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  1. #1
    Join Date
    Mar 2005
    Posts
    18
    i got the final of the 3 bids for an install of a new central air system. we don't have an existing system to replace so there isn't a previous configuration that can be considered.

    with the 3 bids i got the following:

    3 ton 11 SEER unit
    4 ton 12 SEER unit
    2 1/2 ton 14 SEER unit

    what is the relationship between the ton and the SEER rating of a particular unit?

    i'm guessing the ton is a result of the load calculation done. i'm surprised by such varied results. 2 1/2 - 4 ton seems like to be a big difference. is it?

    thanks.

  2. #2
    Join Date
    Sep 2002
    Location
    South Dakota
    Posts
    6,579

    There is no relationship between tonnage and SEER. Tonnage is cooling capacity and SEER is an efficiency rating.

    Sort of like comparing the capacity of your automobile gas tank to miles per gallon. One gives you gasoline tank capacity and the other gives you efficiency in the use of each gallon. There is no relationship between the size of a gas tank and the mpg rating of the car.





    [Edited by NormChris on 03-17-2005 at 11:50 PM]

  3. #3
    Join Date
    Feb 2005
    Location
    In a van by the river
    Posts
    621
    As Normchris said SEER is efficiency and ton is capacity, however to use his example, you will not need the same size fuel tank on a hybird in comparison to a Suv to go 300 miles. Basically, what a 10 Seer 4 ton unit can put out in BTU, a smaller 3 ton 14 Seer (example) can do the same. It's BTU input rated but the output is what matters. Ask them to do a heat load calc (Manual J).
    ## + years in the field never made you a know-it-all This industry is far more diverse than you are

  4. #4
    Join Date
    Feb 2005
    Location
    In a van by the river
    Posts
    621
    Sorry just wanted to simplify. A 80% efficient 3 ton (36000 BTU) unit will have an actual 28800 BTU output. A 3 ton 90% efficient unit would put out 32400 BTU, So more SEER the less rated input ton required
    ## + years in the field never made you a know-it-all This industry is far more diverse than you are

  5. #5
    Join Date
    Mar 2005
    Posts
    18
    is the heat load calc (Manual J) the method where the person measures the window sizes, where they face (North, South, etc.), how many vents, temperature reading (some laser gadget thing), etc. are taken. then results are entered into a computer software for the evaluation?

    if that is it, only one of the 3 performed such test. they were the 2 1/2 ton 14 SEER bid.

    one just looked at the information that the county assessor had on our house and came up with the 4 ton 12 SEER.

    the other just interviewed me as 2 how many vents the house had, etc. and came up with 3 ton 11 SEER.

  6. #6
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    Originally posted by git-r-dun
    Basically, what a 10 Seer 4 ton unit can put out in BTU, a smaller 3 ton 14 Seer (example) can do the same. It's BTU input rated but the output is what matters.
    This is not correct at all.

    The AC side of things doesn't work like the heating side. It isn't like gas furnaces where they are rating the % of the BTU input that makes it into the air. It is based on elecric usage, there is no correlation whatsoever between the capacity and the SEER rating.

    A 4 ton 10 SEER system and a 4 ton 14 SEER system will have roughly the same cooling capacity, just the 14 SEER will use less electricity to do it.

    A 3 ton 14 SEER system would have roughly 12,000 BTUs less cooling capacity than a 4 ton 10 SEER unit.
    If more government is the answer, then it's a really stupid question.

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,095
    Ask to see the load calc if they say they did one.
    If they say they don't give them out till the contract is signed, then tell them that the calcs are to far apart, and you want to see who really did one, and who is guessing.

    You can do your own, click the bulls eye at the top.

    As most of the others said, seer means nothing towards capacity.

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    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  8. #8
    Join Date
    May 2002
    Location
    MEDIA PA
    Posts
    1,381
    Ask to see a heat load. Better on this site you can do it four forty dollars. SEER is to your A/C as gas mileage is to your car. Tonnage is amount.

  9. #9
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,346
    I can only add to what the others have said: click on the bull's eye at the top of this web page and download your own copy of HVAC-Calc Residential 4.0. This program is well written and will allow you to plug in the data for your own home to the best of your knowledge. You live in your home, you likely know it better than anyone (which rooms are hottest or coldest, how much insulation you have, etc.).

    You can then take your results and compare them to any heat load calc done by a contractor (sounds like only one so far).

    P.S. if you get a guy that comes out to give you an estimate and find him standing across the street on the curb, holding up fingers to see how many cover up your house to determine tonnage size, tell him with syrupy sweetness in your voice to have a nice day, don't call us, we'll call you.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  10. #10
    Join Date
    Jul 2002
    Location
    Zelienople, Pa
    Posts
    2,965
    Originally posted by mudbog
    is the heat load calc (Manual J) the method where the person measures the window sizes, where they face (North, South, etc.), how many vents, temperature reading (some laser gadget thing), etc. are taken. then results are entered into a computer software for the evaluation?

    if that is it, only one of the 3 performed such test. they were the 2 1/2 ton 14 SEER bid.

    This is your new contractor.
    Congratulations!
    How tall are you Private???!!!!

  11. #11
    Join Date
    Apr 2004
    Posts
    7,680
    Originally posted by git-r-dun
    Basically, what a 10 Seer 4 ton unit can put out in BTU, a smaller 3 ton 14 Seer (example) can do the same. It's BTU input rated but the output is what matters. Ask them to do a heat load calc (Manual J).

    Sorry just wanted to simplify. A 80% efficient 3 ton (36000 BTU) unit will have an actual 28800 BTU output. A 3 ton 90% efficient unit would put out 32400 BTU, So more SEER the less rated input ton required
    Where did you get this? Tell us you just made this up 'cause it sounded good.

  12. #12
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,346

    doc

    Where did you get this? Tell us you just made this up 'cause it sounded good.
    I think the handle "git-r-dun" says it all.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  13. #13
    Join Date
    Feb 2005
    Location
    In a van by the river
    Posts
    621
    Thanks for the correction guys, I'm glad I atleast threw the manual J out there because that was pretty dumb. I guess my motto is what it is because quite honestly I did think ac was the same with heat as far as efficiency and output goes. Thanx again...
    ## + years in the field never made you a know-it-all This industry is far more diverse than you are

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