Size of HeatPump
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  1. #1
    Join Date
    Nov 2005
    Posts
    4
    In our upstairs, we have 960 sq ft consisting of 4bed 2 baths. We will have 1 heat pump to service this area. My contractor is pushing me to get:
    * 3 Ton variable speed air handler
    * 2.5 Ton Heat pump

    Isn't that to big? What are the advantages & disadvantages to putting in an oversized unit? Will I be blown out by rushing air when the system is on? Will I spend more $ on electric costs?

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,819
    Only a load calc will tell you if it is too big. Sounds like it to me but depends upon location, windows, insulation, etc. Before putting 2.5 tons on that small of a space, demand to see how he arrived at that calculation and get assurances that your ducts can handle that kind of airflow.

  3. #3
    Join Date
    Nov 2005
    Location
    USA
    Posts
    529
    Isn't that to big? It sounds too big but only a load calc can tell.


    What are the advantages & disadvantages to putting in an oversized unit? Advantages=0, Disadvantages= uncomfortable air, mold problems, and possible compressor failures.

    Will I be blown out by rushing air when the system is on?
    This is a result of the ductwork design and system cfm, not tonnage.

    Will I spend more $ on electric costs? No, however it will not be comfortable if sized improperly.

    Get a load calc professionally done.
    The posts and comments made by me are in no way affiliated with any company or organization. They are simply my personal opinions.

  4. #4
    Join Date
    Mar 2004
    Posts
    1,042
    I agree with the above, except for one point- an oversized system will cost more in utility bills. These systems take several minutes of running before they can reach any meaningful level of efficiency, and oversized systems rarely get to run long enough continuously to get to the efficient stage.

    The lack of comfort produced by an oversized system (inadequate dehumidification) typically leads people to set the thermostat to lower temperatures than they would otherwise, which pushes the utility bills higher still.

  5. #5
    Join Date
    Oct 2005
    Posts
    922

    Cool Design manual / Load

    Big /Way over sized = Will short cycle on off on off on off?

    Think of as putting a jet engine in a small VW bug and just going to the store for milk or the paper every day.

    Over sized a little too much = will short cycle, bump on off?

    Think of driving a tractor trailer to get milk or the paper every day.

    Sized just right = energy efficient no short cycle, runs on the maximum time and shuts down for the maximum time.

    Think of driving to get the milk and paper in the VW bug

  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,595
    Here in Lanc, PA, that would be grossly over sized.

    Where are you located?
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  7. #7
    Join Date
    Feb 2005
    Location
    Dothan, Al
    Posts
    3,453

    Condor

    If yur in the south, it is not too big.
    What yur contractor is telling you is that he recommends a 2.5 ton system with an oversized indoor coil ( 3 ton size )
    With 960 sq ft, rule of thumb would be 2 ton, but an upstairs area generally gets warmer du to the warmer air from downstairs rising to the upstairs, so the upstairs will have more heat to 'condition'. I. personally don't like the idea of the larger indoor coil,( I know it is suppose to make the system more efficient ) but I have never installed one either. I would prfer to go with the 2.5 indoor coil for the humidity removal, if nothing else.Either way, if in the south, I wouldn't go any less than 2.5 ton - to insure comfort.

    Hope this helps,
    Richard

  8. #8
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,513
    i agree with Born on this. Only need add is do a load calculation

  9. #9
    Join Date
    Nov 2005
    Posts
    4
    Thanks for all the replies! We live in Atlanta and we do have a wide stairway so we get a lot of air moving up and down the stairs.


  10. #10
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,595
    Have your contractor do a load calc, or do your own, by clicking the hvac calc tab at the top.

    If 2.5 tons is over sized, you'll have alot of humidity trouble.
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