It can be done, suspension and vibration isolators could make it an unnoticable unit however, given all the other concerns, I wouldn't do it.

It is not a desirable location, but the only one available in some houses (slab, retrofit).

The easiest way to minimize any vibration is to hang the unit from a couple rafters using chains, then put vibration isolators under the unit in the backup drain pan.

If the rafter span is large or the unit heavy you may need to sister up the rafters and add blocking to keep them from twisting.

Very interesting. Thanks to you both. It's not for me, but rather a person I met and was confused about it.

Thanks again and I'll pass this info on.

I guess the room below it will have some noise issues no matter how much insulation is boxed around it.

ES

every home around here has the airhandler/furnace in the attic. my house has 2 HVAC systems so i have one at each end. they are hung by chains from the roof supports. there is no vibration even without any other isolators. due to our flat land and high water table no one here has basements and only homes built within hte last couple year have them in a closet somewhere, and this is because for some reason the newest homes built here seem to have almost no attic space.

D&K, to clarify:
This is about normally outdoor condensers mounted in attics

Evans,

There are ducted condensors, but are getting rarer and more expensive every day.

"for some reason the newest homes built here seem to have almost no attic space."

Truss roof construction, be glad yours isn't as time will tell, besides being a firemans nightmare.

Firemen won't bother going interior which usually requires going on roof to ventilate, if fire makes it to attic, hope your family got out.

wait, i misread that, i have never seen the outdoor unit installed inside! to me that seems like it would add a lot of heat to the attic during summer plus place undue stress on the compressor.

It certainly can. In one case I saw a unit with an interlocked exhaust fan to expel the heat from the attic, which certainly adds to operation cost.

Given no choices though, like a row house with no access, it can work.