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  1. #14
    Join Date
    Jan 2010
    Location
    Athens GA
    Posts
    1,234
    Load calc s have only come into their own in the last 10-15 years.
    Before that there were no calcs done ande if a contractor wanted to soundv hi tech he counted alum siding as insulation.
    Insulation codes came into being in the 1970's.
    Before calcs furnaces were sized by the "bettor to be too big than too small method"
    Non contractors swimply would not believe the number of 100,000-120,000 btu units that we collectly have torn out of homes and replaced them with 45-50,000 furnaces.
    I had one job where two janitrol 120.000 furnaces were twined and I took the both out and replaced them both with one 60m hi eff furnace.
    A/cs were all sized by rule of thumbs like one ton per 500 sq feet,or 600 sq feet.
    I don't know for a fact but I can guess THAT THERE HAS NEVER BEEN A LOAD CALC DONE ON YOUR HOUSE. As far as insulation is concerned you probably have the minimum requirements done because it was 1989.
    To the fellow that laughed at asking for the blueprints,I used to ask.Not everyone has their blue prints and you would be surprised at how many do.If I had them the load calc just went so much quicker and smoother.I'd say it cut at least an hour off the time required.

  2. #15
    Join Date
    Jun 2009
    Location
    Albuquerque NM
    Posts
    2,484
    Quote Originally Posted by REP View Post
    Load calc s have only come into their own in the last 10-15 years.
    Before that there were no calcs done ande if a contractor wanted to soundv hi tech he counted alum siding as insulation.
    Insulation codes came into being in the 1970's.
    Before calcs furnaces were sized by the "bettor to be too big than too small method"
    Non contractors swimply would not believe the number of 100,000-120,000 btu units that we collectly have torn out of homes and replaced them with 45-50,000 furnaces.
    I had one job where two janitrol 120.000 furnaces were twined and I took the both out and replaced them both with one 60m hi eff furnace.
    A/cs were all sized by rule of thumbs like one ton per 500 sq feet,or 600 sq feet.
    Reminds me of one contractor I had at my house. I asked if their company used Manual J calculations, and his reply was "We used to do that a few years ago, but every system we did that way was undersized and we had to tear them all out and replace them all."


  3. #16
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,717
    Quote Originally Posted by garya505 View Post
    Reminds me of one contractor I had at my house. I asked if their company used Manual J calculations, and his reply was "We used to do that a few years ago, but every system we did that way was undersized and we had to tear them all out and replace them all."


    Probably one of those contractors that thought all houses were tight construction.

    Or. Just said that as an excuse not to do one.
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  4. #17
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    I am a homeowner and in my experience of 3 load calcs for my house (2 of which I did using Hvac-Calc), they are unlikely to differ much unless somebody makes a goof. Remember this is a model, and garbage in = garbage out.

    Evidently the job of doing a Manual J is worth $XXX at the going rate of professional labor. Better to pay that than to size wrong. Lots of people do cut a corner and just size according to what was installed before. It's not the worst thing to do but sometimes people are unhappy with the results, for example the new system might have inferior humidity removal because of a different design. In my case a Manual J told me downsizing was appropriate and that has to help humidity removal.

    Best of luck -- Pstu

  5. #18
    Join Date
    Jun 2010
    Location
    Houston, TX
    Posts
    178
    I've been asked for blueprints too.. or get charged double for it...
    I've got all the rooms sizes and orientation, isn't that enough for blueprints??
    What exactly are blueprints needed for in Manual J if not for sizes?


    Quote Originally Posted by REP View Post
    To the fellow that laughed at asking for the blueprints,I used to ask.Not everyone has their blue prints and you would be surprised at how many do.If I had them the load calc just went so much quicker and smoother.I'd say it cut at least an hour off the time required.

  6. #19
    Join Date
    Feb 2012
    Location
    Lynn, Mass
    Posts
    134
    Quote Originally Posted by crayx4 View Post
    I've been asked for blueprints too.. or get charged double for it...
    I've got all the rooms sizes and orientation, isn't that enough for blueprints??
    What exactly are blueprints needed for in Manual J if not for sizes?
    If one or two of your measurements is off and the house doesn't heat/cool properly, who would you expect to fix it by pulling out the system and installing a different one? If I am asked to install a system and you had all the info, i'd at least want to doublecheck at your expense in order to be confident in my install. If that was a problem, then you would sign a piece of paper that states "The system being installed is the correct size for the measurements that were given to the installer, whether this is the size system I need for this actual house or not is not the liability of the installer and I take FULL responsibility for the sizes handed to him. After reading that, would you rather sign that paper, or pay a man to measure your house and write stuff down and calculate for 2-3hrs?

  7. #20
    Join Date
    Feb 2012
    Location
    Lynn, Mass
    Posts
    134
    This AINT rocket science, but it is science nonetheless!!!

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