An investigation of unbalanced forced-air heating systems in historic homes and the potential for resultant moisture problems in the building envelope

Unblanced forced-air heating systems create a situation that may be detrimental to the building envelope. These systems create an air pressure differential, which acts as a moisture transport mechanism, which has the potential to carry moisture, through the smallest of openings in the building envelope. Once this warm air enters the wall cavity it comes into contact with the unheated surfaces of the components making up the building envelope, which are below dew point during the heating months. As this moisture-laden air reaches its dew point, condensation occurs.