One Response to Q: What are heating degree days and how do they relate to utility spend?

  1. Kent McDonald says:

    A: A heating degree day (HDD) is a measurement used to translate each day’s temperature to the energy demands of furnaces, boilers, and other heating systems. Heating degree days can be used to compare the current winter to past winters. It can also be used to compare the cold in one part of the country with another.

    For example, heating degree days can be used to help explain variances to prior years’ natural gas consumption (or other heating source such as electricity or fuel oil). This is especially helpful if you are able to “componentize” your consumption/usage data from your rate and total cost data, which can be done using NWP’s UtilitySmart or a similar service. A sister organization of the National Weather Service keeps records of HDDs per month (and per week) at the national, regional, state, and major city level, which you can find here.

    Nerdy bonus info: You can calculate heating degree days by subtracting a day’s average temperature from 65. For example, if the day’s high is 35°F and the day’s low is 25°F, the day’s average is 30°F. So, 65 minus 30 = 35 HDD. Another handy link is (national/regional/state) Temperature Rank. For example, you may have heard that the Winter of 2011-2012 was “unseasonably warm.” The national temperature rank for March 2012 was 118. A rank of 100 is considered average or normal, which means that March 2012 was 18% warmer than normal, creating an expectation that your energy consumption should have been 18% lower than in an average year.

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