Bane of the EPA

In 1990, the first of Bernard Cohen's studies was published showing that higher household radon levels were associated with lower lung cancer rates. The wealth of evidence rocked the scientific community, most of whom had never bothered to question the Linear-No-Threshold model. They were to be even further "rocked" by his even more comprehensive report in 1995. He is still [2005] evaluating even the most unlikely confounding possibilities that might discredit his highly significant findings. As a seeker of scientific truth, Cohen is working diligently to prove himself wrong.

The evidence chapters of this book contain many references to radon, including a whole chapter on Cohen's study (chapter 20). It might be a good idea for you to read them prior to spending big bucks for a government-approved, radon-reducing heat exchanger, which allowed circulation without appreciably changing the temperature of the room air.