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  1. #1

    Blower CFM and Coil Size

    We had a Lennox G60DFV-60C along with a 3 1/2 ton XP15 heat pump installed a few years ago. I have recently been thinking of installing an electronic air cleaner. While researching recomended blower CFM rates for EAC's I learned that my blower CFM should be set based on the tonnage of my heat pump (400 CFM per ton).

    I checked the current blower settings and found that it is set to 2068 CFM, which seems to be way to high. I would assume that it should be set to 1400 CFM based upon the tonnage of my heat pump.

    To confuse me even further, I also found that the coil that was installed is rated at 4.8 tons. Which may be the reason the blower is set to 2068 CFM.

    Ok, now to my questions.

    1) Is it "ok" that my coil tonnage (4.8 ton) differs from the tonnage of the heat pump (3.5 ton)?

    2) Should the CFM of my blower be set based on the tonnage of the heat pump or the coil?


    Thanks in advance for your answers.

  2. #2
    Join Date
    May 2002
    Location
    Houston Texas
    Posts
    6,316
    CFM per ton depends on your geographic location, a very fry air area needs more CFM a very humid location less air. A larger coil will be better for SEER/HSPF but will reduce humidity removal capacity.

    Your system may be setup well for your location it may not be, tell us where you live.

  3. #3
    Join Date
    Jun 2005
    Location
    The Gray Northwest
    Posts
    661
    Even though the blower dip switch is set at 2068, you may not be getting that amount of air depening on duct sizing and losses. Whomever installed your system may have tested ESP and set the cfm accordingly.

  4. #4
    I live in the Seattle area. I don't believe the ESP was checked when the system was installed (I was there for the installation). All the dip switch settings are the factory settings.

  5. #5
    Join Date
    Feb 2003
    Location
    garland, texas
    Posts
    663
    coil model number?

  6. #6
    Join Date
    Jul 2008
    Location
    RTP North Carolina
    Posts
    81
    Without knowing your ESP, there is no way to tell you what your true CFM is. Just because your fan is rated at 2068 CFM when set to high, does not mean thats the amount of air your fan is actually moving. So if you're reasonably sure that the ESP was not measured when the unit was installed, then the only way to not be guessing is to have it measured now, and your fan set accordingly.

  7. #7
    Coil is an Aspen CC48A.

    What I am hearing that that the actual CFM needs to be determined by measuring the ESP and performing the necessary calculations. Correct?

    With that said, should the actual CFM be set to 1400?

    Thanks again for all your input.

  8. #8
    Join Date
    Jul 2008
    Location
    RTP North Carolina
    Posts
    81
    Quote Originally Posted by will2008 View Post
    What I am hearing that that the actual CFM needs to be determined by measuring the ESP and performing the necessary calculations. Correct?

    With that said, should the actual CFM be set to 1400?
    Thats correct, CFM will be determined by measuring the ESP first, then using that value to set the fan speed based on your systems blower performance table. Your actual CFM should be close to 1400, keeping in mind 400 CFM per ton is just a general range to shoot for.

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