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Testing for Radon

Radon graphic showing examples of short-term test devices
Environment, Great Lakes, and Energy

Testing for Radon

Since radon is tasteless, odorless, and colorless, it can't be detected with your senses. The only way to know whether your home has elevated radon levels is to test with a device specifically designed to detect radon.

Testing can be done with a do-it-yourself kit that you send back to a laboratory for analysis, or you can hire a professional to test for you. If you are willing to read and follow instructions, a do-it-yourself kit may be adequate. However, if you're involved in a real estate transaction, you may wish to hire a professional tester.

The first test you do is normally a short-term screening measurement. These tests need to be done under closed-house conditions, so the winter heating season is the ideal time to test. However, testing can be done at any time of year if closed house conditions can be met.

Short-term screening measurements are a minimum of 48 hours long, and would typically range from 2 to 7 days. However, they can last as long as 90 days, depending on the type of device being used.


Les Smith
800-723-6642 (800-RADONGAS)

Find a radon test kit

Test Conditions

It is very important that you read and follow the instructions that come with your test kit. Choose a location where you spend time and place the device:

  • in the lowest livable level,
  • at least 3 feet from windows, exterior doors, or other openings in foundation floor or walls,
  • at least 20 inches above the floor (preferably 3-6 feet above the floor, in the "breathing zone"),
  • at least 12 inches from exterior walls and at least 4 inches from other objects, and
  • where it won't be disturbed!

Test in the lowest livable level of the home, a basement if you have one. Choose a room where you spend time, such as a bedroom, living room, family room, den, or rec room. Avoid testing in kitchens, bathrooms, laundry rooms, closets, utility rooms, or crawlspaces.

For short-term tests (those lasting from 2 to 90 days), it is important that you also follow the requirement for "closed-house conditions." This means keeping all exterior doors and windows closed, except for normal entry and exit; attic fans off; and kitchen & bathroom fans off.

Testing Devices

3-7 Day Radon Test Kit

Activated Carbon (charcoal) Test Device

The most common and most readily available short-term screening measurement device is an activated carbon (charcoal) test device. This device may be a plastic or metal canister, a glass or plastic vial, or a paper pouch or envelope. The exposure period for these devices ranges from 2 to 7 days, depending on the manufacturer. They typically sell for $10-$20. The cost of charcoal devices often includes the postage and lab fees, but not always, so check before you buy!

Close up of rounded piece of equipment

Electret-Passive Environmental Radon Monitor

Another test device used for short-term screening measurements is an E-PERM (Electret-Passive Environmental Radon Monitor). This device is most often used by professional testers, but in recent years it has become more accessible to the average homeowner. You can "rent" one from a local tester, or you can deal directly with the manufacturer/laboratory via phone, mail, or e-mail to obtain a device.

Radon CRM Machine

Continuous Radon Monitor

Continuous radon monitors (CRMs) are electronic devices that require some sort of power source. Some are plugged into an electrical outlet, while others run on an internal battery. These radon detection devices come in various shapes and sizes. CRMs require annual calibration and certification and are used by a trained operator. CRMs are frequently used for measurements conducted in conjunction with a real estate transaction. The typical price for radon tests performed using CRMs is around $75 to $200.

Radon graphic showing an alpha track long-term testing device

Alpha Track Detector

Another device used to measure indoor radon levels is the alpha track detector. This small plastic canister can be used for time periods ranging from 30 days to one year. It requires no power source and is most often used as a year-long follow-up measurement when a moderately elevated radon level has been found using a short-term screening device. The one-year measurement provides an estimate of your average annual exposure, giving you a better idea of what you are actually exposed to on a long-term basis. It allows you to measure the radon level under normal living conditions over a relatively long period of time. As such, it takes into account all the changes in weather that occur throughout the year as well as the changes in the way you occupy/use your house under different weather conditions. Weather conditions and ventilation habits can influence the radon level in your house. With this test, you measure the way you actually live, opening and closing doors and windows any time you want, and using mechanical ventilation (i.e., furnace, air conditioner, exhaust fans, whole house fans, etc.) as you wish. The annual average exposure is a better estimate of your actual risk, but it is usually a follow-up to a short-term test and is rarely used as the initial measurement.