I am planning to install central A/C in attic for the house addition
and three existing rooms on the second story. There will be no forced
air furnace, just central split system A/C.
I cannot find any good resources and particularly a diagram of
installing just central A/C in attic. Any advice or links would be
I understand the unit is installed in horizontal position. Should it
be installed on ceiling joists or hung from roof rafters? The unit
will be directly over the bedroom so I worry much about the noise. Is
anything I can do to make it run quite and reduce vibrations?
How does the air filter get changed when the unit is in the attic? I
obviously do not want to climb to the attic every three week to clean
The unit will have two zones and will supply air to 7 rooms of
different sizes. I will hire a pro to do a design and load and heat
loss calculations but I still want to understand it myself. Should I
have just one main return or return from every room or both main
return and return from every room?
I understand that ducts in attic must be well insulated. But should I
also insulate entire unit? I guess it does not need combustion or any
other air and I can build a box around it from Styrofoam sheets.
Units are installed either way-- hung from rafters or on the joists. It
would probably be slightly quieter hung from the rafters. The most
important thing is to get enough slope on the condenstate drain line,
and make sure the secondary drain pan is istallled under the unit
properly. The unit does not need any extra insulation, but obviously the
ducts must be properly insulated for efficiency and preventing
condensation. Usually filters are installed at the return air grille(s).
That way they can be serviced without going ino the attic, and also the
return duct will stay clean. Otherwise, a Space Guard or similar filter
can be installed at the unit, and only needs changing yearly-- maybe
even less depending on useage.
ls02, I'm not really sure what you are asking. If you use a SpaceGuard
or equiv. filter, it would usually be installed right at the unit and
then a box/plenum or a duct trunk line would go to the intake side of
the filter assy, and then however many return ducts you want could be
hooked up. You could put filter return grilles in every room if you
wanted, but servicing a bunch of filters every month or so could get to
be a PITA, as well as expensive if you use throwaway filters. The
smaller ones that would typically be used in applications like that
(often 12"x12") cost as much or more than larger ones.The more returns
you have, the more even the temperatures usually are, as well as
quieter. You are usually limited only by your budget, and the
accessbility in the attic. (you can't stuff 10lb of "stuff" into a 5lb
bag). HTH Larry
My attic unit, furnace and AC which is rated as zero-clearence at the sides
sits on it's side on a few small concrete blocks which are placed inside
the required water pan. First you need it that condensate overflow pan.
That pan must have a seperate drain from the regular condensate drain. Both
must go to a house drain or outside.
There may or may not be some rubber insulators between the unit and the
I have also seen them hung from rafters.
If you aren't smart enough to spend the extra bucks and buy a return air
grill that allows the filter to be installed on the living side. Then you
climb up there and change them once a month. A few extra bucks up front or
lifetime of misery.
That is best answered by the pro. It can be done both ways. I don't have
one in every room but I do have more than one. One larger one in a central
area and smaller feeded from the individual rooms that have one.
All duct work and plenum should be sealed and the insulated types used.
In your case with no combustion air required you might be able to improve on
the factory blower box insulation. Just keep in mind future service needs.
Make whatever you do removable.
Speaking of being smart enough, I always get a chuckle when guys
making these remarks do it while showing they can't even put a simple
sentence together correctly And that is the case in this example:
If you aren't smart enough to spend the extra bucks and buy a return
You might want to consider a slightly different option. They make units
where the condenser and the compressor are outside and inside each room you
want to cool has an independent evaporator and fan so you do not have
ductwork to run, just pipes to each evaporator unit. This costs a little
more than the package unit, but they are very efficient, so you get payoff
in energy consumption. It will also allow you to make 7 zones really easy
so you do not have to cool unused rooms as much so gain additional
About the time I had mastered getting the toothpaste back in the tube, then
Hanging from the rafters will transfer any vibration to the exterior walls.
Hanging from the rafters on sufficiently strong springs will dampen the
vibrations even more.
On the other hand, earplugs are only about fifty cents.
Yeah, but you can chafe yer ears, get ear infections.... :)
Attachment to any structural member is dicey.
And, you'd want to use the softest springs practical for the load, for the
And then, proly suspend those springs from nylon strapping, etc.
Vibration/noise isolation is quite the experimental art, and quite a low
priority amongst hvac companies.
In my kitchen hood disaster, I had to suspend the supports on styrofoam....
Ackshooly, proly not.
If they're foam, it's hard to imagine them being washable -- which
contra-indicates "disposable", at least in ear-plug jargon (I gotta watch
safety videos on this shit every year....).
HF likely mis-spoke (what else is new) on the washability issue.
In fact, yer only sposed to use these disposables *once* -- altho most
people use'em until they just get scuzzy...
You roll them in your fingers, slip them in the ear canal, and they expand
Rough on the ears, tho, esp. if you put them in and out often.
They DO, however, have one of the highest decibel ratings.
Much more comfortable and easier on the ear canal are the truly re-usable
rubber plugs, with the thin-ish flanges (one size fits all), with nearly as
high decibel ratings as the foam disposables.
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