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Hidden ducts fan radon threat.

Some homes without basements contain duct systems embedded in the walls and beneath the first floor to facilitate the fan-driven circulation of air to furnaces and air conditioners. Because these "underground air returns" tend to be quieter, more efficient and less visible than standard air ducts, they have become popular in several areas of the United States. But many of these systems - especially concrete ones - may suck large amounts of radon from the soil because they were not well sealed during construction, observes Kimberlee J. Kearfott of the Georgia Institute of Technology in Atlanta. Her study of eight homes in Phoenix, Ariz., demonstrates that such underground returns can increase indoor radon concentrations by "10-fold or greater," she reports.

Kearfott collaborated with Arizona-based colleagues who monitored radon in each home, as well as outdoor temperature, air pressure, humidity and precipitation, for two weeks during the summer. Each home showed a clear diurnal variation in radon. "The only thing these variations correlated with was usage of the cooling system-in other words, when the underground returns were in use," Kearfott says.

Though many residents leave their cooling system fan running even when the air conditioner's compressor shuts down, this may not be wise, at least in some homes studied by Kearfott's group. For instance, radon levels in one home fell 35 percent when the occupants switched the fan from running continuously to running only when the thermostat called for it. If indoor radon levels prove worrisome - well above EPA's 4-picocuries-per-liter action limit - Kearfott recommends considering a more drastic measure: lining the ducts with a gasimpermeable sleeve.
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Title Annotation:duct systems can increase radon concentrations in the home
Author:Raloff, Janet
Publication:Science News
Date:Aug 3, 1991
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