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  1. #1
    Join Date
    Dec 2011
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    Hiram, Ohio
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    another comment / question pertaining to airflow

    In looking at the physical dims. of my pending system, I find it surprising that my furnace (20" x 20" outlet) with my matched coil (20" x 20" inlet) actually only has a 14" x 16" inlet due to the drain pan. That it a huge restriction. And, that drain pan is essentially a flat surface. Why don't the manufacturers at least make a kit that allows the installer to add some sheet metal to the inside of the furnace to "funnel" the air to this smaller opening, making it more aerodynamic? It is a 400 square inch to 224 square inch "hard" transition. Could at least make it more gentle with some funneling. reminds me of a 40 year old semi truck with a flat front end. Do any of you ever fabricate your own "funneling system"?

  2. #2
    Join Date
    Jun 2005
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    SW Wisconsin
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    Quote Originally Posted by troyport View Post
    In looking at the physical dims. of my pending system, I find it surprising that my furnace (20" x 20" outlet) with my matched coil (20" x 20" inlet) actually only has a 14" x 16" inlet due to the drain pan.

    That it a huge restriction. And, that drain pan is essentially a flat surface. Why don't the manufacturers at least make a kit that allows the installer to add some sheet metal to the inside of the furnace to "funnel" the air to this smaller opening, making it more aerodynamic? It is a 400 square inch to 224 square inch "hard" transition.

    Could at least make it more gentle with some funneling. reminds me of a 40 year old semi truck with a flat front end. Do any of you ever fabricate your own "funneling system"?
    An interesting post, for which I too have also wondered why not a transition.
    The air hitting the evap-pan must cause considerable turbulence...would think mfg'ers would consider offering a kit...

    Without any air circulation on it, the bottom of the evap-pan would need to be well insulated or it would probably condense a lot of moisture.

    That goes from 2.77-sf to 1.55-sf. What CFM is going through that restriction? 3-Ton 1200-CFM / 1.55 is 774-fpm velocity into the coil.

    It is also important that all the evap coil circuits get the same CFM of airflow through each of them.

    Hopefully, there will be a considerable number of viewpoints expressed on this one...

  3. #3
    Join Date
    Dec 2011
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    Hiram, Ohio
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    Glad I am not the only one who has thought of this.. And I would be interested in everyone's thoughts on this as well. I suppose since this is a 2-stage system, it won't be pushing maximum air a lot of the time.. but still that turbulence! Any other thoughts?

  4. #4
    Join Date
    Dec 2004
    Location
    Caledonia WI
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    I've been making transitions under a coils for over 30 years, but it's getting harder to make a useful transition under these new skyscraper coils and still fit it within the constraints of the building.
    It's not what you're capable of doing that defines you, it's what you do on a daily basis.

  5. #5
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    Sep 2008
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  6. #6
    Join Date
    Sep 2009
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    Arnold mo
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    I can't imagine it is a design flaw. The equipment is tested in laboratories and it functions to specs; if it didn't, they would re-design it. Your time would very likely be better spent at looking at the design flaws in your duct system, and as a logical extension of that thought, look into flaws in your building envelope.
    An answer without a question is meaningless.
    Information without understanding is useless.
    You can lead a horse to water............
    http://www.mohomeenergyaudits.com

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