Extemely high test results, like the one shown above, do happen occasionally; but they are not the result of a closed-up house.The test results will not vary significantly from what they would be in an occupied home. There are several reasons for this:

1.  Radon has a half-life of just under 4 days. This means that the radon that entered the home a month ago will now be approximately 1/250th as radioactive as it was, and decreases to virtually nil shortly thereafter. It doesn’t keep accumulating.
2.  No house, even a closed-up one, is airtight. All the cracks, crevices, loose caulking, and gaps around doors and ceiling penetrations add up to the equivalent of a hole in the wall of an average house. Plus, houses have a natural suction, called a “stack effect,” that pulls outside air in and up through the roof. Slow, but regular air changes occur even in a closed house. 
3.  Most of America lives with their windows closed today, and a recirculating heating/cooling system. So a closed, empty house is not all that different from an occupied one.

   The protocol for radon testing in a real estate transaction calls for the house to be closed for at least 12 hours before the beginning of the 48-hour test, and remain closed for the duration, in order for the test to simulate the living conditions of the average home. 

    For more information about radon we recommend that you visit the U.S. Environmental Protection Agency’s radon homepage at http://www.epa.gov/radon/. Also, you can click on any of the three report covers below to download consumer guides to radon from the EPA.

    Not sure whether testing for radon is worth the cost? Before you decide, read our blog post How can not testing for radon be an expensive mistake for homebuyers?

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

• Is a radon test required to sell a house? 

• 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?

• 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? 

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

• What factors can change radon test levels up or down?

    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.