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Garalee 03-07-2011 09:35 PM

Hard Duct.
I am putting in a 2 ton Goodman split system heat pump and I would like to use hard duct in my attic. 1100 sf, 9ft ceilings,R-30 walls, R-40 ceiling, second story remodel. (Raleigh NC) An HVAC tech who is helping me is trying to talk me into using Flex. Hard duct just seems to be a higher quality to me. My attic will have foam insulation in the rafters, so it should be a conditioned space. His concern is during the summer, heat will still build up in the attic and cause condensation. If I have to insulate the hard duct I will just go ahead and use flex. Also, should I adjust the size of the unit because of the extra volume in the attic?

unicursalhex 03-08-2011 12:00 AM

consider the attic a conditioned space and insulate the duct accordingly. Hard duct is better but costs almost 2 times the amount

beenthere 03-08-2011 03:51 AM

If your foaming the rafters and the gable ends. then its a conditioned area, and a small 4" supply at one end and a small return at the other will take care of any risk of condensation with the trunk and supply lines. However, you may need to insulate the supply plenum, or first few feet on the trunk line. As this can still sweat since it can be 20 degrees colder then the surrounding air. Its more of a problem in homes that use set back in cooling mode.

Chris4mx 03-08-2011 08:46 AM

Put the hard duct in and have them spray it with the foam when they spray the rafters and gables.

Garalee 03-08-2011 03:41 PM

Thanks for the information, you have all been very helpfull!

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