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  1. #1
    Join Date
    Feb 2015
    Posts
    16
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    confused airflow

    New install and new ductwork. Ductwork is 14" supply and return. Static pressure is .31 total on medium fan speed. .30 on high speed. Medium speed cfm total on supply is 473 and 314 on the return. High speed is 413on supply and 332 on return. 2.5 ton Carrier heat pump package. Does this make since to anyone? Please advise.

  2. #2
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    9,806
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    Restriction inside the unit, probably the door insulation sucked against the blower. Could be a piece of insulation on the indoor cool. There's definately an internal restriction with that low of TESP and 14" duct.

  3. #3
    Join Date
    Feb 2015
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    16
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    That is what we thought at first too. Checked it and that's not it.

  4. #4
    Join Date
    Sep 2007
    Location
    edmonds wa
    Posts
    2,448
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    Fan going backwards?

  5. #5
    Join Date
    May 2014
    Location
    Bay Area California
    Posts
    4,989
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    The first thing I would ask is why are you checking the statics and airflows? There must be something wrong or the system isn't preforming up to par (?).

    Next, you state that total static is less with the blower on high. That would indicate a venturi action is messing with your readings.

    Regarding CFM, how are you measuring that? The gold standard through the years is to use a pitot tube to measure FPM and take multiple readings on a grid pattern then average the readings. After that, you can convert the FPM to CFM. There are a lot of tricks to getting the correct numbers, but suffice it to say I have seen negative pressures in a supply duct.


    Quote Originally Posted by dirtbag1369 View Post
    New install and new ductwork. Ductwork is 14" supply and return. Static pressure is .31 total on medium fan speed. .30 on high speed. Medium speed cfm total on supply is 473 and 314 on the return. High speed is 413on supply and 332 on return. 2.5 ton Carrier heat pump package. Does this make since to anyone? Please advise.

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