How long does a radon test take?

Short-term tests run from 2 to 90 days, and most kits sold for homeowners run 2 to 7 days. Long-term tests run more than 90 days and give a better picture of what you breathe over a year.

Can I test during a home sale?

Yes, and most buyers do. Sale tests are usually short-term and often use a continuous electronic monitor placed by a certified measurement professional, so the seller can't easily skew the result.

Should I test in summer or winter?

Either works for a first look, but levels tend to run higher in the heating season when the house is closed up. A low summer result is worth confirming with a winter test.

My first test was 4.2. Do I need a system?

Run a second test first. If you used a short-term kit, a follow-up short-term or a long-term test tells you whether 4.2 was typical or a spike.

Radon Testing in Mansfield, MA | Certified Radon Solutions

Short-term or long-term

There are two kinds of tests, and they answer slightly different questions.

A short-term test runs from 2 to 90 days. Most hardware-store kits are charcoal canisters meant for 2 to 7 days. You open it, set it out, seal it back up when time’s up, and mail it to the lab. It tells you what the air was like during those few days.

A long-term test runs more than 90 days. Radon moves around with the weather, the season, and how you run the house, so a long test smooths out the swings. If you have the time, it’s the better read on what your family actually breathes.

Most people start with a short-term kit because it’s fast. That’s fine. Just treat one short result near the line as a first look, not a verdict.

Where to put the kit

This is where most tests go wrong.

Put it on the lowest floor you actually use. A finished basement where the kids watch TV counts. A crawlspace or an unfinished storage basement you never sit in doesn’t.
Keep it about 20 inches off the floor, away from exterior walls and at least a few feet from windows.
Stay out of kitchens, bathrooms, and laundry rooms. Humidity and fans throw off the reading.
Don’t set it next to a sump pit, a floor drain, or a heat register.

Closed-house conditions

For a short-term test, keep windows and exterior doors shut for at least 12 hours before you start and for the whole test. Normal coming and going is fine. Run the heat or central air as you normally would, but don’t run window fans or a whole-house fan that pulls in outside air.

If a storm or high wind rolls through during the test, note it. A strong nor’easter can push numbers around for a day or two.

Reading the result

The lab reports radon in picocuries per liter, written pCi/L.

Under 2 pCi/L. No action needed. Retest every few years or after you finish a basement or change the heating system.
2 to 4 pCi/L. EPA says to consider fixing. Many people retest with a long-term kit to see where the level really sits.
4 pCi/L or higher. EPA recommends fixing the home. Confirm with a second test, then read our guide to what a radon mitigation system involves.

Doing it yourself or hiring it out

A homeowner kit is fine for your own information. For a real estate deal, or if the result is going to decide whether you spend money on a system, a certified measurement professional is the better call. They use continuous monitors that log hourly readings and flag tampering.

Massachusetts doesn’t certify radon testers itself. DPH recommends choosing someone certified by NRPP or NRSB. Our page on finding a certified radon professional shows where to look them up.

Don’t forget the water. If your home is on a private well, an air test alone doesn’t tell the whole story. See radon in well water.

Back to the Mansfield radon guide.

How to test a Mansfield home for radon