Which radon test should I use?

The chooser below asks what you are testing, how soon you need an answer, what you can spend and whether you want readings over time, then names one test and what to do with its result. Every rule it follows is EPA's testing guidance, set out section by section further down this page.

EPA's testing steps start with a short-term test. It is the quickest way to check a home. The radon testing guide walks through the whole process with its diagrams; here is the short version. Every radon test should run for at least 48 hours, and some devices need longer, such as a 7-day charcoal canister. What you do next depends on the number.

1. 1

   Run a short-term test

   At least 48 hours, in the lowest lived-in level, with the house closed.

2. 2

   Below 4 pCi/L?

   No fix is called for. You may want to test again sometime, and always after major renovations.

3. 3

   4 pCi/L or more?

   Follow up: a long-term test for your year-round average, or a second short-term test if you need an answer soon.

4. 4

   Decide on the follow-up

   Fix the home if the long-term result, or the average of the two short-term tests, is 4 pCi/L or more.

If the first short-term result is more than twice EPA's 4 pCi/L action level, take a second short-term test right away. The higher your short-term results, the more certain you can be that the home needs fixing.

A continuous monitor is an active device: it runs on power and records radon over time, usually with hourly readings and an average for the test period. Professional monitors are a different class from consumer ones. Professional continuous monitors need yearly calibration and certification, are run by a trained operator, and are often used in real estate sales.

Consumer radon monitors are sold for home use. There is limited information on how accurate and precise low-cost monitors are, and their accuracy can be affected by where the monitor sits in the room, how long it has been in use, temperature and relative humidity. EPA does not recommend or endorse specific low-cost monitors. If your monitor reads above 4 pCi/L, follow up with a long-term test or talk to a radon professional. A monitor is a good way to watch a level over time; a decision to fix is made on an average, from a long-term test or two short-term tests.

1. 1

   Place it like a test

   In the lowest lived-in level, at least 20 inches above the floor, away from drafts, high heat, high humidity and exterior walls.

2. 2

   Give it time

   Read the average over days or weeks, not a single hour; radon varies from day to day and season to season.

3. 3

   Check a high reading properly

   If the average is above 4 pCi/L, follow up with a long-term test or talk to a radon professional before you decide to fix.

4. 4

   Test again after a fix

   Run a two- to seven-day test within 30 days of installing a system, then retest at least every two years.

Test within 30 days of installation, but no sooner than 24 hours after the system starts running with the fan on. A two- to seven-day measurement shows whether the system works. The contractor may test to check the work, and an independent follow-up measurement is recommended too: having an independent tester do it, or doing it yourself, removes any conflict of interest with the installer. After that, retest at least every two years. A fan monitor shows suction in the pipe, not radon, so only a test tells you the system is still keeping the level down.

You can test your home yourself or hire a qualified radon test company; either way, use a device from a qualified laboratory. In a sale, buyers often want the test made by someone who is not involved in the sale.

Testing is easy and inexpensive, and your state may offer free or discounted kits. A professional test costs more: Virginia's health department puts it at $100 to $200. Check the free and low-cost kit finder for your state, and the radon testing cost page for every published price.

Test in the lowest lived-in level of the home (the basement if it is used often, otherwise the first floor), at least 20 inches above the floor, away from drafts, high heat, high humidity and exterior walls. Do not test in a closet, stairway, hallway, crawl space, or an enclosed area of high humidity or fast-moving air.

A home on a private well may need a second kind of test. Testing water takes different devices and procedures from testing air, and although radon gets into some homes through water, test the air first. Vermont's health department sells a radon in water test kit for $25 from its laboratory; the radon water treatment cost page explains what a high result leads to.

Radon levels tend to vary from day to day and season to season. Opening the house changes them too: opening windows, doors and vents on the lower floors can lower radon, but once they are closed, levels most often return to where they were within about 12 hours. That is why tests are run under closed-house conditions, and why a single high or low reading is not your average.

Readings move for several reasons, and only some of them are real changes in your home's radon:

• Day to day and season to season, radon itself varies, so two short tests a month apart can differ.
• Opening windows, doors and lower-floor vents lowers the level for a while; once they close, it most often returns within about 12 hours.
• Unusually severe storms and high winds can upset a test of just 2 or 3 days, which is why those short tests should avoid them.
• Placement matters: drafts, high heat, high humidity and exterior walls all affect a reading, so test away from them.
• A consumer monitor's own accuracy can change with where it sits, how long it has been in use, temperature and relative humidity.

It follows that the longer the test, the better the result reflects your home's radon levels and the way you live in it. If a monitor's readings swing, read the average over days or weeks, and confirm a decision with a long-term test where you can.