[en] The level of radon and its daughters inside conventional buildings is often higher than the ambient background level. Interest in conserving energy is motivating home-owners and builders to reduce the rate of infiltration of fresh air into homes, and hence to increase the concentration of indoor air contaminants, including radon. It is unlikely, but possible, that the present radiation levels from radon daughters account for much of the lung cancer rate in non-smokers. In any event, it is likely that some increased lung cancer risk would result from increased radon exposures; hence, it is desirable not to allow radon concentrations to rise significantly. There are several ways to circumvent the increased risk without compromising energy conservation considerations