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  1. #14
    Join Date
    Sep 2011
    Orlando, Fl

    Manual J


    Thanks for the great feedback and advice. Unless someone has a different perspective I think I have enough information to proceed. My profession is road contracting so I do appreciate the personal sacrifice each of you made in pulling away from your families and business to help me. I am an avid DIY but I learned along time ago if the pro makes it look easy, IT ISN'T!. Fixing my AC problems is one place where I want to hire the best and make sure they do it right. Thanks again.


  2. #15
    Join Date
    Dec 2003
    Citrus County, Florida
    I perfer to do my own load calculations as I will not trust anyone else since I will responsible if the sizing is incorrect. Every changeout should have a whole house calc done. The old unit may have been the wrong size to start with and with today's more efficient equip, you may get away with a smaller system. And yes you may have to pay for it.

  3. #16
    Join Date
    Sep 2009
    Arnold mo
    A manual J is not your first step in sizing your new a/c system. The first step is determing what can be done to improve your homes "thermal envelope". This can be done by a BPI or RESNET trained energy auditing company. The odds are very good that your existing system was oversized by as much as 1 or 2 tons, that your ductwork is undersized to accomodate your existing system, and that the only reason you havn't noticed a problem with these facts is because your home is too "leaky" (air infiltration) and your ducts are too leaky.
    It is estimated (by someone with a brain) that only 1 in 10 existing duct systems were installed in a manner that will allow newer higher efficiency systems to operate at even 80% of their rated efficiency levels.
    Forget "industry standard practices" and find a company that is re-writing those practices.
    An answer without a question is meaningless.
    Information without understanding is useless.
    You can lead a horse to water............

  4. #17
    Join Date
    Sep 2011
    great Neil Young link ...... thanks

  5. #18
    Join Date
    Nov 2004
    SW FL


    Quote Originally Posted by skibme View Post
    I found using a distance meter in addition to a tape measure helps you do it faster.Tape measure for windows and doors.
    I just keep my stride and eyes calibrated.

    __ GreAt MeaSUREment TOOLs.
    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. #19
    Join Date
    Sep 2011
    Well sh*t. Now what do I do? Ask the best contractor to do a heat loss evaluation on the site?

  7. #20
    Join Date
    Jul 2006
    Quote Originally Posted by tipsrfine View Post
    The odds are very good that your existing system was oversized by as much as 1 or 2 tons, that your ductwork is undersized to accomodate your existing system,
    My shop manager and I were just discussing this yesterday.... we were just kinda saying.... Why?? It was prompted by an estimate I was working on. Big beautiful house, big oversized equipment, way undersized duct.

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