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Thread: cfm for ac

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  1. #1
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    cfm for ac

    about a year ago i had a goodman furnace 70,000 btu and heatpump 3 ton put in. they set the cfm to high 1449 cfm. is that to high? medium is 1192. i know from being on this sit it should be about 400 cfm per ton. i have about a 21 degree drop at the a coil. is there something i dont understand? should it be at 1449cfm or should i call someone out to to look at it and set it to 1192 if need be? my furnace is GMH95 0703BXA and here is a link for the cfm http://www.goodmanmfg.com/Portals/0/pdf/SS-GMH95.pdf thank you chris

  2. #2
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    Yes for a heat pump 400 CFM per rated nominal ton is correct, and a 21 degree drop is also good sounds like your running ok. I would not worry about it every manufature has it's own specifications

  3. #3
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    Quote Originally Posted by Tiger93rsl View Post
    Yes for a heat pump 400 CFM per rated nominal ton is correct, and a 21 degree drop is also good sounds like your running ok. I would not worry about it every manufature has it's own specifications
    do you think i could have it turned down so it is not so loud? i sit right next to the intake and the furnace is right on the other side of the wall. if i could have it turned down it would be great but i dont want to call someone out and have them say it is were it need to be and pay a service call for nothing.

  4. #4
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    I would like to see it set at 1192 if it were mine. Does your coil have a txv?

  5. #5
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    Take note that the fan data you posted,shows cfms at various ESP(External Static Pressures),so wihout testing the ESP,there's a wide range of cfms,depending on the ESP(think resistance to air flow,of ducts,filter,etc.).


    Based on the temperature drop,I'd guess your cfns cold be on the low side,or within proper range.Get a Pro that can test ESP and set the correct speed.


    Read here for an option to reduce noise; http://www.hvac-talk.com/vbb/showthread.php?t=176333

  6. #6
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    I doubt your getting the 1449 CFM with a 21°F temp diference on a 3 ton unit.

    Its a year old now. Time for a service check anyway. Have them check and adjust blower speed if needed.
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  7. #7
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    Supposedly, they like to use 450-cfm per/ton, on heat pumps. That would be 1350-cfm for a 3-ton HP.

    It is not delivering 1449-cfm or 483-cfm per/ton, as stated; 21-TD indicates being on the low CFM side, unless you have a low indoor humidity factor.

  8. #8
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    Quote Originally Posted by beenthere View Post
    I doubt your getting the 1449 CFM with a 21F temp diference on a 3 ton unit.

    Its a year old now. Time for a service check anyway. Have them check and adjust blower speed if needed.
    is a 21F temp drop what it should be?

  9. #9
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    Goodman has a listing of temp differences at different CFMs.
    But you need both the outdoor unit and indoor coil model number.

    My guess, is your moving around 1050 to 1100 CFM.

    Your duct system may be too restrictive for your blower to move the 1449 set CFM.
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  10. #10
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    Quote Originally Posted by aintitfun View Post
    I Does your coil have a txv?
    yes

  11. #11
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    Feb 2008
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    if you return is to loud from being to short. have a company line you return can with acustical insulation, it will reduce the noise by at least 30%.it only takes about a hour or two of labor and the material is cheap

  12. #12
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    Quote Originally Posted by furnacemaninc View Post
    if you return is to loud from being to short. have a company line you return can with acustical insulation, it will reduce the noise by at least 30%.it only takes about a hour or two of labor and the material is cheap
    they put what looks like bubble wrap with aluminum foil on both sides of it on the inside of it. the intake is only about 6 inches long

  13. #13
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    boy i love lack of return air and excessive fpm across filter grill

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