Degree Days Can Mean Unexpected Electricity Consumption

A little math goes a long way to understanding how much a heating or cooling system has to run


Understanding the gap between outdoor temperatures and a targeted indoor temperature can help consumers manage energy consumption and spending.

Heating Degree Days and Cooling Degree Days are concepts and calculations that propel some engineers, facility managers and electricity generators straight to their whiteboards. They’re also significant factors in the amount of electricity every home and business uses, so a little math can go a long way in managing electricity use and spending.

At their hearts, heating degree days (HDDs) and cooling degree days (CDDs) measure the gap between hourly outdoor temperatures and a targeted indoor temperature.

For example, if the average temperature between midnight and 1 a.m. is 35 degrees and the targeted indoor temperature is 65, there is a 30-degree difference. The people who measure these kinds of things divide those 30 degrees by 24 to get 1.25 HDDs for that hour. They do the same thing for each hour of the day and then add them all up for the day’s total HDDs or CDDs. ( uses 65 as a base for its report, though 68 also is a common base and 68 is the winter thermostat setting that recommends.)

The more HDDs or CDDs for the day, the more a heating or cooling system has to run. Longer run-times mean more electricity consumption and sometimes larger-than-anticipated invoices. They also mean more maintenance and potentially shorter equipment lifespans, which are additional reasons engineers and facility managers follow degree days so closely.

“Consumers often compare the bottom line of their invoices from month-to-month or year-to-year,” said Scott Harrison, director of engineering and innovation for TXU Energy. “Weather is one of the biggest factors in electricity consumption and we know it changes all of the time.

“Take January for example,” Scott added. “Many of us in North Texas forgot how cold it was at the beginning of January because we were wearing shorts and T-shirts at the unseasonably warm start of February. The recent wintry spell in late February also generated a significant number of HDDs, which affected how much electricity homes and businesses were using.”

In addition to comparing details of the weather using degree days, Scott said consumers can:

  • Compare the number of days included in the meter read cycle for each invoice they are reviewing.
  • Log in to their TXU Energy MyAccount or TXU Energy MyEnergy DashboardSM to see estimated spending for the current month and review when they are using electricity.
  • Set up alerts so they know when their usage appears headed toward an invoice that’s more than any level they want.

“Knowing the various factors that affect electricity consumption is the first step in managing consumption and spending,” he said.

More Pov


TCEH Corp., Parent Company for Luminant and TXU Energy, Emerges from Chapter 11 as a Competitive, Well-Capitalized Company

News Release   TCEH Corp., Parent Company for Luminant and TXU Energy, Emerges from Chapter 11 as a Competitive, Well-Capitalized Company     *** Energy Industry Veteran Curt Morgan Formally Named CEO   *** Restructuring Eliminates More Than $33 Billion in Debt   *** Benefits from Low Leverage Relative to Peer Group   *** Company […]

Job One Profiles: Razen Thomas

Razen Thomas is proud to be Powering Texas and proud of the hard work and innovation that she sees from her colleagues every day at Oak Grove Power Plant. As support manager, Razen makes sure everyone has the tools, equipment and processes to do their jobs safely and effectively. Watch this month’s Job One Profile […]

A Soaring Success

An abundance of wildlife, including numerous bald eagles, call Luminant’s sites and reclaimed land home. When Liberty Mine’s resident bald eagle pair returns this fall, they’ll find a few home renovations – most notably, a new nest location. The eagles’ nest was recently moved away from mining activities to a new location on company property […]