Testing for Radon Gas

Radon Testing
Safe family living space should be free of invisible and odorless radon gas. Testing for radon levels is the first step in creating healthy indoor air for your home.

Radon is a product of the decay of radium. When it breaks down, it produces radioactive particles that cling to dust and other materials. How and why radon concentrates in a house depends on several factors: house design, soil conditions, and weather conditions including barometric pressure and winds. Radon moves through the earth and rock beneath a house and is drawn into the basement or lowest level through cracks, unsealed pipe holes, sumps, exposed dirt floors, slab joints, or porous block walls.

Radon Concerns
If radon is present in the home, kids playing in the lower-level family room or those engaged in hobbies or business activities in the basement breathe in radon gas. While some radon particles are coughed out or swallowed, others rest in the lung tissue. There they release radioactive energy that destroys or damages cells. Mutated cells then go on to cause cancer or other diseases.

Approximately 20,000 people die each year in the United States from lung cancer due to radon exposure in their homes. Radon is the leading cause of lung cancer among nonsmokers.

Measuring Radon
Radon’s radioactivity is measured in units called picocuries, a measure that is fine enough to measure the disintegration of radioactive atoms in the air. By scientific measures, a house that has 4 picocuries of radon per liter of air has about nine atoms of radon decaying every minute in every liter of air in the house. A 1,000-square-foot house with 4 pCi/L of radon has nearly 2 million radon atoms decaying in it every minute.

The Environmental Protection Agency reports that the average indoor radon concentration is about 1.3 pCi/l of air. However, indoor radon levels of 5-50 pCi/l — even up to 2,000 – have been found. The EPA recommends fixing homes with radon levels at or above 4 picocuries per liter (pCi/L). 

Radon Test Results


Radon Testing Reminders:

Make sure the test kit purchased is not outdated.

Follow the proper protocol especially regarding the start and end times of the test and promptly send the device to the laboratory.

For a short-term test of a week or less, keep all windows closed, keep doors closed except for normal entry and exit, and do not operate fans or other machines which bring in air from outside for at least 12 hours before the start and during the entire test period.

If a reading is close to or just above 4.0, consider taking another test and averaging the scores of the two.

Be aware that weather conditions can affect testing. If the test days you planned include gusty winds or heavy rain, either do the test longer or redo the test when the weather is calmer. Barometric pressure and wind can affect the negative pressure in the house.


Michael Murphy, health physicist for Region 5 of the EPA, says 20 to 25 percent of the homes in the United States have been tested. About one in 15 homes nationally, or 61 percent, will have a problem, but results vary around the country. In Illinois, about one home in nine, or 11 percent of homes have high radon levels while in areas of Minnesota, 40 percent of homes tested have a problem. Even mobile homes, with the crawlspace-like area created by skirting, can have a radon problem.

Testing for radon has become common practice in real estate transactions, says Stephen Gladstone of Stone Hollow Inc., Stanford, Conn., former past president of American Society of Home Inspectors. “But it’s just as important to test if you plan to remain in a house,” he says. The rule of thumb is to test now and retest every three to five years or if remodeling has disrupted the soil around the home.

Radon Test Types
Tests of two to seven days can give a short-term snapshot of conditions in a home and are available for $5 to $30 from retail outlets and some state agencies. Most are as simple as setting out the test device for the required time and then sending it to a lab. Test results are mailed back within a week or two.

One common test device is a small metal container with activated charcoal that absorbs the radon in the air. The lab measures the decayed products and determines the concentration of radon in the air. These test are quick and inexpensive, but can have results that are off by as much as 20 percent. Testing labs often recommend repeating the test or running two tests simultaneously.

An alpha track test is left in place for three months to a year and is much more precise. One important key, however, is remembering where the return envelope is stashed!

Another option is to have a professional test with electronic equipment and computerized results. These tests are only performed by professional radon-testing firms, are much more expensive, but give almost immediate results. Be sure to check for credentials and certification when hiring a professional radon specialist. Some states have standards for these businesses, others do not.

Credit: Renovate Your World