My air handler is in the master bedroom closet 4 feet from the bed and I'd like to enclose it as much as possible with some sort of sound proofing. We prefer to not have a closet door which would help, of course (it's a long story). The intake is through the wall to the hallway, so I don't think enclosing the unit would be a problem. Any advice?
Close it up as tight as you want, just make sure you have some form of access in order to do maintinence on the unit. You don't really need any clearances on an air handler other than for servicing. Insulate the crap out of the closet and close it up.
to block sound, think MASS! & isolation.
read about audio room sound deadning --
ie: build a second 0.625" thick drywall seperated from the existing wall with steel drywall bars to be springy --
stuffing the existing wall with insulation will help slightly, but the existing wood studs & gyp vibrate --
one can buy lead loaded sheets = ACOUSTIBLOK.com