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Degree Days

ScottI Member Posts: 4
Where did the term "Dead Men" come from?


  • ScottI
    ScottI Member Posts: 4
    Degree Days

    How does one figure Degree Days as it pertains to boiler efficiency?
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    Degree days are a measure of heating load, not efficiency.

    All degree day measurements start with a base. Here in the US, 65°F is most commonly used.

    The simplest way to calculate is take a simple average of the low and high temperature of a day. Then subtract this number from 65.

    65 - ((High Temp + Low Temp) / 2)

    Say the high temp was 60° and the low was 45°.

    60 + 45 = 105

    105 / 2 = 52.5

    65 - 52.5 = 12.5 degree days

    Ignore daily averages above 65°F.

    A somewhat more accurate way uses hourly averages. Compute the same way using high/low for the hour. Then divide by 24 for the number of hours in the day and total all 24 to get the degree days value for that day.

    Weather Underground has degree days for nearly everywhere. Enter your ZIP at the top then go down to detailed weather data. Enter a period and you'll see more options, one of which is degree days. Their calculations are based on the simple daily average at 65°F base.
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