Radon in Franklin County, OH: Test Data and Mitigation Cost

Franklin County has more radon test results on file than any other Ohio county. On the Ohio Department of Health radon dashboard (tests since 2010, pulled Oct 16, 2026), Franklin County shows 114,203 pre-mitigation results, with 44.88% at EPA's 4 pCi/L action level or higher.

Across Ohio as a whole, the same ODH file works out to 34.4% when every test is weighted equally, so Franklin sits about ten points higher. ODH reports Franklin County's arithmetic mean at 5.9 pCi/L and its geometric mean at 3.64 pCi/L, and EPA's 1993 radon zone map places the county in Zone 1, the highest predicted potential.

Because Columbus and its suburbs test so heavily, the county figure is unusually stable, but it is still a county average. A Clintonville bungalow and a Grove City slab ranch can read very differently, and EPA's Citizen's Guide is clear that only a test of your own house answers the question.

Licensing and permits

State license: in Ohio, radon testing and mitigation for pay is licensed work under the OAC 3701-69 rules (see OAC 3701-69-04). Every Columbus bid should carry two ODH license numbers, one for the company and one for the specialist doing the design.

Before signing, look the company up in the state's radon licensure list, published as open data, which shows license type and expiration.

Building and electrical permits: Columbus and the suburban cities each run their own permit desks, and a dedicated fan circuit can trigger an electrical permit. Where a permit applies, HomeGuide's survey lists radon permit costs of $25 to $150.

Rental property: ask the mitigator for the post-mitigation test report in writing; EPA's Consumer's Guide recommends a retest within 30 days of installation and no sooner than 24 hours after the fan starts.

Local conditions

Why Columbus runs high: according to the Ohio Department of Natural Resources Geological Survey, the glaciers that flattened this part of Ohio ground up uranium-bearing Ohio Shale and spread it through the till, and the sand and gravel they left behind give soil gas an easy path upward. Franklin County homes are built almost entirely on those glacial deposits, along with river sand and gravel in the Scioto and Olentangy valleys.

The ring of counties around Columbus is just as high in the ODH data: south of the city, Pickaway shows 52.99% (of 1,472 tests) and Fairfield 52.89% (of 7,580); to the west, Madison shows 52.59% (of 1,234) and Union 43.11% (of 4,094); to the north and east, Delaware shows 49.64% (of 23,086) and Licking 51.08% (of 11,407), all as shares at or above 4 pCi/L.

ODH lists the county's single highest reading at 904 pCi/L. Readings like that are rare, but they show why a neighbor's low number says little about your own basement.

What drives local prices

Poured-basement homes in Dublin, Hilliard and Westerville most often get a single suction point through the basement floor, which HomeGuide's February 2026 cost survey puts at $1,200 to $2,000 installed (national average $1,600).
Older Columbus homes with hollow block foundation walls may need block-wall suction, $1,800 to $3,000 in HomeGuide's survey, often paired with a slab point.
Slab-on-grade ranches and split-levels can need a second suction area; in our calculator a mixed foundation carries an est. ×1.5 and a large house (2,500-plus sq ft) an est. ×1.25.
A professional post-mitigation test runs $125 to $400 and a do-it-yourself kit $10 to $30, per HomeGuide.
EPA's 2010 guide put yearly fan electricity and heating loss for a sub-slab system at $50 to $200 (2010 dollars), a running cost to weigh alongside the bid.

Common jobs

Single-point floor systems in the big suburban subdivisions of Dublin, Hilliard, Westerville and New Albany.
Block-wall plus slab systems in pre-war Columbus neighborhoods such as Clintonville, German Village and the University District.
Inspection-period testing and quick fixes during home sales in Upper Arlington, Bexley and Worthington.
Adding a fan to a builder's passive vent pipe, and sealing sump pits, in recently built neighborhoods.

From test to fixed, and where we cover

Step 1: run a test (yours or a licensed tester's) in the basement or lowest room you use. Step 2: if it reads 4 pCi/L or higher, follow EPA's advice and confirm it with a second test.

Step 3: ask two licensed Ohio mitigation companies for itemized bids and check them against the calculator. Step 4: once the fan has been on for a full day, test again to prove the result.

We cover Columbus, Dublin, Westerville, Hilliard, Grove City, Upper Arlington, Gahanna, Reynoldsburg, Worthington, Bexley, Whitehall, Groveport and Canal Winchester, along I-70, I-71, I-270, US 23, US 33 and SR 315.

Communities: Columbus, Dublin, Westerville, Hilliard, Grove City, Upper Arlington, Gahanna, Reynoldsburg, Worthington, Bexley, Whitehall, Groveport, Canal Winchester

Before you sign

A high result means planning a fix in the coming weeks, not an emergency call (EPA Citizen's Guide). Confirm the result, check the ODH license, and get the guarantee and fan warranty in writing.

Questions about Franklin County

How common is high radon in Franklin County, Ohio?

ODH's dashboard shows 44.88% of the county's 114,203 tests at 4 pCi/L or above.

Is Columbus higher or lower than the suburbs around it?

ODH reports by county, not city. Every neighboring county in the ODH file shows between 43.11% and 52.99% of tests at or above 4 pCi/L, so the whole region runs high.

Who can install a radon system in Columbus?

A company holding an Ohio radon mitigation contractor license, with a licensed specialist on the job; the rules are in OAC 3701-69.

What does a system cost in Franklin County?

Plan on $1,200 to $2,000 for a standard floor system and $1,800 to $3,000 if the block walls need suction, per HomeGuide's 2026 figures.

Sources

Related radon guides

Rules and fees change; confirm with the state radon office. Price your own system with the radon mitigation cost calculator, read the radon mitigation cost guide, or check any ZIP with the radon levels by ZIP tool.