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Updated December 15, 2009, 10:01 pm

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Degree Days

Woman by fireplaceHelp Predict Your Energy Use

If you’re looking for ways to better predict and understand your monthly utility bill, consider learning more about degree days.  Degree days measure approximately how many degrees you need to heat or cool your home for the month and allow you to make comparisons to previous months or years. This can help you assess how much temperature fluctuations will affect your energy use.

How are Degree Days Calculated?

There are two types of degree days: cooling and heating. Each compare the current day’s average temperature to a baseline standard of 65 degrees Fahrenheit to determine the energy demands of cooling or heating your home. Days with an average temperature of 65ºF have no cooling or heating degree days.

  • Cooling degree days are used during summer months to compare the current day’s average temperature against the 65ºF standard to determine the energy demands of cooling your home through air conditioning or fans.  For example, if the current day’s high is 85ºF and the low is 65ºF, the day’s average temperature will be 75ºF.  Since 75ºF-65ºF is 10ºF, this day would have 10 cooling degree days.  Adding the degree days together for the whole month provides a way to compare previous months or years.
  • Heating degree days are used the same way during winter months to determine the energy demands of heating your home.  The 65ºF standard still is used, however, the day’s average temperature is subtracted instead of added to the standard.  For example, if the current day’s high is 30ºF and the low is 10ºF, the day’s average temperature will be 20ºF.  Since 65ºF-20ºF is 45ºF, this day would have 45 heating degree days.  Just like cooling degree days, heating degree days may be added together for the entire month to compare to previous months or years.

How Do I Get Degree Day Information?

Customers who would like to view daily heating degree day and cooling degree day information may obtain this information from the National Weather Service.

To view, visit the link below closest to your location, select “Preliminary Monthly Climate Data (CF6),” the city nearest your location, and timeframe needed.  

These reports are updated frequently and include:  daily weather statistics for the month including temperatures, precipitation, degree days, wind and sky cover.  In addition, monthly statistics such as average temperatures and departures from normal, degree days, and rainfall also are included.  Monthly reports are available for up to five years. 

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