Radon Map Ohio: What Homeowners Need to Know
If you live in Ohio and have started looking into radon, you have probably found the EPA radon map and seen a lot of red. Ohio is one of the higher-risk states in the country, with most of its counties classified in the highest tier. A radon map is a useful starting point, but it describes county-wide averages, not your specific house — and that distinction matters more than most homeowners realize. This guide explains how to read the Ohio radon map, why it cannot substitute for a test, and what to do with the information. It summarizes EPA guidance current as of 2026 and is educational only — test your own home and consult a certified professional for results that matter.
Part of our Radon Levels guide — start there for the full picture →
What does the radon map of Ohio show?
The EPA radon map divides the country into three zones based on predicted average indoor radon levels. Zone 1 counties have a predicted average at or above 4.0 pCi/L — the EPA’s action level. Zone 2 falls between 2.0 and 4.0 pCi/L, and Zone 3 is below 2.0 pCi/L. On the Ohio map, the large majority of counties fall into Zone 1, with most of the rest in Zone 2 and very few in Zone 3. In plain terms, Ohio is a high-radon state.
The map reflects Ohio’s geology: glacial deposits and uranium-bearing soils across much of the state generate radon that seeps into homes. But the zone color tells you the county’s predicted average, not the reading inside any one home. Two houses in the same Zone 1 county can test very differently, which is the central limitation of any radon map. Our explainer on the EPA radon map and how to read it covers the zone system in more depth.
It helps to understand how the map was built. The EPA developed it using indoor radon measurements, geology, aerial radioactivity data, soil characteristics, and foundation types, then assigned each county to a zone based on the predicted average for that area. The result is a planning-level snapshot, deliberately generalized to the county scale. That generalization is its strength for directing public-health resources and its weakness for answering the question a homeowner actually has, which is about one specific house.
Why maps cannot replace testing
A radon map is a planning tool, not a diagnosis. The EPA is explicit that the maps were designed to help governments and builders target resources, not to determine whether an individual home needs mitigation. The only way to know your home’s level is to test it.
The reason is that radon entry depends on house-specific factors the map cannot capture: foundation type, the number and size of cracks and openings, how the home is sealed, soil directly beneath the structure, and how the heating system moves air. A home in a low-risk Zone 3 county can still test high, and a home in a Zone 1 county can test low. Relying on the map alone — in either direction — is a mistake. Our guide to radon readings in homes explains how much variation is normal.
Consider two homes on the same Ohio street. One has a tightly sealed basement with a sump pit and numerous slab cracks, and a furnace that depressurizes the lower level; it might test at 8 pCi/L. The neighbor, with a slab-on-grade foundation, few openings, and balanced ventilation, might test at 1.5 pCi/L. The county map shows both as the same color. Only an individual test distinguishes them, which is why the EPA’s guidance for homeowners is unambiguous: test, regardless of what the map shows.
How Ohio compares — and why Colorado readers should care
Ohio and Colorado share something important: both are heavily Zone 1 states. The Colorado Front Range, like much of Ohio, sits in the highest-risk tier, where the predicted indoor average exceeds 4.0 pCi/L. The EPA names radon the second-leading cause of lung cancer and the leading cause among people who never smoked, so the stakes are the same in both places.
The lesson transfers directly. Whether a homeowner is in Cincinnati or Castle Rock, the map signals elevated regional risk, but the individual test is what determines action. Front Range readers can think of the Ohio map as a mirror of their own situation, and our overview of states with the highest radon levels shows where both states rank.
The geology differs even where the risk rating matches. Ohio’s radon comes largely from glacial till and shale deposits left across the state, while Colorado’s stems from the uranium-rich rock and soils of the mountains and foothills. The mechanism that brings the gas indoors, however, is identical everywhere: radon produced in the ground rises and enters buildings through the foundation. That shared mechanism is why the same testing and mitigation approaches work in both states despite their different underlying rock.
Local variation within a state
Even within Ohio, the map shows meaningful variation. Counties in the central and western parts of the state tend toward the highest readings, while some areas read lower. This patchwork holds in Colorado too, where the Front Range counties cluster in Zone 1 but specific neighborhoods and even individual lots can differ based on the soil and rock directly beneath them. A county-level color smooths over all of that local detail.
The takeaway for a homeowner is to resist drawing comfort from a neighbor’s test or a favorable-looking corner of the map. Radon is a hyper-local phenomenon at the scale of a single foundation. The soil under your house, the cracks in your slab, and the way your home pulls air are what set your level, and none of those appear on any map. Testing your own home is the only way to replace the map’s broad estimate with a fact.
Reading the map without overreacting
A red Zone 1 county can look alarming, but it is not a verdict on your home. It means testing is strongly warranted, not that your home is definitely dangerous. Equally, a Zone 2 or Zone 3 color is not permission to skip testing — those zones still see plenty of elevated homes.
The practical reading is simple. Use the map to understand that radon is a real regional concern worth taking seriously, then test your own home to learn your actual number. The map sets expectations; the test sets facts. No homeowner should mitigate based on a map alone, and none should feel safe based on a map alone either.
Newer radon potential maps and tools
The original EPA zone map dates to the early 1990s, and while it remains a useful reference, more detailed tools have emerged since. Some states, including Ohio, publish their own radon data at finer resolution, sometimes down to the zip code, drawing on the thousands of home tests collected over the years. These newer datasets give a more granular sense of local risk than the three-zone county map.
Even the best of these tools, however, shares the original map’s fundamental limitation: it describes an area, not a house. A zip-code-level map showing a high local average still cannot tell you whether your particular foundation and soil produce a high reading. The improved resolution sharpens the regional picture and can strengthen the case for testing, but it does not replace the test itself. Treat any radon map, old or new, county-level or zip-code-level, as a prompt to measure your own home.
What to do after checking the map
The next step is always the same: test. Start with an inexpensive short-term kit or a continuous monitor, placed in the lowest lived-in level under closed-house conditions. If the result is at or above 4.0 pCi/L, confirm with a second test or a professional measurement, then consider mitigation.
Test during the heating season when levels run highest, and re-test every two years and after major renovations. For Ohio homeowners specifically, contacting the state radon program can point toward low-cost test kits and certified professionals; Colorado offers similar resources through its state health department.
Choose the test type to match your goal. For a quick answer about whether the home has a problem, a short-term kit run over several days is enough. For the truest picture of long-term exposure, a long-term detector or a continuous monitor running across seasons captures the full range, including the high-radon winter months. Either way, the act of testing is what converts the map’s broad regional estimate into a number specific to your home, and that number is the only one that should drive your decisions.
What if your test comes back high?
A high reading is common in Zone 1 areas and is highly fixable. The standard solution is an active soil depressurization system — a pipe and fan that draw radon from beneath the foundation and vent it above the roof, routinely cutting levels by 80 to 99 percent. The process is the same regardless of state. Confirm the fix with a post-mitigation test below 4.0 pCi/L, and keep a continuous monitor running for ongoing assurance.
A high reading is not a reason to panic or to question the home itself. In Zone 1 areas like much of Ohio and the entire Colorado Front Range, elevated radon is a function of geology, not of poor construction or neglect. The same well-built home can read high simply because of the soil beneath it. Treating a high result as a routine, solvable maintenance item — rather than a flaw in the house — keeps the response measured: test, mitigate, verify, and move on.
Using the map as a conversation starter
The most productive way to use any radon map is as a prompt for action rather than a final answer. If the Ohio map — or the Colorado map — shows your county in Zone 1, let that be the nudge to order a test, talk to a neighbor who has tested, or contact your state radon program for a low-cost kit. The map’s job is to make radon visible as a regional concern; your job is to turn that awareness into a measurement of your own home.
State radon programs in both Ohio and Colorado offer resources to help, from discounted test kits to lists of certified professionals. A homeowner who notices the map, requests a kit, and tests has used the tool exactly as intended. The mistake is to look at the map, feel either alarmed or reassured, and stop there. The color on the map is the beginning of the process, not the end, and the test is what converts a broad estimate into the fact you can act on.
When to call a professional
Call a certified radon professional when a test reads at or above 4.0 pCi/L, when buying or selling a home and you need a defensible measurement, or when you want a calibrated confirmation of a borderline home result. Look for certification through AARST-NRPP or NRSB in any state. The radon map — whether for Ohio, Colorado, or anywhere — is where you start the conversation, but a certified test and a professional’s read are what turn a map color into a clear decision.
References
- EPA Map of Radon Zones and State Contacts — U.S. Environmental Protection Agency
- A Citizen’s Guide to Radon — U.S. Environmental Protection Agency
- Health Risk of Radon — U.S. Environmental Protection Agency
Frequently asked questions
Is Ohio a high-radon state?
Yes. The majority of Ohio counties fall into EPA Zone 1, the highest-risk tier, with a predicted average at or above 4.0 pCi/L. Ohio's glacial and uranium-bearing soils make elevated radon common across much of the state.
Can I rely on the radon map instead of testing?
No. The map shows county-wide predicted averages, not your home's level. Homes in low-risk counties can test high and vice versa. The EPA says the only way to know your home's radon is to test it.
How does Ohio compare to Colorado for radon?
Both are heavily Zone 1 states. The Colorado Front Range, like much of Ohio, sits in the highest-risk tier where the predicted indoor average exceeds 4.0 pCi/L, so homeowners in both places should test.
What should I do if my home tests high?
Confirm an elevated result, then consider mitigation. An active soil depressurization system with a pipe and fan routinely cuts radon by 80 to 99 percent. Verify the fix with a post-mitigation test below 4.0 pCi/L.
A radon map only points the way — your home’s number comes from a test. If you’re on the Colorado Front Range and want a certified measurement, get in touch through our contact page and we’ll connect you with a vetted local radon professional.
Test your home for radon
Radon is invisible and odorless, so a test is the only way to know your level. A short-term kit gives a first reading in days; a digital monitor tracks it over time.
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