI/AARST RMS-LB 2018 with 12/20 Revisions
- EPA: Demonstration of Radon Resistant Construction Techniques
- Ohio Department of Health: Radon Education and Licensing Program