Most new houses in the U.S. are built with central forced-air systems for heating and/or cooling (HAC). Devising methods to minimize or eliminate the negative impact of the residential HAC system on soil gas entry is crucial to constructing houses with good indoor air quality. Soil gas can contain a number of unhealthy contaminants, such as radon, volatile organic compounds (VOCs), pesticides, and biocontaminants. The poorly planned and installed HAC system can induce pressure differentials that drive the entry of soil gas into a building. The faulty HAC system also distributes the contaminated air to the living space. Conversely, a properly planned and installed HAC system can reduce soil gas entry, dilute any soil gas that enters a house, and increase ventilation rates to improve overall indoor air quality. The paper describes some recommended and proven techniques for HAC configurations that have lowered the entry rate of radon in new construction, and which could be applied to reduce the entry of other soil gas contaminants.