Posted By tkhayes on 02 Jun 2010 11:15 AM
I live in Florida. Our house, built 1970's, has a smallish closet next to carport at the corner of the house that contains the HVAC and air handler.
The room that it is all in is not insulated, nor does it appear to be an efficient path to push air some 70' to the other end of the house.
I am getting ready to put a newer high efficiency unit in the house. Am thinking of moving it all to the attic, which has a fair bit of room. I can build a platform to put it on, install the proper drains, etc., and have a shorter return air path.
Shorter path for return and cold air ducting, but the attic is not insulated itself, but I also have R40 up there for the ceiling.
Will I see a gain in efficiency, or simply lose more because it is 140 degrees up there in the summertime?
any ideas?
thanks
To keep from losing efficiency you can:
1: seal & insulate (to at least R10) the ducts & air handler
2: put radiant barrier between the hot roof deck and the ducts & A.H.
It's better to have it all fully within conditioned space, but it's possible to do OK even in hot attics with enough insulation. Air-sealing the ducts & air handler is critical to minimize the losses from being outside the pressure boundary of the conditioned space. It's important on two levels- leakage induces outdoor air infiltraition into conditioned space by creating a pressure differential, and it just plain throws away a fraction of the already cooled dried air.
The insulation also needs to be air-tight to keep humid attic air from getting in and condensing on the ducts. 1.5-2" of closed-cell spray foam takes care of both sealing & insulating on the ducts, but on the air handler you might want to go with rigid foam board cut to fit, with FSK taped seams & edges (so it can be serviced more readily if need be.) Foil-faced foam board (1.5-2" polyisocyanurate) would be best, since it would absorb less radiated heat. Radiant barrier at the roof deck keeps the surface temp of the duct insulation at the attic-ambient rather than absorbing radiated heat & rising above the attic air temp.