*If the unit is the type that I am thinking of you should have two PVC
pipes coming off of it. One is for fresh air and the other is exhaust.
The exhaust pipe must be pitched (Sloped downwards slightly) towards the
outside so that condensation will drain outside and not into the unit.
Check to see if that is so. Also if your unit is not pulling air in
directly from the outside it would be a good idea to bring fresh air into
the room.

On a typical condensing furnace, the PVC vent piping will slope slightly
UPWARD toward the outside,
so that the condensate in the vent will drain back thru the furnace
condensate handling system. See page 14 of the
installation instructions here for a typical system:
http://icpindexing.mqgroup.com/docum...4001105007.pdf
8. All exhaust vent piping from the furnace to termination

MUST slope upwards. A minimum of 1/4? per foot (6.4mm

per 304.8 mm) of run is required to properly return

condensate to the furnace drain system



*OOPS. You're right. I shouldn't respond to these things before coffee.