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Thread: Heating formulas

  1. #1
    DIY Junior Member
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    Default Heating formulas

    I am installing a new hot water boiler replacing the existing one. Have added more space. Where do i find a calculation sheet to determine boiler size?

  2. #2
    DIY Member Lightwave's Avatar
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    You're talking about a heating boiler, right?

    What you need to do won't fit on one spreadsheet. You need to do a Manual J load calculation to find the heating needs of your space and then size the boiler as required. Manual J is very involved; the only practical way to do the calculation is with specialized software. HVAC Calc and RHVAC work well.

  3. #3
    DIY Senior Member Runs with bison's Avatar
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    Even Manual J is just an estimate.

    Have you heated your home and additional space through a winter with the existing boiler? If so and if you have a monthly record of utility usage, then you could combine that with daily average temps over the same periods to estimate actual sizing required. The usage over a given time period with given average temperature can be scaled to determine peak usage at the design temps.

  4. #4
    Jack of all trades frenchie's Avatar
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    http://www.hvaccomputer.com/hvac/tofc2.asp

    homeowner version is 50$.



    This is free, but I'm not sure how thorough/accurate it is.

    http://www.bgmsupply.com/calculateheatloss.asp



    Also very basic / simplified, but will give you a rough idea, at least:

    http://www.pprbd.org/plancheck/Heat Loss Table.pdf
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  5. #5
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    Default

    www.taco-hvac.com has a free version that is very good

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