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  1. #1
    Join Date
    Aug 2009
    Location
    Georgia
    Posts
    2

    Heating and cooling for finished attic space

    I live just west of Atlanta Georgia and in the process of finshing approx. 750 sqare feet of attic space. It is basically two rooms. One is over the garage and the other is over heated and cooled space. I plan on putting a lot of care and money to make sure it is insulated properly to make it as air tight as possible. I just got my first estimate today. The gentleman was referred by a friend of mine and has many years in the business. He walked me through the plan and explained everything to me. He told me that the room over the garage was going to need the most air due to the unfinished garage and the heat of the roof. He quoted me a price for a 2.5 ton unit. I spoke with another professional about the tonage and he thought that was to big seeing that it is 1 ton per 300square feet. The gentleman that quoted me the job also told me that he is not a big fan of flexible duct work and always builds is on rigid duct work. Does this sound like an over kill on the tonage or is it about right. He also quoted two prices. The first one with a 13 seer rating and the next with a 14 seer rating. The 14 seer rating was 1000 dollars more and came with a variable fan handler. Any suggestions. I will be getting more quotes. I need to know if a contractor quotes me a 1.5 ton than I don't need to use him. Thanks for you advice.

  2. #2
    Join Date
    Jul 2009
    Location
    Houston,Tx via Wilmington,NC
    Posts
    59
    Sounds a little high to me but he might see something I can't see. Do a load calculation on it and go from there.

  3. #3
    Join Date
    Jul 2009
    Location
    Houston,Tx via Wilmington,NC
    Posts
    59
    You can get homeowners HVAC Calc for $49.00

  4. #4
    Join Date
    Aug 2009
    Location
    Georgia
    Posts
    2

    Thanks

    Thank you for your reply. When figuring out the tonage with 9 foot ceilings, how many tons per square feet. I have seen some charts that say 1.5tons per 600 to 700 sqare feet in the region of the country I live in. Is this about right?

  5. #5
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,907
    There is never a time when tons per sq ft is correct. That's why the only right way to size is with a heat gain study like the Manual J.

    We have a floor plan very common in the older section of our suburb. In replacing equipment in these homes, we've used, 2, 2.5 and 3 ton equipment. Same sq ft, same house. All sized correctly.

  6. #6
    Join Date
    Jul 2009
    Location
    Houston,Tx via Wilmington,NC
    Posts
    59
    Thumbs are good for alot of things,sizing A/C's is not one of them. Rule of Thumb does not work.

  7. #7
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    17,904
    When you are talking with contractors regarding tonnage, the size recommended should always be dictated by a load calculation.

    And, efficiency costs money.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

    AOP Forum Rules:







  8. #8
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,139
    there have been several threads about heating and cooling bonus/attic/garage rooms..

    usually hvac is oversized due to high heat gain in these areas located within
    hot attic

    insulating and air sealing the walls is the key
    what you have is simply put a box surrounded on all sides by attic temps
    if it is 100 degrees outside by mid afternoon the attic is 130 degrees
    attic walls that are shared with living space walls should be insulated
    better than exterior walls...but it just doesn't happen in the real world.

    if you first insulate these walls then seal them for air tightness it will
    change the dynamics of the space to be heated and cooled.
    its all about air and thermal boundries.

    once these improvements are made it will be much more affordable to heat
    and cool this space. 300 sq ft is out the box...fix the space..then buy
    correctly sized hvac.
    oversizing will cost you in higher tons to buy, operate and will not allow
    for proper dehumidification.

    efficiency does cost money..and upfront money. but it is an investment that
    pays back long term when done correctly.

    best of luck.

    southface institute has good information on air sealing.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

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