How to test your home for radon

Testing is the only way of knowing whether radon is in your home.^[1] Neighboring homes can have significantly different radon levels,^[2] so a neighbor's result can't stand in for yours.

Long-term testing is best

Radon levels can change daily, weekly and seasonally. That's why the Vermont Department of Health recommends a long-term radon in air test of 3 to 12 months, ideally including a heating season. Longer test periods give the most accurate measure of actual exposure.^[2]

The EPA explains the difference this way: short-term tests stay in a home for 2 to 90 days, and long-term tests stay for more than 90 days. A long-term result is more likely to tell you your home's year-round average.^[3]

When a short-term test makes sense

For a real estate transaction or another case where you need a quick answer, the Health Department Lab, private labs and building supply stores sell short-term kits.^[2] If you use short-term kits, the Health Department says to use two, placed side by side.^[1] See Buying or selling a home for the EPA's real estate testing options.

Setting up a test

These tips come from the EPA's guide for home buyers and sellers. Always follow the instructions that come with your kit.^[3]

• Test in the lowest level of the home that is or could be used regularly, finished or not.
• Don't test in a closet, stairway, hallway or crawl space, or in a kitchen, bathroom, laundry room or furnace room.
• Place the device at least 20 inches above the floor, where it won't be disturbed, away from drafts, high heat, high humidity and exterior walls.
• For short-term tests, keep windows and outside doors closed except for normal entry and exit. For tests shorter than four days, close them at least 12 hours before starting, and don't test during severe storms or high winds.
• Record the start and stop dates and times, then reseal the kit and send it to the lab right away.

Testing your water

If your home is on a private well or spring, radon in water can add to the radon in your air.^[5] See Radon in well water.

How often to test

• If your levels were low: retest every five years, or whenever you make significant changes to your home's structure or mechanical systems.^[2]
• If you have a mitigation system: test every two years to make sure it's still working.^[2]
• After a new mitigation system is installed: test again to make sure levels are below 4.0 pCi/L.^[2]
• Before and after finishing or renovating an unfinished area such as a basement, the EPA recommends a radon test.^[3]