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  1. 10-24-2005, 11:19 AM #1
    jimfx
    jimfx is offline Regular Guest
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    Question

    I just got a new furnace installed and I am wondering if I have enough return air volume for my system. I have a 100,000 BTU Carrier 96% eff. furnace. What should my minimum return duct size be?
    Thanks
    JimFx
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  2. 10-24-2005, 12:51 PM #2
    jimfx
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    I can't believe no one has a rough guess as to what the minimum return duct size needs to be on a 100,000 BTU furnace . . . or should I be posting under another heading?
    Thanks
    JimFx
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  3. 10-24-2005, 01:13 PM #3
    eapples
    eapples is offline Regular Guest
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    Return Duct Size

    Originally posted by jimfx
    I can't believe no one has a rough guess as to what the minimum return duct size needs to be on a 100,000 BTU furnace . . . or should I be posting under another heading?
    Thanks
    JimFx
    Jim: I am not a hvac person. But I've developed a habit of reading the owner's manual for all the hvac equipment in my home. I believe that somewhere in the owner's manual/installation instructions all the technical specifications would be mentioned, particularly sizing heating/cooling ducts and return air ducts. Also, if your hvac contractor is an ethical person he would tell you if your returns are undersized for your unit before he installed the unit.
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  4. 10-24-2005, 02:06 PM #4
    dash
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    Jim ,a Manual D calculation,from ACCA ,would be required to tell you the correct size.This requires counting the fet and equivelent feet for turns and fitting ,for the entire duct system,which we can't do from here.It also depends on the type grilles and the actual cooling coil installed if any,filter size/type etc.,etc..

    Now an educated guess would be,for a furnace requiring 1525 cfms @100,000 btus,you need from 20X12 to a 25X12 return duct,could need even larger,not likely any smaller.


    Have the "temperature rise" checked by a Pro,while getting your annual "checkup"and that will let you know if you have enough airflow.
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  5. 10-25-2005, 06:23 PM #5
    jimfx
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    Thanks for the info. Your rough estimate is a big help.
    JimFx
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  6. 10-25-2005, 06:33 PM #6
    curry
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    Your return drop should be no less than 200 sq inches.

    Sttandard drop size for this application is 24x10 with a 16x25 fiter and same size opening on throat of boot.

    The trunk should be a minimum of 24x8.
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  7. 10-26-2005, 08:36 AM #7
    dash
    dash is offline Banned
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    Originally posted by curry
    Your return drop should be no less than 200 sq inches.

    Sttandard drop size for this application is 24x10 with a 16x25 fiter and same size opening on throat of boot.

    The trunk should be a minimum of 24x8.

    Better to have a Pro do the Manual D calcs,and size just right.
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