The state Department of Public Health on Tuesday urged Connecticut residents to test their homes for radon gas, the leading cause of lung cancer in nonsmokers.

The health department’s Radon Program recommends that all Connecticut homes be tested for radon. Testing is recommended in the winter and the process is simple and inexpensive, the health department said.

Connecticut residents may obtain a free radon test kit by completing an online form at www.ct.gov/dph/radon. Test kits will be available only during January, and while supplies last. Test kits also can be purchased from the American Lung Association of New England by calling (800) 586-4872 or at a local hardware store.

Health officials estimate that radon is responsible for more than 21,000 lung cancer deaths each year in the United States, the health department said in a news release.

Radon is an invisible gas that has no smell and people often don’t know when this silent killer is in their homes. That is why testing for radon and reducing elevated levels is so important — it saves lives.

The U.S. Environmental Protection Agency recommends that homes with radon levels at or above 4.0 pCi/L be fixed. Homeowners should consider reducing their potential lung cancer risk by fixing homes with radon levels between 2 pCi/L and 4 pCi/L. Smokers exposed to radon have a much higher risk of developing lung cancer.

Radon problems can be corrected by qualified radon contractors, with costs typically ranging between $1,200 and $1,500. A homeowner should hire a qualified radon mitigation contractor to decrease airborne radon levels.

For information and to obtain a list of qualified radon mitigation contractors, visit www.ct.gov/dph/radon.