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  1. #1
    Join Date
    May 2005
    Location
    Santa Clara, CA
    Posts
    2

    Question

    So I'm getting a bid for AC & new furnace (22 year old furnace, adding AC)

    It's a tight fit, and the guy doing the bid was doing a lot of measuring, and checking for fit for it.
    But looking at the Carrier website for the parts he spec'd in the proposal, I'm thinking they're mismatched.

    58CAV0701-12 Carrier furnace
    38HDL036 Carrier 3ton 10SEER
    3K5AXA036017 Carrier Coil

    http://www.commercial.carrier.com/co...PRD721,00.html
    http://www.xpedio.carrier.com/idc/gr...0-2002-50x.pdf

    The installation will be a down-flow system.
    It's in a tight space in the 2nd-floor, un-insulated space (roof comes down on that section of the house, making it only usable really for storage/mechanicals)

    If I'm reading the above links correctly, the coil is 17", while the furnace is 14". So I'll have a furnace 3" narrower than the coil? Is that normal/acceptable?

    I'm also concerned that he may be over-sizing the cooling system - I've got a 1200BTUh window AC that mostly cools the house. (cold in the upstairs room; OK to a little warm downstairs) Going from 1 ton to 3 ton seems like overkill.

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,540
    Did he do a Manual J, if not insist on 1 being done.
    You can do your own, click on the bulls eye.

    Some times a wider coil is used, but not too often.

    Not familar with Carrier enough to tell you what coils they might have for better match up.
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  3. #3
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    For proper airflow,it's best to have a metal "transition" between the furnace and the coil,when sizes differ.

  4. #4
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,962
    Agreed, especially in the downflow position you want room for the air to be able to distribute evenly around the top of that "A" coil.

    Otherwise, there is nothing wrong with a coil being a different physical size the furnace.
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  5. #5
    Join Date
    May 2005
    Location
    Santa Clara, CA
    Posts
    2
    Originally posted by dash
    For proper airflow,it's best to have a metal "transition" between the furnace and the coil,when sizes differ.
    I don't think there's enough room for transition.
    Return is coming from side, sloped roof right above.
    So any transition piece raises the furnace, and that eats into the square area of the return duct (just before it makes the right angle to come down into the furnace.)

    As for doing my own calc - I started to, but $50 for the software just to do my house seems pretty steep to me. I don't get the "infiltration" or wall or total without spending $50. Especially when it *should* just be a double-check of someone else's work.


  6. #6
    Join Date
    Apr 2005
    Location
    AZ
    Posts
    192
    But if you spend the 50 bucks and you find the unit is not the coreect size (assuming your calcs are correct) that will be some good money spent. Whats 50 bucks when looking at the whole project.I wouldnt think twice about spending 50 before spending thousands if there was any doubt about whether or not what i was getting is correct.

  7. #7
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304

    Penny wise...

    The cost to YOU as a homeowner, of something being not right, will be far in excess of $50 most likely. I think you should reconsider paying the $50 as research to make sure you are getting what you need. This is coming from a homeowner, I have paid the $50 and it was well spent.

    If you are unwilling to do a Manual J, or to get one done, then it is unreasonable to ask whether 3 tons is a good choice. This is pretty much the only way professionals know.

    Best of luck -- P.Student

  8. #8
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,635
    As indicated, relax about the coil size. The actual opening of a 17 inch coil matches the discharge of a 14 inch furnace better than a 14 inch coil. You'll get better airflow through the 17 inch coil than you will the 14.

    If you want to talk AC sizing call me. I'll be up for a few hours yet. My phone number is easy enough to find.

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