Radon is a naturally occuring radioactive gas that is a byproduct of the atomic decay of radium in the ground. It has about a 4-day half-life, so the radioactivity of radon emitted a month ago is pretty close to zero today. But, while it is fresh, the radioactivity of the gas can damage your lungs and increase your risk of lung cancer. See our blog post How was it determined that between 15,000 and 22,000 lung cancer deaths each year are caused by radon? for a more complete explanation of the harmful effects of radon exposure.

    Because the density of radium deposits varies, the amount of radon generated and emitted into the air above also varies in different regions. So some areas have a higher likelihood of elevated radon levels. The map above of Marion County, Florida, shows a red area that encircles downtown Ocala that has a high liklelihood of elevated radon, for example. The yellow and green areas have progressively less probability. But a radon test result can vary wildly from house-to-house in any area. There are also other variables that can create short-term changes in the results of a radon test.

• Weather - Changes in outdoor temperature and wind direction affect the radon result. The change in barometric pressure and and ground saturation from rain during a thunderstorm will usually increase a radon test result, so it is not recommended to test during stormy weather.

• Time Of Year - Test results can vary seasonally, with the winter heating season tending to enhance the natural “stack effect” of a house. See our blog post Will opening the windows reduce the radon level in a house? for more on the stack effect.

• Length Of Test - Radon levels vary from hour to hour in a test. The graph below shows the hourly change of radon levels over a two-day standard test for a recent real estate transaction. Although the average was 3.5 pCi/L (pico-curies per liter of air), the readings ranged from 1.0 to a peak of 8.1. Any short-term test result can be a little higher or lower than a long-term test average.

• Test Location - A radon test should be performed in the lowest living level of a home, since that is where the radon concentration is likely to be higher. But radon can vary from room to room on the same level, because the gas coming up through any openings under the home can vary. Sometimes testing in multiple rooms finds a “hot spot” in a particular room.

• Age Of The House - Although a radon test is required to be a “closed house test" with all the windows and doors closed and exhaust fans off, all homes have a certain amount of air leakage, which is rated in air exchanges per hour. Older homes replace the total volume of air one to two times per hour, while newer home that are code-required to be more tightly sealed exchange only about half their air per hour. Since elevated radon in a house is based on an accumulation of the gas in a closed space, the “tighter” new construction will retain the radon gas longer.

• Cheating - Opening doors and windows or moving the test equipment outside will lower the radon level read-out, but it will also void the test if modern electronic equipment is used. New test equipment recognizes openings and closings of the doors and windows, changes in temperature and barometric pressure, and movement of the machine.

    If you are selling a house and the buyer’s radon test exceeded the EPA’s acceptable max of under 4.0 pCi/L, and you feel the test was not a good sample and want it run again, you do have that option. Usually the seller must pay for the second test, it must be done by a licensed radon tester, and the two test results are required to be averaged to get a new number. However, if your initial test result is much more than 4.5 pCi/L, the possiblity of an average coming down to below 4.0 is slim.

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Here’s links to a collection of our blog posts about “RADON":

• Is a radon mitigation fan required to be on a dedicated circuit breaker/fuse in the electric panel?

• What happens to a radon test result if the windows were opened, the test device moved, or there was any other evidence of tampering during the test? 

• Where do I find the Florida laws regarding radon?

• Can I test vacant land for radon before building a house? 

• Is radon mitigation possible for a condominium?

• Do radon mitigation systems require maintenance?

• What is the average life expectancy of a radon mitigation system?  

• Do older houses have higher radon levels than new houses? 

• Can the seller tamper with a homebuyer's radon test to change the results?

• How long does it take to get the results of a radon test? 

• Will opening the windows reduce the radon level in a house?

• How was it determined that between 15,000 and 22,000 lung cancer deaths each year are caused by radon?

• Can a homebuyer do their own radon test for a real estate transaction with a self-test kit?

• What is the danger of radon in well water?

• What are the symptoms of radon poisoning? 

• Does Florida have radon?

• Where does radon come from? 

• For how many years does an old radon test result remain valid?

• Should homeowners get a pre-listing radon test before selling their home?

• What are a homebuyer's options when the radon test comes back high (4.0 pico-curies/liter or more)? 

• Do granite countertops emit radon?

• How can I tell if a house has a radon mitigation system? 

• Can a mobile/manufactured home have a high radon problem?

• Do I need to test for radon when buying a condominium? 

• What does a radon mitigation contractor do to lower the radon level in a home?

• How can not testing for radon be an expensive mistake for homebuyers? 

• Will the radon test come back sky-high in a house that has been empty and closed-up for months? 

• What is radon? Should I be concerned about it?

• Should I buy a house with a high radon level? 

• What is the average radon level of indoor and outdoor air in America?

• What is the operating cost of a radon mitigation system? 

• Should I buy a house with a radon mitigation system?

• Does the buyer or seller of a home pay for radon mitigation when the radon test comes back high? 

• What is the probability of having high radon in a Florida house?

• How quickly do I need to reduce a high radon level in my house? 

• Does a home inspector check for radon?

• What are the problems with underground return air ducts? 

    Visit our RADON page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.