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  1. #1
    Join Date
    Sep 2012
    Posts
    8

    Sizing for a replacement air conditioner, do i need a full replacement?

    situation: my old a/c, 2 ton system, is not blowing cool air, the outdoor unit runs, is about 28 years old, but does not cool-
    i assume there is leak of coolant, since the unit is so old, i'm have gotten 2 bids for a replacement: outdoor compressor and coil, for a 2 ton, estimator did not say i need
    a different size of equipement,

    the second bid ended up to be for a 2.5 ton, reason: the estimator measured the total cooled area ( about 1000SF) and his computer calculations insist on a bigger unit, but the original furnace will be used -

    questions:

    1.shall i get new compressor, coil, furnace (about 18 years)
    2. if new furnace, why,
    3. who is correct with sizing the unit? here is more info: house '84, no new insulation, ranch style, 3 windows shaded by porch, 1 window and sliding door- north orientated, 1 window - west
    4. will the old furnace work with the higher sized 2.5

    what questions shall i ask the estimator?

    thanks,

    B

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,918
    Have you cooled fine all these years til now? If so, stay 2 ton. Usually most duct systems are borderline for what you have so if you go 25% bigger, you need to add 25% to your duct system and number of supply & return outlets. Did he tell you that? My 1000 sq ft house from 1988 I can hang meat in 100° weather with a 2 ton. With north facing, shaded windows and only 1 window facing west, sure doesn't sound like much of a load.

    You need at least new unit & coil. If furnace is solid and you don't want to change it, keep it as long as it blows enough air for the size A/C you choose. You'd likely need to stay 13/14 SEER with existing furnace as you won't get much more without high end blower motor.

  3. #3
    Join Date
    Sep 2012
    Posts
    8

    sf of house, relation to unit

    Quote Originally Posted by BaldLoonie View Post
    Have you cooled fine all these years til now? If so, stay 2 ton.

    ]we used the a/c conservatively, i would say the cooling was mediocre, the sales person saw also two flex ducts with tethered cover lining[/I][/B]Usually most duct systems are borderline for what you have so if you go 25% bigger, you need to add 25% to your duct system and number of supply & return outlets. Did he tell you that?
    yes, but he said the duct system was ok for the 2.5 ton

    My 1000 sq ft house from 1988 I can hang meat in 100° weather with a 2 ton.

    [B]my house is 1250sf, not counting the uncooled closets,space of framing it
    comes to a bit more of 1000SF

    With north facing, shaded windows and only 1 window facing west, sure doesn't sound like much of a load.

    You need at least new unit & coil. If furnace is solid and you don't want to change it, keep it as long as it blows enough air for the size A/C you choose. You'd likely need to stay 13/14 SEER with existing furnace as you won't get much more without high end blower motor.
    he old unit is a 10 seer, the quote for the new is a 13 seer

    the salesperson mentioned that the furnace needs to have a certain power?to work
    the unit properly?

    so what would is he talking about? any idea?

    thanks for the quick reply- B

  4. #4
    Join Date
    May 2008
    Location
    Missouri
    Posts
    3,425
    He's probably talking about the fan on the older furnace. I'd also recommend staying with the 2 ton AC as the old furnace worked fine with this size and going to larger AC could cause problems with air distribution (blower or ductwork). 13 SEER is now the minimum efficiency you can purchase.

  5. #5
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,918
    Got a model # of your furnace?

  6. #6
    Join Date
    Oct 2004
    Location
    So Cal
    Posts
    3,473
    If the furnace is also 28 yrs old- I'd replace it at same time as a/c.

  7. #7
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,158
    2 tons is plenty for 1,000 sqft in most areas/homes. I just installed a 2 ton in my 1600sqft house, keeps it 75 on a 100degree day. If the furnace is 18yr old I'd replace it also.

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