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Calculating heat Loss

You should be designing for 15 degrees.


  • Rkoudelka
    Rkoudelka Member Posts: 9
    Calculating Heat Loss

    I am tryingto calculate my heat loss to determine how to heat. I have a program - pretty basic one - but there are some things I dont know how to fill out.

    1) It asks the indoor and outdoor temp. For indoor I know it is the temp I want to keep the room at - right?

    But for outdoor, is it the lowest temp I will get all winter? The average for the winter? Or some other number? The difference in heat loss/hour is huge if this number changes from 0 degress to 20 degrees, so I need to know how to interpret this.

    2) It also doesnt handle a vaulted ceiling - which I have. My ceiling goes to 16 feet. Should I do the math and figure the cubic footage, and then enter what the ceiling WOULD be to give me that cubic footage? (that makes it about 13 feet)

    3) Also, I will have a fan in the center of the room. That should help circulate heated air - it doesnt account for that, but should I compensate for it. If so , what is a fan "worth" in terms of heat loss?

    Can anyone help here?
  • R. Kalia_6
    R. Kalia_6 Member Posts: 28

    1. You will need to know the design temp for your area. That is NOT the record cold temperature, but the temperature you should design for. You may be able to find this info for your area on the web.

    2. Sounds good.

    3. Fan is worth nothing.
  • Rkoudelka
    Rkoudelka Member Posts: 9
    I forgot to mention...

    I am in the Long Island, New York area.

    So, if anyone knows what I should design for, it would be a big help.
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    What Town on Long Island?

    What town are you in? There are many different heating design temperatures depending on your location on the island. I will check Manual J on Monday to get the temperature which you should design around.
  • Rkoudelka
    Rkoudelka Member Posts: 9
    I am in...

  • Rkoudelka
    Rkoudelka Member Posts: 9
    how different could it be elsewhere on the island?

    The island isnt that big. Is it dependent on how close you are to the water?

    Just out of curiosity, where does the number come from? It must have something to do with average temps, no? Or is it totally different and just the name is misleading.

    Anyway, Im not going to argue, 15 gives me far better numbers than when I was using the program defaut of 0.

    One more thing, if the room has alot of glass (65 sq feet) south facing. Does that help with heat?
  • JimGPE_17
    JimGPE_17 Member Posts: 29

    In reality, south facing glass will cut down on your annual heating bill, but you design for the worst case - winter, lights off, nighttime, unoccupied.
  • D107
    D107 Member Posts: 1,726
    to eugene s--got a design temp for

    croton on hudson, ny 10520 (northern westchester county)?



    my guess is 11 deg F.
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    Looks Good

    White Plains is at 12 degrees, so I think you would be correct to assume a heating design temperature of 11.
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