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  1. #1
    Join Date
    Feb 2010
    Posts
    3

    Default 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.

  2. #2
    Join Date
    Feb 2010
    Location
    Iowa, Quad-Cities area
    Posts
    129

    Default Re: Central A/C in attic

    The unit can be installed horizonally or vertically, depending on the room. Can you designate (or sacrifice) some room on the second floor for the air handler or does it have to go in the attic? Why do you want to zone the system? Is the area that large? Don't get me wrong, I love to zone but it's not always necessary. You can go with one return but you should have tranfer grilles to the rooms that can be closed. That said, you need to design the return to reduce the air noise. What will be the area that you're cooling?

  3. #3
    Join Date
    Aug 2007
    Location
    The Great White North
    Posts
    4,045

    Default Re: Central A/C in attic

    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.
    Well that's definately something you need to consider.
    If you don't want climb into attic perhaps the kids should be sent up.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  4. #4
    Join Date
    Feb 2010
    Location
    Iowa, Quad-Cities area
    Posts
    129

    Default Re: Central A/C in attic

    Quote Originally Posted by lsag02 View Post
    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.
    To answer your question on getting to the filter, if the air handler is located in the attic, then one option (so that you don't have to crawl into the attic) is to have a central "filter grille" or two (depending on the A/C size requirements). Sizing for a filter grille should be 2 cfm per squire inch; i.e 16x25 = 400 x 2 = 800 cfm (2 ton).

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