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  1. #1
    Join Date
    Dec 2011
    Location
    Hiram, Ohio
    Posts
    214

    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
    Location
    SW Wisconsin
    Posts
    4,977
    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
    Location
    Hiram, Ohio
    Posts
    214
    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
    Posts
    881
    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.
    Nothing is magic, it works or doesn't work for a reason.

  5. #5
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,574

  6. #6
    Join Date
    Sep 2009
    Location
    Arnold mo
    Posts
    3,966
    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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