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  1. #27
    Join Date
    Sep 2012
    Posts
    71
    Quote Originally Posted by jtrammel View Post
    My house is ~1300 sq ft with a 2 1/2 ton ac and it is oversized, I have to run a dehumidifier in the summer bc the ac doesn't run long enough to keep the humidity down. I'm in upstate South Carolina with a summer design of 92F. I did a load calc and it came out to 20k btus, a little over 1 1/2 tons and I know of some problems I can fix to bring the calc down a little more.
    That is why i am sold on going with the 2 ton. On the initial load calculations, all three contractors said the current 3 ton was too much. Even though 2 of the 3 recommended 2.5 tons, I am convinced from reading these posts the many they are afraid to "undersize".

    Quote Originally Posted by RyanHughes View Post
    Net capacity on low can be as much as 75-80% of total capacity depending on the match-up with the unloading scroll compressors used in most 2-stage units. That's why you don't want to go with a 3 ton if that's not what the space requires. On low, you'd already be at a bit over 2 tons capacity, and you wouldn't achieve the long runtimes in low as desired for comfort.
    Quote Originally Posted by BaldLoonie View Post
    Just remember that those furnaces quoted aren't meant for 2 stage A/Cs. If you go that route, you should get the variable speed models.
    Yes sir, the proposal from both Trane and Bryant is for a 2 stage variable speed 97% gas furnace.

  2. #28
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,158
    1587sqft in Oklahoma and 2 tons is more than enough for the design temp of 96. AC will keep house @ 75 with a 100 degree outdoor temp but runs all the time to do it. Sizing is right on the money, house is much more comfortable during low load conditions because the smaller unit runs more often.

  3. #29
    Join Date
    Sep 2012
    Posts
    71
    Quote Originally Posted by 54regcab View Post
    1587sqft in Oklahoma and 2 tons is more than enough for the design temp of 96. AC will keep house @ 75 with a 100 degree outdoor temp but runs all the time to do it. Sizing is right on the money, house is much more comfortable during low load conditions because the smaller unit runs more often.
    Thank you for your input. I am 90% convinced to go with a 2 ton unit. Like mentioned, I think just having a new system will help alot.

  4. #30
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,921
    Ignore me, the warning about the wrong furnaces is for a different thread! Shouldn't have posted after 2 shots of rum last night

  5. #31
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,248
    Quote Originally Posted by Zomby View Post
    So what would your suggestion be from what you have seen me post? 2 ton single stage or 3 tom two stage? I would sure appreciate your opinion!
    Definitely a 2 ton IMO (with ~20,000 BTU/Hr sensible cooling load)

    A few caveats..
    Home will be maintained at ~20'F less than outside.

    At > 78'F indoor temperature, the cooling capacity of the system actually increases.

    A dry heat is expected in mid-Missouri at > 95'F, so the air handler will operate at a higher Sensible Heat Ratio (SHR) inherently providing
    slightly larger capacity to cool the supply air.

    > 98'F in mid-Missouri should be much less than 2% of the time / significantly < 170 hours per year.
    i.e. 20 days per year for 6 hours a day.
    Worst case IMO One might expect 80'F inside for up to 15 days for 4 hours in these days of climate change.
    - use a fan for 100 hours per year if need be.-

    Those are the weather, equipment and homeowner interaction possibilities.

    So, I would go with a 2-ton because I very much like Ithe other 2,500 + cooling hours to be
    close to 40% Relative Humidity at ~76'F
    which can be achieved with run times of > 10 hours per day.
    .... without having the utility as the designated charity.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  6. #32
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,248
    Quote Originally Posted by BaldLoonie View Post
    Ignore me, the warning about the wrong furnaces is for a different thread! Shouldn't have posted after 2 shots of rum last night
    Confusing thread are you? ... easily done EVEN without Any Rum.!..!!

    Simply get tired in the evening and thoughts become a bit less clear.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  7. #33
    Join Date
    Nov 2004
    Location
    South Carolina
    Posts
    1,840
    Quote Originally Posted by jtrammel View Post
    My house is ~1300 sq ft with a 2 1/2 ton ac and it is oversized, I have to run a dehumidifier in the summer bc the ac doesn't run long enough to keep the humidity down. I'm in upstate South Carolina with a summer design of 92F. I did a load calc and it came out to 20k btus, a little over 1 1/2 tons and I know of some problems I can fix to bring the calc down a little more.
    i am in death valley cola town sc. I run a 3 ton unit and after installing new windows this year I can go to a 2 ton unit, also new doors front and back
    It is what it is unless I say differently !!!!

  8. #34
    Join Date
    Sep 2012
    Posts
    71
    Quote Originally Posted by BaldLoonie View Post
    Ignore me, the warning about the wrong furnaces is for a different thread! Shouldn't have posted after 2 shots of rum last night

    Ha! I kinda thought I mentioned that both furnaces were variable speed.

  9. #35
    Join Date
    Sep 2012
    Posts
    71
    Quote Originally Posted by dan sw fl View Post
    Definitely a 2 ton IMO (with ~20,000 BTU/Hr sensible cooling load)

    A few caveats..
    Home will be maintained at ~20'F less than outside.

    At > 78'F indoor temperature, the cooling capacity of the system actually increases.

    A dry heat is expected in mid-Missouri at > 95'F, so the air handler will operate at a higher Sensible Heat Ratio (SHR) inherently providing
    slightly larger capacity to cool the supply air.

    > 98'F in mid-Missouri should be much less than 2% of the time / significantly < 170 hours per year.
    i.e. 20 days per year for 6 hours a day.
    Worst case IMO One might expect 80'F inside for up to 15 days for 4 hours in these days of climate change.
    - use a fan for 100 hours per year if need be.-

    Those are the weather, equipment and homeowner interaction possibilities.

    So, I would go with a 2-ton because I very much like Ithe other 2,500 + cooling hours to be
    close to 40% Relative Humidity at ~76'F
    which can be achieved with run times of > 10 hours per day.
    .... without having the utility as the designated charity.

    Well I just talked to the contractor and he told me he would do anything I wanted but he said he was extremely apprehensive installing a 2 ton unit. He said he trusted his calculations that originally called for a 2.5 ton. But since the Bryant Preferred 127A doesn't come in a 2.5 ton, he bumped it up to 3 ton instead of dropping to 2 ton.

    He reasoned that since it was 2 stage it would keep the house cool no matter what kind of summer we had.

    So confusing.............

  10. #36
    Join Date
    Sep 2012
    Posts
    71
    The sales rep for the contractor just emailed me this:

    (1) Bryant up to 16.50 SEER 2.0 Tons 2 Stage Air Conditioner w/ Puron Model 127ANA024000
    (1) Bryant Vertical Cased N-Coil with Factory Installed TXV - Tin w/ Furnace Install Model CNPVP3017ATAx
    (1) Bryant 96.3% AFUE 60000 BTU Two Stage Variable Speed Gas Furnace Model 986TA42060V17
    (1) Bryant Thermidistat Programmable Digital (System) Model T6-PRH01x
    (1) Bryant $125 Mail in Rebate
    (1) $200 (power company) Incentive Included in Price for 95% Furnace
    (1) $600 (power company) Incentive Included in Price for Air Conditioner
    (1) $80 (power company) Incentive Included in Price for Motor
    (1) 10% Discount for Friends & Family Included in Price

  11. #37
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,418
    leaker2

    This is the Ask Our Pro's forum. In order to post a response here, you must have verified qualifications and have been approved by the AOP Committee. You may ask a question by starting a new thread.

    You can find the rules for posting and qualifications here.

    Additional infractions may result in loss of posting privileges.

  12. #38
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,158
    Not surprised, contractors have been forever scared of undersizing. This is why we find so many oversized units installed. A 2 ton single stage would suit you well. You need to determine the cost difference once rebates are applied.

    IMHO if utilities REALLY wanted to save peak demand they would simply limit the peak power of the unit relative to square footage of the house. Peak demand occurs on those days it's over 95 outside in most areas. EER is about the same for a 15 or 21 SEER unit. A smaller unit would reduce utilities peak demand by using less power during peak conditions then allowing the unit to do the catching up during off peak times.

    The 60K furnace is overkill for your house, a 40k is more than enough.

  13. #39
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,614
    Just have the trane guy install a 3 ton 20i with a xc 95 furnace and you will have the extra on the hot days
    We really need change now

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