Condensation from the differential temperature is of course on answer. The other and more concerning is the furnace or force air unit (FAU). I would recommend contacting a licenced heating contracto ... read more
http://www.ncsg.org/ The National Chimney Sweep Quild is a great source for licenced and certified professionals in your area. If they don't do the work, they will know someone in your area who does. ... read more