Central A/C in attic


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 appreciated.
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 filter.
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.
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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.
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On Feb 17, 9:47 am, snipped-for-privacy@webtv.net (Lp1331 1p1331) wrote:

So there is only one main return as I do not see how otherwise you can provide additional returns from the rooms.
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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
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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 blocks.
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.
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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.
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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.
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Colbyt wrote:

Easy there sharp shooter, he said he doesn't know how these systems work but wants to learn. I guess you aren't the teaching type?
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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 air

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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 efficiency.
--

Roger Shoaf

About the time I had mastered getting the toothpaste back in the tube, then
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ls02 wrote:

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.
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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 greatest isolation. 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.... goodgawd....
--
EA


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Existential Angst wrote:

50 pair, $6.99. http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber–365
Probably dishwasher safe...
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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 to fit. 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.
--
EA




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So, do you set the unit on them to reduce vibration? :-)
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wrote:

You can do either. Since this is in the attic install a large tray under the condensor unit with an overflow line to the outside. Get a $10 water alarm. Blowers are typically quiet.

The filter may be installed in the main return or near the unit, whichever is most convenient for changing/cleaning the filter monthly.

At least one vent in every room. Usually one return.

No. But, you can put additional insulation on oe over the ductwork.
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