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  1. #1

    fitting new coil to furnace

    Hi all,

    I'll be purchasing a new A/C split system. The furnace is horizontal in the attic and is 14.5" wide. The new evap coil case is 17.5" wide. My guess is that you'd want a transition adapter from the furnace to the coil. But space may be an issue.

    What if the installer wants to attach the coil case directly to the furnace and just cap the overhang. Is that an acceptable way of doing things? The A-coil opening is around 9".

    Thanks for any opinions.

  2. #2
    Join Date
    Jun 2006
    Posts
    491
    it needs a transition to be correct. a lazy installer would tell you otherwise. i'd think about replacing the furnace too unless it's really new.

  3. #3
    Thanks for the input! That's what I figured. The furnace is a 12 year old
    XE80 in good shape (mild winters). I'd love to go with a new variable speed unit but it's hard to justify the cost as we'll be moving in 2-5 yrs.

  4. #4
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,418
    Those are a good furnace. I'm with Horsey, a good installer can make a nice transition to the wider coil. More work but the right way.

  5. #5
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    2,998
    Our guys carry what they call 'blanks' on their trucks.
    Plain sheetmetal strips..and insulated sheetmetal strips.
    If they use an uninsulated blank they insulate it externally.
    All seams & joints are mastic sealed.

    I've seen the oversized openings closed off with duct tape and
    foil tape. Neither last long.

    Best of luck to you.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  6. #6
    Join Date
    Feb 2004
    Location
    chicago suburbs
    Posts
    4,422
    Quote Originally Posted by energy_rater_La View Post
    Our guys carry what they call 'blanks' on their trucks.
    hack-olicous.
    FILL OUT YOUR PROFILE!!

  7. #7
    Join Date
    Apr 2008
    Posts
    52
    Quote Originally Posted by tinner73 View Post
    hack-olicous.

    Yeah,its called metal board. we just stick the corners together and stick some tin tape to connect it. But its kind of embarassing telling the builder he cant pressure test

  8. #8
    Join Date
    Feb 2004
    Location
    chicago suburbs
    Posts
    4,422
    Quote Originally Posted by DuctDude View Post
    Yeah,its called metal board. we just stick the corners together and stick some tin tape to connect it. But its kind of embarassing telling the builder he cant pressure test


    sweet......my job is safe.
    FILL OUT YOUR PROFILE!!

  9. #9
    Join Date
    Aug 2005
    Location
    San Diego,CA
    Posts
    284
    Residential HVAC Questions and discussions pertaining to HVAC for the home. No pricing, no DIY, please read Site Rules Register
    Sink or Swim!
    A Man has to know his limitations..
    To be old and wise, one must be young and dumb..

  10. #10
    Join Date
    Jan 2001
    Location
    Pamnyra VA.
    Posts
    709
    get the right coil size . i don't think the openings have changed size.

  11. #11
    Join Date
    Jun 2007
    Location
    Round Rock
    Posts
    3,411
    The coil should have recommended installation instructions and how to handle this situation. Given that you have stated there is limited space. A small transition probably will not make any difference. It's like an upflow furnace and coil that do not match. You do not build a transition for that, but there are instructions that deal with the manufacturer's recommended way to handle this. The coil might be shifted to the left or right. The same with the horizontal. It might hang a little low or sit a little high. Just do as the instructions say and all should be well.

  12. #12
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    2,998
    It seems to be standard procedure for the crew...
    2 of the crew make the transitions in the sheet metal shop.
    I think the 'blanks' are for unforseen issues.
    I do know that they screw them in place & mastic seal.
    Would this be consitered hacking??

    I test the ductwork when the work is done.
    Total duct leakage (return leakage also) is within Energy Star allocation.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  13. #13
    Join Date
    Feb 2004
    Location
    chicago suburbs
    Posts
    4,422
    yes ....it would.
    FILL OUT YOUR PROFILE!!

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