You can’t see radon, but it’s not hard to find out if you have a radon problem in your home. All you need to do is test for radon. Testing is easy and should only take a few minutes of your time.

The amount of radon in the air is measured in “Pico curies per liter of air,” or “pCi/L.” There are many kinds of low-cost “do-it-yourself” radon test kits you can get through the mail and in hardware stores and other retail outlets.  If you prefer, or if you are buying or selling a home, you can hire a qualified tester to do the testing for you.  You should first contact your state radon office about obtaining a list of qualified testers.  You can also contact a private radon proficiency program for lists of privately certified radon professionals serving your area.

There are Two General Ways to Test for Radon:

SHORT-TERM TESTING:

The quickest way to test is with short-term tests. Short-term tests remain in your home for two days to 90 days, depending on the device. “Charcoal canisters,” “alpha track,” “electret ion chamber,” “continuous monitors,” and “charcoal liquid scintillation” detectors are most commonly used for short-term testing. Because radon levels tend to vary from day to day and season to season, a short-term test is less likely than a long-term test to tell you your year-round average radon level. If you need results quickly, however, a short-term test followed by a second short-term test may be used to decide whether to fix your home.

How To Use a Test Kit:

Testing is easy and should only take a few minutes of your time.

Follow the instructions that come with your test kit. If you are doing a short-term test, close your windows and outside doors and keep them closed as much as possible during the test. Heating and air-conditioning system fans that re-circulate air may be operated.  Do not operate fans or other machines which bring in air from outside.  Fans that are part of a radon-reduction system or small exhaust fans operating only for short periods of time may run during the test.  If you are doing a short-term test lasting just 2 or 3 days, be sure to close your windows and outside doors at least 12 hours before beginning the test, too. You should not conduct short-term tests lasting just 2 or 3 days during unusually severe storms or periods of unusually high winds.  The test kit should be placed in the lowest lived-in level of the home (for example, the basement if it is frequently used, otherwise the first floor). It should be put in a room that is used regularly (like a living room, playroom, den or bedroom) but not your kitchen or bathroom. Place the kit at least 20 inches above the floor in a location where it won’t be disturbed – away from drafts, high heat, high humidity, and exterior walls. Leave the kit in place for as long as the package says. Once you’ve finished the test, reseal the package and send it to the lab specified on the package right away for analysis. You should receive your test results within a few weeks.

LONG-TERM TESTING:

Long-term tests remain in your home for more than 90 days. “Alpha track” and “electret” detectors are commonly used for this type of testing. A long-term test will give you a reading that is more likely to tell you your home’s year-round average radon level than a short-term test.

EPA Recommends the Following Testing Steps:

Step 1. Take a short-term test. If your result is 4 pCi/L or higher take a follow-up test (Step 2) to be sure.

Step 2. Follow up with either a long-term test or a second short-term test:

• For a better understanding of your year-round average radon level, take a long-term test.
• If you need results quickly, take a second short-term test.

The higher your initial short-term test result, the more certain you can be that you should take a short-term rather than a long-term follow up test. If your first short-term test result is more than twice EPA’s 4 pCi/L action level, you should take a second short-term test immediately.

Step 3. If you followed up with a long-term test: Fix your home if your long-term test result is 4 pCi/L or more.  If you followed up with a second short-term test: The higher your short-term results, the more certain you can be that you should fix your home. Consider fixing your home if the average of your first and second test is 4 pCi/L or higher.

Source: http://www.epa.gov/radon/pubs/citguide.html#howdoes