AVS Special Member
Join Date: Dec 2008
Location: L.A. - Lower Alabama
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I'm having a little trouble following exactly where things are going. A layout would be nice. However, if I understand correctly, you are referring to the AC compressor (outside unit) that is next to the exterior wall of your theater and a "furnace" that will be in the garage. When you say furnace, are you talking about the air handler? Is it a heat pump / furnace combo? i'm not sure where you live, so I don't know the climate.
As far as the exterior unit goes, our house is brick veneer, OSB decking, 2x4 walls, spray foam insulation, standard double pane windows, and 1/2" sheetrock on the inside. We have a 5 ton Trane unit just outside our dining room (which has windows on 3 walls, and I can barely hear it when it kicks on. I may not notice it at all if it wasn't for hearing the thermostat click and seeing the slight dimming of our lights. Generally, these newer AC compressors are fairly quiet as the trend has been to make the units larger and more efficient (larger slower moving fan) that has made them quieter. The moral of all that is I don't think I would worry too much about the AC. You'll have your exterior finish, fiberglass batts (I'm assuming), decoupled walls, and DD+GG to help limit with the noise intrusion. You might ask they they pour the compressor pad with a gap between the house and the pad just limit the noise coupled into the foundation, although that may have little to no impact.
Will the furnace be in it's own room, or will it be open to the garage? If it's in it's own room, you could consider clips+channel+DD+GG in there. Also, if it's not, you might just see if you have any noise issues, and if you do find it objectionable, you could build a room around it and use clips+channel+DD+GG. That way you don't waste money fixing a problem that may not exist. Our variable speed air handler is directly above our bedroom, and I can hear the wind noise from the return and vents, but I don't notice the sound of the actual air handler.
Did John discuss using IB-1 clips rather than whisper clips? Just something you might want to ask about. Dennis doesn't spec them, but it's good to know your options.
As far as screws, I used the Grip-Rite exterior coated screws. If I had it to do over again, I would use 2" screws exclusively, as their 1-5/8" screws are smaller, even though both the 2" and 1-5/8" screws are both supposed to be #8s. The SIM for the particular whisper clip you have will specify which type and size screws to use.