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  1. #1
    Join Date
    May 2008
    Posts
    84

    correct CFM setting for 4T heatpump

    what should be the correct CFM setting for 2 stage 4 Ton heat pump coupled with a Air handler with 20KW heating elements ?

    The blower is currently set to 2000 CFM for cooling and 2000 CFM for heating, but I find it a bit noisy as it is. It starts slow but quickly goes to maximum speed.

    The possible range is 1200, 1600, 1800 or 2000 CFM with a possible tweak of +10% or -15%.

  2. #2
    Join Date
    Jun 2008
    Location
    South,Tx
    Posts
    331
    1600 Cfm
    Matt 7:12 The Golden Rule
    "Do for others what you would like them to do for you. This summary of all is taught in the law and the prophets.

  3. #3
    Join Date
    Dec 2006
    Location
    Most likely somewhere South of you
    Posts
    38
    Quote Originally Posted by Delta313 View Post
    what should be the correct CFM setting for 2 stage 4 Ton heat pump coupled with a Air handler with 20KW heating elements ?

    The blower is currently set to 2000 CFM for cooling and 2000 CFM for heating, but I find it a bit noisy as it is. It starts slow but quickly goes to maximum speed.

    The possible range is 1200, 1600, 1800 or 2000 CFM with a possible tweak of +10% or -15%.
    average is 400/ton or 1600, your location matters, in humid climates you may go as low as 320/ ton for increased latent removal, dry climates as high as 420/ ton for higher sensible heat removal.
    NOW.......
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  4. #4
    Join Date
    Feb 2007
    Posts
    190
    Where are yiu located and what is the model number of your indoor and outdoor unit

  5. #5
    Join Date
    May 2008
    Posts
    84
    Quote Originally Posted by rponson View Post
    Where are yiu located and what is the model number of your indoor and outdoor unit
    Location is Montreal, Canada. Very Hot and humid in the summer and very cold in the winter

    Amana ASZ18 18SEER/48000btu/2-stage/HSPF-9.5/R410-a/Heat Pump
    Amana MBE2000 + 20kw/variable speed/electric furnace

  6. #6
    Join Date
    Jul 2007
    Location
    Tulsa, OK
    Posts
    986
    Heat Pumps require a 450 CFM per Ton for proper air flow at .50wc. You have to know your ESP before you have a reason to adjust the CFM per Ton dip switching. The measured ESP and converting from the fan curve from the air handler is the real deal. Until then, your just blowing in the wind with a guess.

  7. #7
    Join Date
    May 2008
    Posts
    84
    Quote Originally Posted by JBM1000 View Post
    Heat Pumps require a 450 CFM per Ton for proper air flow at .50wc. You have to know your ESP before you have a reason to adjust the CFM per Ton dip switching. The measured ESP and converting from the fan curve from the air handler is the real deal. Until then, your just blowing in the wind with a guess.
    but if I don't have the tools to measure the Static Pressure, is there another way to measure it? or to figure out if I have enough CFM to achieve top efficiency ?

    otherwise I will have to go with rules of thumbs. Someone suggested 1600 CFM for cooling and 1800 for heating

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,081
    Quote Originally Posted by Delta313 View Post
    otherwise I will have to go with rules of thumbs. Someone suggested 1600 CFM for cooling and 1800 for heating
    4 tons x 400 CFM per ton = 1600 CFM in cooling.
    4 tons x 450 CFM per ton = 1800 CFM in heating.

    Both are rules of thumb.

    Many brands use a blower slow down feature to increase discharge air temp in heating mode.

    Your installation is new.
    Let the tech make the adjustments.
    And then ask him to list what everything is set for.
    After adjusting blower speed, he should recheck the charge.
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