Radon Testing at Home, Step by Step

The kit goes in the lowest level of the house that people actually live in: the basement if the family uses it often, otherwise the first floor. Pick a room that gets regular use, such as a living room, den, playroom or bedroom, but never the kitchen or bathroom.

EPA's placement rules are specific. Set the kit at least 20 inches above the floor, where nobody will knock it over, and keep it away from drafts, high heat, high humidity and exterior walls. If you later start using a lower floor, such as a newly finished basement, test that level too. EPA also says to test before a major renovation and again once the work is done, because remodeling can change how soil gas reaches the rooms.

Closed-house conditions mean keeping windows and outside doors shut as much as possible for the whole short-term test, apart from normal coming and going. Fresh outdoor air dilutes radon, so an open window during the test can give you a falsely low number.

For a test lasting only 2 or 3 days, EPA adds a lead-in: close windows and outside doors at least 12 hours before you start, so the house is already closed before a 2–3 day test begins. Your heating or cooling system's fan may run as long as it only recirculates indoor air. Don't run fans or other machines that pull in outdoor air, such as a whole-house ventilation system set to bring in fresh air or a window fan. Short bursts of a bathroom or kitchen exhaust fan are fine, and so is the fan of an existing radon system.

Hire a tester when you are buying or selling a home, or when you simply prefer not to handle the kit yourself. EPA says buyers often want a measurement made by someone with no stake in the sale, and a professional's device and paperwork answer that need.

Look for a measurement professional credentialed by one of the two national programs EPA currently recognizes, the National Radon Proficiency Program or the National Radon Safety Board, or licensed by your state where the state licenses testers. Your state radon office can supply names; EPA keeps a list of state radon contacts by region. Ask which device they'll use and how long it runs.

Retest whenever something changes the way the house sits on the soil or the way you use it. EPA lists the triggers: moving living space down to a lower floor, before and after major renovations, and after any radon system is installed.

Even a low result isn't permanent, and EPA notes you may want to test again sometime in the future. Homes with a working radon mitigation system should be retested at least every two years. New homes built with radon-resistant features still need a test after move-in, because the features don't promise a low number. If you're unsure, call a licensed pro.