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  1. #1
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    Jun 2004
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    n. va
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    furnace total btus

    confused about how to tell total btus of this american standard single speed 2 stage gas furnace 80% AFUE model #AUD2B080A9362A. I looked at the specs online & it shows the first stage output at 41,600 btus & the 2nd stage output at 63,000 btus---so what are the total btus of this furnace? is it 63,000 + 41,600 = 104,600 btu or 80,000 btu?

    i ask because the american standard furnace will replace a 1983 carrier gas furnace model no. 58SS080-BC that states it is 95,000 BTU input, with furnace size at 080 BC. is this carrier furnace a 95k btu or an 80k btu? one contractor said the model number indicated it was 80k btu.

    also the american standard specs online says the AUD2B080A9362A uses a 17 x 25" filter. contractor wants to change size of my filter from 14 x 20 x 1" to 16 x 25 x 1" would it matter that it's not 17 x 25 x 1"?

    thanks!
    Last edited by darc; 06-26-2009 at 03:03 PM. Reason: addition

  2. #2
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    Jan 2009
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    17"x25" is not a standard filter size. The "filter".... more like a screen... that's preinstalled on the bottom of the furnace from the factory is 17"x25" because the dimensions of the furnace are roughly 17" wide X 25" deep.

    The best option is to have a 20 X x 25" x 5" media filter installed for a little more. The filters last up to a year and have a lot less resistance than the 1" filters.

    The furnace the tinstaller is proposing is 80k BTU input... which is 64k BTU output. You old 1983 furnace was probably something like 70% efficient so even wiht 95kBUT input, it's output was 66.5k BTU's. So both units are roughly the same size.... but you're blowing less hot air out the flue.

    By the way, did the contractor do a load calculation to determine if thsi unit is the correct size. Many furnaces are oversized. It's possible your home only needs a 60k BT furnace... and you could take advantage of tax credits and get a 95% furnace. a 95% 60k BUT furnace will put out 57k BTU's, which is only about 10% less than your existing furance.

  3. #3
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    Jul 2004
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    Massachusetts
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    A two-stage furnace is like having two speeds in your automobile transmission. You can only be in one gear at a time. Same with the furnace. You only get on size flame at a time. So low fire is about 67% of high fire or roughly 41,000 Btu's. High fire is maximum output, which in this case is roughly 80% of 80,000 Btu's. The furnace selected is going to provide much greater comfort due to the significantly longer heating cycles of the 67% low fire flame. Also the variable speed blower should be quieter and use less electricty, provided you have adequately sized ducts. I do agree with motoguy, any replacement furnace should be preceded by a load analysis on the home. Did a load calc yesterday for a replacement AC system on an existing gas furnace. The existing AC was properly sized at 3.0-tons but he gas furnace was huge at 125,000 Btu's input @ 80% = 100,000 Btu's output. The house called for 42,000 Btu's output. That means the blower on the furnace is sized for either 4 or 5-tons in all likelihood. So there you go. Someone didn't do a load calc, everyone who follows and tries to do it right can't possibly get it right until the furnace is changed. Then if the yokel who changes the furnace just grabs the numbers off the old one and puts in a new one to match, same problem all over again. Load anlysis is king. It's the foundation for a heating or cooling system.
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  4. #4
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    Jun 2004
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    n. va
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    so do i understand correctly the american standard gas furnace i am considering as one option (model AUD2B080A9362A) is a single speed 80% afue 3 ton unit, w/ 80k btu input but ONLY a 63k btu output/capacity? how will that work in a house that heated well & cooled well with a 24 yr old 83% afue 95k btu input & 79k btu capacity/output gas furnace (carrier 58ss080 110-BC), & a 22 yr old 2.5 ton ac (carrier 38ed030300)?

    the recent load calculation showed 28,968 btuh total cooling load, & 62,627 btuh total heating load.

    can you tell me what the seer rating was on that 1987 carrier model 38ed030300 2.5 ton condenser?

    thanks

  5. #5
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    Jan 2004
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    Lancaster PA
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    No, its 2 stage.

    Your old furnace was probably slightly oversized.

    On the coldest nights, did it cycle off, or have to run 24/7.
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  6. #6
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    Jun 2004
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    n. va
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    the existing furnance did not run 24/7.

    my 1st question is if the american standard model AUD2B080A9362A is only 64k btu output capacity? i understand that it is a 2 stage single speed 80% afue 3 ton unit, w/ 80k btu input.

    my 2nd question is: can you tell me the seer rating was on that 1987 carrier model 38ed030300 2.5 ton condenser?

  7. #7
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    80% of 80,000 is 64,000.
    Its not a single speed. Its a multispeed.

    Can't tell you the SEER of your old unit.
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  8. #8
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    n. va
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    beenthere, you asked if on the coldest nights, did it cycle off, or have to run 24/7? Would furnace be oversized if it cycled off on coldest nights?

    so is the TOTAL OUTPUT CAPACITY of the AUD2B080A9362A 64k btu?

    can anyone direct me to a website where i can read the specs of what the seer was of the 1987 carrier model 38ed030300 2.5 ton condenser? i can't get any info off carrier side on this older model. thanks

  9. #9
    Join Date
    May 2007
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    Dry as a bone Tucson
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    1987 carrier model 38ed030300

    started as a 10 more than likely a 4 by now.
    Some Talk, Some Do
    "keeping condensing pressures low and evaporator pressures high"
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  10. #10
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    Jan 2004
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    Lancaster PA
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    It it cycled off on the coldest days. Yes, its over sized.
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  11. #11
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    Jun 2004
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    n. va
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    acfixr, do you have a link to the spec for the 1987 carrier model 38ed030300 2.5 ton condenser?

    can anyone tell me if the TOTAL OUTPUT CAPACITY of the American Standard AUD2B080A9362A is 64k btu?

    thanks!

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