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Need a formula to calculate BTU loss in a pond.

  1. Jun 20, 2009 #1
    I am looking at building an ortemental pond. The pond will be 15' x 3' with an average depth of 2'. I caculated it out to 673 gallons and 45 square feet of surface area. I plan to put tropical fish in it and will have to maintain a temperature of 72F year round.
    Worst case senario would be an ambient temp of 0F.
    Based on the gallons, surface area and ambient temperature, is there a formula to calculate BTU loss and wattage of heaters to maintain the 72 degree temp?

    The initial thought is to use a heater simalar to the ones we use at work to heat our outside hydraulic units. Maybe use a home hot water heater, but I don't believe that will work.

    I plan to control pond circulation and temp with a PLC and have that end handled.

    Thank you
     
  2. jcsd
  3. Jun 20, 2009 #2
    I think your number will be about 40 watts per meter-squared per degree C, or about 180 watts per deg C for your pond, or about 7200 watts when outside temp is zero F. For better info, download this free Heat Transfer Textbook available at (11 MB file)
    http://web.mit.edu/lienhard/www/ahtt.html
    and look at page 21. If you have a circulator pump, you could heat the water as it flows through.
     
    Last edited by a moderator: Apr 24, 2017
  4. Jun 20, 2009 #3

    DaveC426913

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    Gold Member

    Having done some research on heating both pools and ponds, I've found some interesting and surprising facts.

    Something that may play an important role in your calculations is this:

    Heat loss from a body of water is only in small part due to temperature difference. By far the largest component (I think it's about 90%) of heat loss is due to evaporation. This is why, even a thin coating over a body of water such as a swimming pool - sometihn thick enough to prevent evaporation, but not thick enough to stop direct heat transfer - is sufficient to keep the water temperature up overnight.

    I grant that it is counter-productive to put any kind of film over a pond with live creatures in it. However...

    A very large factor in evaporation is wind. A body of water protected from the breeze will lose heat much slower than a body of water that is exposed to even a 5mph breeze.
     
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