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  1. #1
    Join Date
    Nov 2010
    Location
    Ontario, Canada
    Posts
    61

    Horizontal Furnace - How long for supply air plenum?

    I was looking at the possibility of mounting a high efficiency furnace horizontally in a garage as opposed to a unit heater at a customers request. I've heard guys talk about a minimum length for the supply air plenum but do not see anything in the manual for the unit I was considering.

    Is there a standard minimum and what are the reasons?

  2. #2
    Join Date
    Mar 2011
    Location
    Galveston Texas
    Posts
    530
    Depends on the number of ducts coming off of it, as well as available room. The more ducts the longer the plenum. Ours are a min 4' long, I know the pre-fabricated ones the supply houses carry are only 3'.

  3. #3
    Join Date
    Jun 2004
    Posts
    873
    We leave at least a foot at the end
    To build static and more balance output.

  4. #4
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    4,266
    i can speak for rheem. they want at least an 18" plenum before any bends, takeoffs, etc...

    turning vanes and proper take offs are the only way to go.

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