Degree Days

Weather is the biggest factor affecting electric bills. The hotter it is, the more energy it takes to cool a building. Conversely, the colder it is, the more energy it takes to warm the space.

But how do you measure that?

Utilities and the government use a metric called Cooling Degree Days (CDD) and Heating Degree Days (HDD) to measure how weather affects electricity usage. This allows an apples-to-apples comparison of one day, week, month or season compared to another.

This same calculation could help CoServ Members and Customers understand why their own usage might be higher for a particular billing period, especially during the hottest summer months or coldest winter months.

For example, you receive a high electric bill after the first month of summer so you adjust your habits, raise the thermostat and keep a closer eye on your daily SmartHub usage alerts to cut back on costs. Then, despite your efforts, your usage is even higher on your next bill.

That means the average daily temperature was hotter than the previous month, which means the Cooling Degree Days would be higher.

It starts with the baseline temperature of 65 degrees outside, using the assumption that homes won't need air conditioning or heating at that temperature.

The higher or lower the temperature is from 65 degrees, the harder your air conditioning or heater will have to work to maintain the temperature in the home.

The first step is to find the average temperature for the day. If the value is above 65 degrees, you will subtract 65 from it to find the CDD.

Then, to find the total number of CDD or HDD for a set period of time, you can add the Cooling or Heating Degree Days together for each and you can start to get a picture for why usage is so high for a certain period.

For example, August 2023 was an especially hot month with a total of 872 Cooling Degree Days in Dallas-Fort Worth. Since 2000, that's the second highest total for Cooling Degree Days for a month behind only August 2011, which was 887, according to the National Weather Service.

Looking at Heating Degree Days, if you go back to February 2021 when Winter Storm Uri descended on Texas, the Heating Degree Days totaled 660. Compare that to the same period in 2022 when the Heating Degree Days totaled 526 and you'll see why electricity or natural gas (depending on the type of heater you have) would be higher.

Heating Degree Days