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    Question

    5 ton 120k BTU furnace. 2 year old house
    HO has pretty low airflow through the registers, everything seems to be sized properly on the main branches for supply and return, but there's around 24 supplies in this home all with 6" round and 4x12 registers, and the return is all properly sized up above, but when it transitions into the return 90 at the unit, it tapers way down (I'm guessing because there is a clean out in the way). It, also has a 12 inch round return for the basement on the other side of the furnace not in the picture. I'm wondering if this place has too many registers or if this trainsition on the return could be the culprit, any thoughts?
    The airflow at the registers seems okay but it definently feels less than normal. It's pretty loud when it runs too. Thanks!
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  2. #2
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    Any measurements made, TESP, airflow, etc.?
    If I do a job in 30 minutes it's because I spent 30 years learning how to do that in 30 minutes. You owe me for the years, not the minutes.

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    Let me guess.
    This system has always had low airflow because it was designed to have low airflow.

    Return air should enter a 5-ton upflow blower from both sides of the blower compartment
    or through the bottom of the blower compartment.

    Unless there's another return on the right side of the furnace that I can't see...
    I've already been wrong six or seven times today!
    "Compressors never die; they're always murdered!" - Glenn Hannegan Jr

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    Quote Originally Posted by Spide View Post
    Let me guess.
    This system has always had low airflow because it was designed to have low airflow.

    Return air should enter a 5-ton upflow blower from both sides of the blower compartment
    or through the bottom of the blower compartment.

    Unless there's another return on the right side of the furnace that I can't see...
    I've already been wrong six or seven times today!
    Yep 12 inch round on the other side basically 90s straight into the return grill downstairs with a 16x20x1
    The pictures filter is 16x25x1

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    Is the only problem low airflow from the supply diffusers?
    The owner wants to feel the air coming out of the vents?
    What did the owner say the problem is??
    "Compressors never die; they're always murdered!" - Glenn Hannegan Jr

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    Quote Originally Posted by Spide View Post
    Is the only problem low airflow from the supply diffusers?
    The owner wants to feel the air coming out of the vents?
    What did the owner say the problem is??
    They're ac leaks refrigerant so it was a no cooling call, but theyre side complaint was airflow, theyre up and running now with the leak fixed

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    What was wrong with the airflow according to the owner?
    What criteria was the owner using to determine he has low air flow?
    "Compressors never die; they're always murdered!" - Glenn Hannegan Jr

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    what spiderman said!! not enough return, should be both sides or the bottom. should be wording for that in the manual.

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    With 24 diffusers airflow per diffuser will probably be less than 100 CFM even with no duct problems. If the house cools properly there is no reason to worry about the airflow per grille. With that many diffusers the loud noise is most likely in one area. That appears to be at the furnace return. That doesn't necessarily mean mods have to be made to the duct to get enough airflow. The noise is whatever the owner can tolerate as long as flow isn't overly restricted.
    No man can be both ignorant and free.
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    Quote Originally Posted by 71CHOPS View Post
    what spiderman said!! not enough return, should be both sides or the bottom. should be wording for that in the manual.
    It does have return on the other side.

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    OK, my question is, the return duct gets narrower and then goes into the 90* then into the unit, Is this normal in some areas? All of the systems here that I work on, the return doesn't reduce down like that, even the commercial systems, unless they split off, and I am pretty sure, when you restrict the airflow, the system gets louder also.

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