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  1. #14
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    Jan 2004
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    Lancaster PA
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    Quote Originally Posted by kurtnm View Post
    Thanks for the help. How many tons would that (80K) be? (Current BTUS on furnace is 162,000, it's 24 years old.)

    The reason I didn't go with the proposal I received is two contractors told me I could go quite a bit smaller, one told me I could probably go about 3.5 tons. (Unfortunately, he never got me a bid.)
    Depending on brand, it can be 3, or 4, tons.
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  2. #15
    Join Date
    Nov 2012
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    18
    I got a verbal quote today and the contractor was recommended 4 ton furnace (120k btu) and 4 ton AC, 2-stage for both. I was originally thinking about a modulating 80% furnace, but in a less expensive brand. He liked Carrier. It's a bit pricey. He didn't do any sort of load calc or seem to be interested in doing it. We have cathedral ceilings, it's 2000 sq. feet but a big volume.

  3. #16
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    Jan 2004
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    Lancaster PA
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    Without a load calc, no way to know what size you really need.
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  4. #17
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
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    2,654
    In what state do you live? Where is your condo located in the complex? In other words, do you have a condo above, below or beside you?

  5. #18
    Join Date
    Aug 2012
    Location
    North Dakota
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    518
    ya I see no need to do due dilagence when I am asking my customer to spend lots of their hard earned money or how did you say it (carrier a bit pricey) though what the hell he may not be interested in doing a quality install anyway

  6. #19
    Join Date
    Nov 2012
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    18
    Quote Originally Posted by George2 View Post
    In what state do you live? Where is your condo located in the complex? In other words, do you have a condo above, below or beside you?

    We have a smaller unit below part of our unit, and nothing above us. We have an east-west exposure, in NM. I would like to get a load calc but that's another cost, and so far I haven't found a contractor offering to do one. Original windows and doors and typically southwest insulation levels, which is not as high as you would see in the north. Even with a five ton (both furnace and AC) there are periods of time where it can run pretty much continuously, both summer and winter, during the extremes of each season. This is generally the exception, however. The contractor questioned wether we are really getting 5 tons of performance, especially out of the AC. My gut says going smaller than 4 tons would probably be a mistake, but it's right on the edge of 3.5 to 4. He said 2-stage work well with multiple level units like ours. He said that if we went single stage AC (we are unlikely to do so) he would probably go with a 3.5 ton AC. If we go 2-stage he would recommend a 4 ton, and I'm not clear what his reasoning is for the difference. We are stuck using the original lines to the condenser for the old system, and would have to purge them.

    Also, none of our system communicates right now, each component is a different manufacturer, the furnace is Trane (original), AC is Bryant (probably original), and the condenser is Lennox, newest component (late 90s to 2002) but still not good quality. We are at 9 Seer according to the contractor. The new system would be fully communicating, of course.

  7. #20
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
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    2,654
    Quote Originally Posted by kurtnm View Post
    We have a smaller unit below part of our unit, and nothing above us. We have an east-west exposure, in NM. I would like to get a load calc but that's another cost, and so far I haven't found a contractor offering to do one. Original windows and doors and typically southwest insulation levels, which is not as high as you would see in the north. Even with a five ton (both furnace and AC) there are periods of time where it can run pretty much continuously, both summer and winter, during the extremes of each season. This is generally the exception, however. The contractor questioned wether we are really getting 5 tons of performance, especially out of the AC. My gut says going smaller than 4 tons would probably be a mistake, but it's right on the edge of 3.5 to 4. He said 2-stage work well with multiple level units like ours. He said that if we went single stage AC (we are unlikely to do so) he would probably go with a 3.5 ton AC. If we go 2-stage he would recommend a 4 ton, and I'm not clear what his reasoning is for the difference. We are stuck using the original lines to the condenser for the old system, and would have to purge them.

    Also, none of our system communicates right now, each component is a different manufacturer, the furnace is Trane (original), AC is Bryant (probably original), and the condenser is Lennox, newest component (late 90s to 2002) but still not good quality. We are at 9 Seer according to the contractor. The new system would be fully communicating, of course.
    I agree with your contractor that you're not getting the full capicity out of your furnace and A/C because of the return air (for sure) and maybe a short supply side as well.

    I tend to agree also with the 3.5 ton single stage or better yet the 4 ton 2-stage. The reason for the 2 stage is that you'll have the extra A/C when you need (and pease of mind) and it'll run on the low stage (better dehumidification) the majority of the time.

    Running the extra low voltage wires may be an issue.
    Last edited by George2; 11-14-2012 at 11:47 AM. Reason: spelling error

  8. #21
    Join Date
    Jan 2009
    Location
    Keokuk, IA
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    5,520
    Quote Originally Posted by kurtnm View Post
    I got a verbal quote today and the contractor was recommended 4 ton furnace (120k btu) and 4 ton AC, 2-stage for both. I was originally thinking about a modulating 80% furnace, but in a less expensive brand. He liked Carrier. It's a bit pricey. He didn't do any sort of load calc or seem to be interested in doing it. We have cathedral ceilings, it's 2000 sq. feet but a big volume.
    High ceilings present air distribution rpoblems, but don't add all that much additonal load depending on how it's constructed and insulated. Windows, doors and air leaks along with using the correct design temperature and conditions, have the biggest impact. Its' also not square footage that as important as the total wall area and shading. So a 1 story 2000 sqft home would have a higher heat loss/gain than a 2 story home the same size. Similarly, a 2000sqft home will not need anywhere near 2X the capacity as a 1000sqft home.

    square footage is easy to measure, but a poor measurement for determining capacity.

  9. #22
    Join Date
    Nov 2012
    Posts
    18
    Quote Originally Posted by George2 View Post
    I agree with your contractor that you're not getting the full capicity out of your furnace and A/C because of the return air (for sure) and maybe a short supply side as well.

    I tend to agree also with the 3.5 ton single stage or better yet the 4 ton 2-stage. The reason for the 2 stage is that you'll have the extra A/C when you need (and pease of mind) and it'll run on the low stage (better dehumidification) the majority of the time.

    Running the extra low voltage wires may be an issue.

    I got another quote, and the recommendation is a 4-ton single stage from this contractor. He says the variable speed fan is the biggest factor when it comes to noise. (The Coleman model he recommends has a truly variable speed fan, not just high/med/low.)

    Can you explain the low voltage wiring issue with the 2-stage AC? Is that to the condenser?

  10. #23
    Join Date
    May 2006
    Location
    Philadelphia, PA
    Posts
    1,384
    You need a manual J load calculation and thorough assessment of all ducts that can be accessed. Any other sizing method is a guess and could possibly leave you with a system that does not perform as expected.
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  11. #24
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
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    Either your new contractor doesn't know what he's talking about or he is trying to mislead you.

    All variable-speed motors are like a reastat (sp?) on a light. There are no high/med./or low, thus the "variable" speed terminolgy (sp?). Sorry about the spelling.

    The advantage of a 2-stage is that the blower (nise) will normallt be on a lower speed (less noise). A 4 ton single -stage will run at 1,600 cfm were as a 2-speed will run approx. 1,200 cfm.

    The 2-speed needs 2 addition low voltage wires to work.

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