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Thread: size

  1. #1
    Join Date
    Jul 2005
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    Question

    First of all I am a homeowner,however I am not trying to install anything just need info.I recently purchaced a home that needs a new furnace and ac.I have had estimates from a few companies to get opinions, not compete on price.The house is a 2000 square foot 2 story home in central Ohio.The problem I am having is sizing.One company gave an estimate for 115000 btu furnace and 3.5 ton ac.One gave me an estimate for a 92000 and 3 ton.The last one was 115000 and 4 ton.I started reading post on here and purchaced the advertized sizing program for 2 months.I plugged in all information for the whole home and the results were 69949 for heat loss and 21478 for heat gain.Knowing this what sizes should I request and how do I explain to the contractor what I did without making them mad?I just want the right size equipment.After all the research I have did on this subject I know this is important and I think these guys are just shooting from the hip on the sizing (none of the contractors measured one thing in the house they all did a walk through).Please help.

  2. #2
    Join Date
    Nov 2004
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    SW FL
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    6,386
    Originally posted by s34251e
    The house is a 2000 square foot 2 story home in central Ohio.The problem I am having is sizing.One company gave an estimate for 115000 btu furnace and 3.5 ton ac. ...
    I started reading post on here and purchaced the advertized sizing program for 2 months.

    I plugged in all information for the whole home and the results were 69949 for heat loss and 21478 for heat gain. Knowing this, what sizes should I request and how do I explain to the contractor what I did without making them mad? I just want the right size equipment.

    After all the research I have did on this subject I know this is important and I think these guys are just shooting from the hip on the sizing (none of the contractors measured one thing in the house they all did a walk through).Please help.
    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

  3. #3
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
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    34,473
    With those kind of numbers, I'd probably shoot for around 70K output on my furnace and 2.5 ton A/C. I don't like to cut the air real close, like putting 2 ton in, just because most 2 ton units are less than 24,000. I'd like a little reserve. If you like it cold, 3 ton wouldn't be so bad because it would run enough to dehumidify. Beyond a 3 ton is nuts.

    We put a 2.5 ton in a 2500+ sq ft 2 story here in Indy last month I asked the salesman if he was nuts, looked like way too little for the big east-west facing home. He inspected the job this week on a very hot, humid day. Complained about how cold they had it in there. Don't let anybody come in here and tell you so many sq ft per ton crap. It doesn't take a monster A/C to cool a well built (midwest/ohio valley type construction) home.

  4. #4
    Join Date
    Nov 2004
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    SW FL
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    Exclamation Experience

    Originally posted by s34251e
    The house is a 2000 square foot 2 story home in central Ohio.The problem I am having is sizing. One company gave an estimate for 115000 btu furnace and 3.5 ton ac. ...
    I started reading post on here and purchased the advertized sizing program for 2 months.

    I plugged in all information for the whole home and the results were 69,949 for heat loss and 21,478 for heat gain. Knowing this, what sizes should I request and how do I explain to the contractor what I did without making them mad? I just want the right size equipment.

    After all the research I have did on this subject I know this is important and I think these guys are just shooting from the hip on the sizing (none of the contractors measured one thing in the house they all did a walk through).Please help.
    R-30 Ceiling ?
    R-19 Walls ?
    Attic Temp ___ ' F
    Design Temp ___ ' F

    What is the total area ___, U-value ___
    and S.H.G.C. ___ of the windows?

    _______Glass Load = _,___ BTUh
    _____Ceiling Load = _,___ BTUh
    _______ Wall Load = _,___ BTUh
    Infiltration load = _,___ BTUh

    __ Internal Gains = _,___ BTUh
    (Lights, Computers, Kitchen, TV, ...

    ______Duct Losses = _,___ BTUh for R-___
    ______ # of people
    ______People Load = _,___ BTUh
    ____________ Total __,___ BTUh

    21,478 BTUh seems VERY, VERY Low for 2,000 Sq. Feet
    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

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,586
    80,000 90%, and 2.5 ton, by your calcs.
    Contractor locator map

    How-to-apply-for-Professional

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

  6. #6
    Join Date
    Jul 2005
    Posts
    3
    Dan I agree it sounds low.I am sorry I can not give you all the info you ask for.I used the hvac-calc program and put in all info I was ask.The isulation is r-13 for the walls and 19+ for the cieling and r-4 in ductwork.This will probably not help you, but thank you for replying.

  7. #7
    Join Date
    Nov 2004
    Location
    SW FL
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    6,386

    Question Cold

    Originally posted by BaldLoonie
    I'd probably shoot for around 70K output on my furnace and 2.5 ton A/C.

    If you like it cold, 3 ton wouldn't be so bad because it would run enough to dehumidify. Beyond a 3 ton is nuts.

    ... He inspected the job this week on a very hot, humid day.

    Complained about how cold they had it in there.
    Hopefully, it was < 80'F.
    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

  8. #8
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    5,025
    Originally posted by s34251e
    First of all I am a homeowner,however I am not trying to install anything just need info.I recently purchaced a home that needs a new furnace and ac.I have had estimates from a few companies to get opinions, not compete on price.The house is a 2000 square foot 2 story home in central Ohio.The problem I am having is sizing.One company gave an estimate for 115000 btu furnace and 3.5 ton ac.One gave me an estimate for a 92000 and 3 ton.The last one was 115000 and 4 ton.I started reading post on here and purchaced the advertized sizing program for 2 months.I plugged in all information for the whole home and the results were 69949 for heat loss and 21478 for heat gain.Knowing this what sizes should I request and how do I explain to the contractor what I did without making them mad?I just want the right size equipment.After all the research I have did on this subject I know this is important and I think these guys are just shooting from the hip on the sizing (none of the contractors measured one thing in the house they all did a walk through).Please help.
    This is how I would select the tonnage to install if it were my own home.
    Columbus, Ohio summer design: 90 dry bulb, 73 wet bulb, approx 44% relative humidity. If your heatgain is accurate, 21478 is a 1.8 ton heatload. A manual J with 15% oversizing gives you 2.07 tons, equipment selection says a 2-ton condenser with a matching "TXV metered" evaporator coil.

    I personally would go with the 2-ton; the duct system must be perfectly sized, well insulated, with NO air leaks! If it has any problems keeping up, "there are always many things you can do to reduce the heatload; think about it." I would rather have my A/C slightly undersized than oversized.

    Walked through and told you 4-ton, when the manual J, if accurate, calls for 2-ton by the approved sizing protocol.

    http://www.udarrell.com/proper_cfm_b...g_systems.html

    Is the furnace oil or gas? The large heat exchangers in most Oil furnaces can create airflow problems unless you keep the coil high enough above the furnace with usually a transition reducer.

    http://www.udarrell.com/oil-heating-airflow-test.html

  9. #9
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,386
    Originally posted by s34251e
    The house is a 2000 square foot 2 story home in central Ohio.The problem I am having is sizing.

    One company gave an estimate for 115000 btu furnace and 3.5 ton ac.

    One gave me an estimate for a 92000 and 3 ton.

    I plugged in all information for the whole home and the results were 69949 for heat loss and 21478 for heat gain.

    AT LEAST 2.5 straight or
    preferrably 2-stage 3 ton
    is needed.

    2.5 ton provides ~22,000 BTU Sensible.

    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

  10. #10
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    What design temps did you use??What city/state??



    Just call around for estimates ,insisting on a manual J,then when they do one ,they should have no promlem looking at yours ,to compare the results.Keep dialing some one there knows how.


    Try http://www.acca.org for a contractor.Or the manufacturers websites for the top dealers.

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