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Condensation in Attic HVAC System
Trying to determine the best solution of this problem. My house has 2 HVAC units, one in the basement and one in the attic. The basement HVAC unit mostly heats the 2 story home as it has a 2 story foyer and family room and being so open the basement unit provides the heat for both stories. We use set back thermostats and the attic HVAC system almost never comes on in the winter for heat as the basement unit maintains the thermostat settings of both systems.
The attic HVAC system and ductwork has been sealed and insulated but during the winter months as the warm air migrates into the attic ductwork, furnace and A/C coil, in time condensation forms inside the ductwork and unit.
Considering that the unit almost never runs in the winter in time the system and ductwork temperature will match the attic temperature even though they are well insulated.
So thoughts are maybe put a strip electrical heater in the HVAC unit and cycle it on a thermostat, considered putting a return air damper that would close when the unit is off but unless 100% air tight, I don't think this would work.
Also as I have some access from the basement to the attic maybe run small diameter duct from the basement unit to attic HVAC unit to provide heat into that unit.
If I would have thought of it, I would have put thermal traps in at every diffuser and return air in the attic HVAC system and most likely would not have this problem.
Also if I ever build another home, I will installed sheets of insulated foam sheets on the 2nd floor ceiling before the drywall ceiling as it would have a much better insulting effect than insulating the attic. They do this on the exterior of the home but I have never seen it done to the 2nd floor ceiling even though it would be the same principal.