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  1. #1
    Join Date
    Sep 2009
    Posts
    2

    Default Air conditioning not efficient

    I have a 2400 square foot rancher with 9' high ceilings. In the great room/kitchen and breakfast area I have 13.5' high cathedral ceilings. The house is 5 years old and has 2 gable vents at each end of the house, vented soffit and 3 vents in front of the house. When the temperature goes above 85 degrees I can not cool the house below 78 degrees and the central air runs all day. Which solution would help my air conditioner be more efficient?
    1. Ridge venting
    2. Roof mount power vent.
    3. Ehaust fan at gable vent
    Also would any of these qualify for energy efficient tax credits?
    Do you have any other suggestion that would help to cool my house more efficiently?
    I live in Pa.
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    Last edited by robbypm; 09-09-2009 at 03:08 PM.

  2. #2
    Join Date
    Jul 2009
    Location
    Northeast
    Posts
    661

    Default Re: Air conditioning not efficient

    There's a few things that I'd check if I were you.

    1. Has your A/C System been properly sized, it sounds like it's undersized as you say it runs all the time.
    2. Is the Duct work Taped Sealed and Insulated? If not the cool air will pick up heat and your supply air will not be as cool as it should, 60-64 degrees is a good supply temp.
    3. Do you have enough Returns and are they pulling back as much air as is being supplied and, are they on the floor or in the ceiling? You have some pretty high ceilings and if the Returns are down low the hot air will get trapped high, (heat rises).
    4. Does your Condenser have the correct Ref. charge?
    5. What is your Temp. drop across your coil? It should be 15-20 degrees.

    If your attic is properly insulated I doubt the reason your house is not cooling would be the venting. A/C Units are sized in tonnage, a heat load calculation would tell you the exact size you need, sq. footage, window type, door type, Ins, etc.
    1 ton = 400 cfm so a rough guestimate would put you in the 6 ton area but with out a Manual J (load calc) you will not know the size that your house needs, all HVAC Contractors should do this. If you talk to one that does not, move on to the next one and get a copy of Load Calculation. Good Luck!!!

  3. #3
    Join Date
    Sep 2009
    Posts
    2

    Smile Re: Air conditioning not efficient

    Sten,

    Thank you very much for your very informative information. After reading your reply I'm pretty sure you hit the nail on the head. I just assumed that the contractor sized the A/C unit properly and thought that more ventilation was needed in the attic. I do have taped duck work that is insulated and most returns are in the ceiling, however I not sure if there are enough outlets to cool the house. I will be contacting a HVAC contractor that can analyze my system and one that can perform a Manual J load test as you suggested to determine if my A/C is properly sized.


    Thanks again for the info.

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

    Default Re: Air conditioning not efficient

    Your A/C should be a 4 ton. Check the plate on the condenser.

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