Thread: Winter Months Increase Radon Danger - Consumer Affairs

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Winter Months Increase Radon Danger
Consumer Affairs - 1 hour ago
With 99% of the loan process complete, the home inspection showed a radon level above the state standard," Joseph told consumeraffairs.com. ...



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• Experts advise homeowners to give house a post-winter checkup - Ann Arbor News

That was a very informative article although it may have over-simplified the reasons radon levels tend to be higher during winter months. People usually keep their doors and windows closed more during the winter so the air (and radon) inside the house is less diluted than during warm months.

Another component in higher winter radon levels is stack effect. With cold outside temperatures and warm indoor temperatures the warm air inside the house rises and some of it finds its way into the attic. (The greater the differential between inside and outside temperatures the greater the amount of stack effect.) When the furnace is operating the exhaust gasses are vented up the chimney. This air that leaves the house (exfiltrating into the attic or venting out the chimney) lowers the pressure in the house and draws air into the house to replace that lost air. Some of the air drawn into the house is soil gas (including radon) drawn in through cracks and voids in the foundation.

So, not only is the inside air typically less diluted during winter months, more radon is being drawn into the house.

AARST (American Association of Radon Scientists And Technologists) had an interesting article in their Fall 2007 issue of Radon Reporter - Seasonal Variations Found To Be Significant in Alabama Study - about the results of a study by The Alabama Radon Program. Several homes in Alabama that tested below 4.0 pCi/L during the summer were retested during the winter. The study found that winter tests were above 4.0 pCi/L in 41% of those homes. In 20% of those homes the radon measured above 8.0 pCi/L and 10% had radon levels above 20.0 pCi/L. This may come as a surprise to homeowners who bought their home (and did a radon test) in the summer and sell their home (and the buyers does a radon test) in the winter.

The evidence seems to indicate the longer the heating season the greater the variation between summertime and wintertime radon tests. The group in Alabama is conducting more tests to get a better handle on this.

My experience has been somewhat different. In a one-year study of a house doing a series of 2-day radon tests I have found that some of the highest radon levels were measured when the weather was the hottest and during windy conditions. During mild conditions the radon levels tended to be lower. I attribute the high radon levels during hot weather to stack effect - the air in the attic gets hotter than normal and more air vents out of the attic drawing more air from the house and, in turn, drawing more radon into the basement. During windy conditions I suspect the wind is creating a negative pressure in the house (much like wind blowing across an airplane wing creates lift) which draws more radon into the basement. Conversely, on some very windy days the radon levels were low; perhaps the wind was pressurizing the house.

My study is not complete and will run through the winter. That will give me one year's worth of data - a series of 2-day tests, 1-month tests, 3-month tests and a 1-year test. All these tests are in the same location in the same house. So far the extremes are 5.6 (October - very windy) and 20.9 (August - thunderstorms).

What is important to understand is that a short-term radon test, no matter how accurately the radon concentration is measured, is only a snapshot of the constantly-changing radon levels of a home. As EPA has stated all along a long-term test provides a more accurate measurement of the yearly average radon concentration.

It's a shame the guy in Brian's article cancelled his home purchase because of a high short-term radon test. The home inpector who performed his radon test should have explained to him that almost any house can be "fixed" (mitigated) to reduce the radon levels in the home to well below 4.0 pCi/L. Plus, if he could have done a long-term test, it is possible, even likely, the long-term test results would be lower than his short-term test results (unless his short-term test was performed during a very high period).