How to read an Ohio radon test report, section by section

The test is over, and a PDF has landed in your inbox with one number in large type and several pages behind it. That number gets all the attention, yet the pages behind it decide whether it deserves your trust, and Ohio spells out exactly what those pages must contain.

The items every Ohio report has to list

The Ohio Radon Measurement Protocol, appendix A to Ohio Administrative Code rule 3701-69-07, sets both a deadline and a checklist. The report is due within 30 days of the devices being retrieved, or within 14 days of the lab returning results, and it has to show:

• Start and stop dates and times
• The device type and each serial number
• Ohio license numbers for whoever placed the devices and whoever collected them
• The laboratory that analyzed them, with its own Ohio license number
• Whether a mitigation system was in the house, and whether it was running
• Any tampering or departure from the protocol
• Severe weather during the test
• Exactly where each device sat, on a diagram or a form

A continuous monitor report adds hour-by-hour readings on top of all that. Before acting on the headline number, confirm every item on this list is actually on the page; a missing license number or a blank location is a question to ask first.

Start with the placement page

Location comes first because it decides whether the result can support a decision at all. The protocol wants the lowest level of the house that is suitable for occupancy, in a room people could use regularly. A reading from a bathroom, kitchen, laundry room, closet, crawlspace, or sump cannot be the basis for a decision. Within that room, the device belongs:

• Between 20 inches and 6 feet off the floor
• At least 3 feet from doors, outside windows, and vents
• At least 1 foot from exterior walls
• At least 4 feet from any heat source
• At least 10 feet from a sump pit
• Out of direct sunlight

Bigger floors need more devices: one more for every additional 2,000 square feet on the tested level. A split-level gets a test for each foundation type, meaning the basement, the room over the crawl, and the slab room. In a Clintonville bungalow the lowest livable level is usually the basement; in a Whitehall ranch on a slab it may be the main floor. If the diagram puts the monitor in the laundry room or on the sump lid, the result is information, not a verdict.

Reading the hourly numbers

A continuous monitor logs radon every hour, and the report either graphs those readings or lists them in a table. The figure that counts is the average across the whole test, not the worst hour. The shape of the curve still repays a minute of attention, because it shows whether the house behaved like a closed house. Patterns worth recognizing:

• A gentle daily wave: radon commonly builds overnight and into the early morning, when the gap between indoor and outdoor temperature pulls hardest on the soil, then eases in the afternoon. That is a house behaving normally.
• A rise that tracks the weather: a passing front, falling barometric pressure, or heavy rain soaking the clay till around a foundation can lift readings for a stretch. The report should note severe weather, and Ohio does not allow a test under 96 hours to run through severe storms or sustained winds of 30 mph or more.
• A sudden step down that holds for hours, then recovers: the usual signature of a window or door left open, or a fan carried into the room. It belongs in the deviations section.
• A flat line near zero, or a gap: the monitor may have been unplugged or moved. On a real-estate test the monitor needs 48 contiguous hours; the first 4 may be discarded, but removing data from the middle voids the test.

Judge the result by the average, and judge the test by the shape of the curve.

When two devices sit side by side

Some tests, including one of the two methods Ohio allows during a home sale, use a pair of passive devices placed 4 to 5 inches apart. Ohio checks whether the pair agrees using relative percent difference, which is the gap between the two results divided by their average, written as a percent.

• Both results under 4 pCi/L: they should agree within 67 percent
• Both results at 4 or above: they should agree within 36 percent
• One at 4 or above and the other under 4, with the higher more than twice the lower: you are told about the discrepancy and the test is repeated

Suppose one device reads 5.0 and its partner reads 6.0. The gap is 1.0 and the average is 5.5, so the difference comes to about 18 percent, comfortably inside the 36 percent allowance. The report shows each device's result along with the pair's average. Results from different rooms or floors are never averaged together; only collocated devices are.

What voids a short-term test

A report that flags a problem is doing its job. The ones that deserve suspicion are silent about something you know went wrong. These conditions undo a result:

• Closed-house conditions not held: for any test under 96 hours, windows shut and exterior doors used only for ordinary coming and going, starting at least 12 hours before the devices go out
• A whole-house fan in use, or a fireplace burning that is not the home's main heat
• Ceiling fans, dehumidifiers, humidifiers, air cleaners, or window air conditioners running within 20 feet of a device
• A measurement period under 48 hours
• A device in a room the protocol excludes

The heating and cooling system should run as usual, and a vacant house should be held near 72 degrees, give or take 5. If you opened windows during the test, say so; a retest is a smaller problem than a decision built on a bad number.

What the number asks you to do next

Outside a home sale, Addendum A of the protocol sets the next move by result:

• Under 4 pCi/L: no action required; retest in two years or after renovation
• From 4 up to 8: a second short-term test, or a long-term test to capture the year-round average
• 8 or above: a second short-term test, then decide on the average of the two

EPA adds that results between 2 and 4 pCi/L are still worth considering a fix, because risk does not stop at the action level. Any follow-up test goes in the same spot as the first, so the two results can be compared honestly. Match the second test to your timeline: a short-term test answers fast, a long-term test answers more completely.

The test result FAQ explains each band in plain terms, and the short-term vs long-term comparison helps you choose the follow-up. For a licensed retest run to the Ohio protocol, see how radon testing works across Central Ohio. Or work through our radon diagnosis guide to gauge how urgent your situation is, then call or text (380) 221-7233 with the report open in front of you.