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  1. #1
    Join Date
    Jun 2007
    Posts
    72

    Web site or other source for homeowner to Calc heat load?

    Source for homeowner to do their own heat load calc? Thanks

  2. #2
    Join Date
    Apr 2007
    Posts
    6,285

  3. #3
    Join Date
    Oct 2006
    Location
    Emerald Coast, FL 30.1N 85.8W
    Posts
    681

    Cool rules of thumb

    Unfortunately, a lot of contractors (and I know dozens that been in the trade 30 or so years) in the southeast go by the 500 s.f/ton rule -- 700s.f/ton in the northeast.

    Another rule of thumb -- you need 400 cfm per ton cooling capacity.

    Another rule of thumb -- cooling requires 30 times your cfm volume of air.

    Another rule of thumb -- your BTU/Hr (or tonnage) requirement for heating is DOUBLE your cooling load requirement.

    So if your have a room that requires 300 cfm of air (a large living room for example), your btu requirement is 9000 btu for cooling (30 times the cfm) and heating requires 18000 btu (1.5 ton).

    This will give you an idea whether your contractor is a donkey or not, but the contractor should be able to do a calc load, unfortunately most do not.

    Quote Originally Posted by BigJon3475 View Post

  4. #4
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,323
    Quote Originally Posted by vrocrider View Post
    Source for homeowner to do their own heat load calc? Thanks
    1. Count your windows on each side of your house
    2. Insulation R-values
    3. House orientation

    Analysis to follow 14 minutes after all DWG information is provided.
    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
    Feb 2004
    Posts
    2,597
    go to the bar at the top of this page and click on HVAC Calc.

    I did it for you:

    http://hvaccomputer.com/talkref.asp

  6. #6
    Join Date
    Apr 2007
    Posts
    6,285
    Quote Originally Posted by emcoasthvacr View Post
    Unfortunately, a lot of contractors (and I know dozens that been in the trade 30 or so years) in the southeast go by the 500 s.f/ton rule -- 700s.f/ton in the northeast.

    Another rule of thumb -- you need 400 cfm per ton cooling capacity.

    Another rule of thumb -- cooling requires 30 times your cfm volume of air.

    Another rule of thumb -- your BTU/Hr (or tonnage) requirement for heating is DOUBLE your cooling load requirement.

    So if your have a room that requires 300 cfm of air (a large living room for example), your btu requirement is 9000 btu for cooling (30 times the cfm) and heating requires 18000 btu (1.5 ton).

    This will give you an idea whether your contractor is a donkey or not, but the contractor should be able to do a calc load, unfortunately most do not.
    ??

  7. #7
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,323
    Quote Originally Posted by emcoasthvacr View Post

    Unfortunately, a lot of contractors (and I know dozens that been in the trade 30 or so years)
    in the southeast go by the 500 s.f/ton rule -- 700s.f/ ton in the northeast.

    Another rule of thumb -- cooling requires 30 times your cfm volume of air.

    Another rule of thumb -- your BTU/Hr (or tonnage) requirement for heating is DOUBLE your cooling load requirement.

    This will give you an idea whether your contractor is a donkey or not, but the contractor should be able to do a calc load, unfortunately most do not.
    SF/ ton is between 333 and 1,333 depending on construction, location and orientation.

    Maybe heating is only 1/2 of cooling in FL.

    The only ton of heating that I am aware of is where that 80 year old boiler weighs 2,000 #.
    L.O.L.

    These rule of dumb will get you in trouble Most of the time!

    One needs to specifically determine the CFM per room to start a design layout.
    Last edited by dan sw fl; 06-12-2007 at 06:26 AM.
    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
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    one of the first items is to know the name of a near-by city & state
    harvest rainwater,make SHADE,R75/50/30= roof/wall/floor, use HVAC mastic,caulk all wall seams!

  9. #9
    Join Date
    Jun 2007
    Posts
    72
    1696SF 2 story over unfinished basement. 14 windows. Built 1985 with 2/4 walls, fiber wall blankets, blown in attic, masonite over polystyrene. GOOD CENTS house with storm windows. Insulated ground floor joists. Located northwest mero Atlanta. Faces north - northwest.

    Thanks.

  10. #10
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,323

    Roughly

    [QUOTE=vrocrider;1514465]1696 SF 2 story over unfinished basement.
    14 windows.
    Built 1985 with 2/4 walls, fiber wall blankets, blown in attic, masonite over polystyrene.

    GOOD CENTS house with storm windows. Insulated ground floor joists. Located northwest mero Atlanta. Faces north - northwest.[QUOTE]

    Quick Cooling Load Calculator = ~ 28,000 BTUh Sensible
    ... 3-ton A/C

    Heat Load = ~ 40,000 BTUh
    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

  11. #11
    Join Date
    Jun 2007
    Posts
    72
    Thanks.
    I have 3 ton 12SEER RUUD with matching gas single with fixed speed air handler. July, August does great but other times doesn't run enough to pull humidity down. AH is set at lowest speed to get best hu reduction and that helped alot over original setting. One year when it rained alot I got sweating registers so maybe I've slowed down too much.

    Jumped from an original 2 TON 8SEER HP that wasn't getting it done. Thought maybe I oversized too much and was looking at a 2 1/2 ton unit. AH is rated for 2 1/2T to 3T.

    After reading this board looks like VS AH might also be a choice with existing 3T.

    Comments welcomed (and needed).

    Thanks

  12. #12
    Join Date
    Jun 2007
    Location
    Phoenix, Az.
    Posts
    57
    I found a simpler Load Calculator here http://www.mrhvac.com/loadcalcshortform.htm that I used when I bought two new A/Cs a few months ago. It was simpler to use than the one at www.heat-loss-calculations.com, which I found to be buggy and difficult to use (the TBYB version).

    The short form requires extensive measured inputs and produced results that were consistent with the two originally installed Carrier units. The short form predicted that I would need a 1/2 ton more on the side of the house that had been expanded (with a lot of glass).

    BTW, I invited four different local (Phoenix, Az.) dealers to quote replacements and not one of them did a load calc.

    I ended up with a 14 SEER/12 EER Rheem (Ruud) 3 ton gas pack and a 2.5ton split system. So far, I am pleased to say that the new units are consuming about 1/3 of the peak KWH of the old ones (installed 1975). The scroll compressors are incredibly quieter.

  13. #13
    Join Date
    Jun 2007
    Posts
    72
    Thanks much JCHunter. This is what I've been looking for.

    Like you I could not get a heat loss calc. Talked to 3 or 4 guys and answer was always " I've been doing this for X years and I know what I'm doing". Wish I'd found this site or held out for someone more technical.

    Thanks again.

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