This time of year, many people are spending a lot more time indoors. With windows and doors shut tight, you could be putting your family at risk for radon poisoning.

Radon is responsible for about 21,000 lung cancer deaths each year in the United States.

Radon comes from the breakdown of uranium in rocks and soil. It's a radioactive gas in the air we breathe, but it becomes unsafe when the gasses are trapped indoors.

It's a hidden danger that could be in your home and why officials want residents to find out if they are affected.

"It is an odorless, colorless gas and it has no taste so short of testing for it there is no way to know whether or not there's an issue," said Sabrina Novak, with the Chattanooga-Hamilton County Health Department. "It enters the home through cracks and openings, and all homes regardless of age, energy-efficiency, or foundation type are at risk. The only way to know is to test that home," she explained.

A device inside Kyle Stephens' home offers his family peace of mind.

"We have a two-year-old and one on the way and we want to make sure those growing lungs didn't have any exposure to radon," Stephens said.

Radon occurs in every county in Tennessee with Hamilton County specifically at a moderate risk.

Those who smoke not only incur damage to the lungs from tobacco, but they are also exposed to the constant background of radon in the atmosphere, placing them at an even higher risk than non-smokers.

"There's the potential to develop lung cancer and it is the leading cause of lung cancer in non-smokers and if you're a smoker and you're exposed to high levels of radon, it actually increases your chances of developing lung cancer," Novak said.

Sixteen Tennessee counties have low risk, 46 face a moderate risk, and 33 are classified as having a severe risk.

Malcolm Godwin with Chattanooga Home Inspectors said levels can vary due to earth structure and geologic makeup.

"So the thing about radon is you can have high levels in your house and your next door neighbor can have low levels," Godwin said.

Testing helps you know if you have radon in your home. Test your home or business with the free kit from the Tennessee Radon Program, operated by the Tennessee Department of Environment and Conservation (TDEC).

Structures should be retested every 3-5 years. Flooding and saturated ground can produce artificially lower test results. The results can be emailed to the owner.

You can also buy one for less than $20 at area hardware stores. Both tests will notify by email with your test results.

The EPA says if your test reaches a "four," steps need to be taken. Stephens' test came back dangerously high.

"We were a little freaked out because you know anything over a four you're supposed to mitigate and it came back as an eight," he said.

Officials say you should test again to verify the reading and hire a professional to correct he issue.

"It shows a graph of when it peaked and when it was at lower points," Godwin said.

Godwin showed us a machine they use to take a more accurate reading over a 48-hour-period. It showed a 1.7 inside the Stephens home, 6 points lower than the take-home test.

Godwin explained the family is safe, but there are steps to take if a reading is higher.

"A vent with a fan that runs 24-hours a day, 7 days a week and just pulls a little bit of that stagnant low lying air from the bottom of the foundation and delivers it outside the house," he explained.

It's news this father is relieved to hear, but he hopes others will be aware of the risks.

"It's not that expensive compared to what could happen with the medical issues and losing years on your life and the biggest thing is peace of mind," Stephens said.

Georgia has lower levels of radon compared to Tennessee, but that doesn't mean your home is not at risk. The University of Georgia offers test kits for Peach State residents.

Tennessee resident can visit the Tennessee Radon Program for a free kit.

If radon levels are determined dangerous in your home, you should contact a qualified contractor who specializes in radon mitigation. It is suggested to use contractors certified or trained by either the National Radon Proficiency Program or the National Radon Safety Board.

In any case, it's best to check with the Better Business Bureau, get references, and obtain several bids.