Radon testing costs $125 to $400 on average for a professional radon inspection. However, costs may reach $700 for large, multi-story homes that require multiple testing devices.

Most radon inspectors use an electret ion detector, which features a statically charged Teflon disc that attracts ions generated by radon decay. These ions reduce the electrical charge of the disc, and the reduction can be measured in a lab to calculate the home's radon levels.

A home radon test kit costs $10 to $50, including professional lab analysis. Prices depend on whether you select a short-term or long-term test.

Radon is a natural colorless, odorless radioactive gas produced by the decay of uranium, radium thorium in the soil, rocks, and groundwater.

Because radon is present everywhere in the earth and the gas enters the air all around us, we are constantly exposed to it at very low levels as we breathe. These low levels are safe. However, exposure to higher levels is a health hazard and a common problem in residential homes.

Radon gas rises from the rocks and soil below your home's foundation and enters the home, where it becomes concentrated. Radon is carcinogenic, and prolonged exposure to these elevated levels of radon poses a serious health risk. Radon is the number one of lung cancer cause among non-smokers.

Radon can also be more dangerous to children than adults even if they are exposed to the same levels for the same length of time.

Short-term radon testing takes 2 to 7 days on average. The test should be left untouched for a minimum of 48 hours. Most DIY home test kits are short-term tests, and professional radon inspectors typically start with a short-term test before moving on to long-term testing.

Long-term testing takes 90 days to 1 year, depending on the test type. Because radon levels fluctuate daily and seasonally, long-term tests provide a more accurate picture of the average radon levels in your home.

Radon testing is highly recommended because elevated levels of radon are harmful to your health. According to the EPA, at least 1 in every 15 homes in the U.S. has levels of radon that exceed the maximum recommended amount. In regions that are more prone to radon, as many as 1 in 3 homes may have dangerous levels.

High levels of radon can occur in both old and newly constructed houses, and in any location. A house may have elevated radon levels even if the houses directly to each side of it do not. Radon testing is the only way to confirm the levels in your home.

The Environmental Protection Agency (EPA) recommends testing your home every 2 years or after any major renovations. For the best results, test your home during alternate seasons because radon levels vary throughout the year due to changes in air pressure and soil moisture.

Long-term radon testing kits provide precise results in over 95% of cases and are the most accurate option because radon levels fluctuate daily and seasonally.

Short-term tests provide an accurate picture of radon levels during the limited testing window of 2 to 7 days. However, this snapshot is not a good reflection of the radon levels throughout the year. A short-term test performed during the summer may indicate low radon levels even though levels are elevated in the winter.

When using a short-term radon test, repeat the test at least once or twice during other seasons of the year to get a more accurate picture of your home's average radon levels.

When evaluating radon testing and inspection companies near you, it's important to choose a specialist who is certified by at least one national radon agency. Follow these guidelines:

• Look for companies that specialize in radon inspections and/or home inspectors with radon certifications.
• Select companies certified by the National Radon Safety Board (NRSB) or the National Environmental Health Association (NEHA).
• Choose licensed, bonded, insured inspection companies that have been in business 5+ years.
• Check out their reviews on HomeGuide and Google.
• Beware of companies offering free radon testing if they also provide mitigation services, as they may try to pressure you to install a mitigation system even if it isn't necessary. Perform your own DIY home radon test to confirm their results.

Ask these questions when evaluating radon inspection companies:

• How long have you been in business?
• Are you NRSB or NEHA certified?
• What type of radon test device will you use in my home?
• How long will the test take?
• Where will you place the testing device?
• Will my home require multiple testing devices?
• What should I do to prepare my home before the test?
• Can I enter my home during the test?
• Is there anything I shouldn't do in my home during the test?
• What happens if the test shows high levels of radon in my home?