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What Are Degree Days and How Do They Impact Your West Texas Home?

Degree days tell a clear story of energy consumption.You may have noticed a spot on your utility bill that informs you of the number of "degree days" for a given month or even for an entire year. If you’re like most homeowners, you probably asked yourself, "What are degree days?" Then you forgot about it. But understanding degree days can save you money on energy bills, reduce the amount of fuel you use year-round and make you and your family more comfortable in your west Texas home. 

What Are Degree Days?

Heating degree days (HDD) and cooling degree days (CDD) are measuring sticks you can use to evaluate energy efficiency improvements around your home. Use them to compare energy efficiency over time. 

Heating degree days are the difference between the average temperature of a day and 65 degrees. Add the day’s low and high temperatures, then divide by two. That’s the day’s average. Subtract that from 65 degrees. The result is that day’s number of heating degree days.

In west Texas, suppose a cold winter day has a low of 14 and a high of 30. Add those two temperatures and divide by two: the day’s average temperature is 22 degrees. Subtract 22 from 65; that cold winter’s day has 33 heating degree days.

Cooling degree days are similar, but this time 65 degrees is subtracted from the average daily temperature. Suppose a hot summer day has a low of 80 degrees and a high of 98. The average temperature for the day is 89, which is 24 degrees above our benchmark. So that day has 24 cooling degree days.  

Why 65 Degrees?

Heating engineers set 65 degrees because people and equipment add their own heat in winter and require cooling in summer. Your efficient programmable thermostat may be set for 68 degrees in winter, but some of the heat in your house comes from your family and their activities, such as appliance and electronics use. The benchmark makes for convenient and generally accurate calculations. 

Saving Money

A better answer to the question, "What are degree days?" They're historical data that can save you money. You may have been told that adding insulation in the attic will save on energy costs, but how can you be sure you'll recoup your costs? By looking at historical data from degree days, you can measure your return on any investment you make in your home. 

Imagine that in the summer of 2013 you spent $1,000 on energy improvements, including:

For December 2013, your energy bill still climbed compared to a year earlier. Now you worry that the improvements were of no help. You need unbiased data that account for changes in weather from one time (before the improvements) to another (after energy efficient upgrades). 

Degree day data is readily available for free on the Internet for every region of the country. Enter your locality and time frame, and you get a spreadsheet of information to download. 

December 2012, the Lubbock area had 711 degree days. December 2013, by contrast, had 858 degree days—an increase of nearly 121 percent. Why? December 2013 was colder—and for more days—than December 2012. Naturally, your heating system worked more for the colder month. 

Now look again at your total energy bill from both months. Consider not just the electricity you've used, but any fuel used for your furnace or boiler. If your home’s energy costs for the colder month increased by less than the degree day percentage, you know you saved energy and money. 

Cooling Works, Too

Cooling degree days work in the same way, allowing you to track improvement in energy efficiency in summer months. When your central air conditioner is working less, you use less electricity and save money.  

In our Lubbock example, July 2012 had 528 degree days, while July 2013 had 435, a decrease of around 18 percent. You should have seen your electricity usage go down by approximately that amount. If it did, or went down by significantly more, you know your energy-saving steps were effective. Remember, the upfront investment will save you money every heating and cooling season. 

For additional help answering the question, "What are degree days?" or using data to guide energy-saving investments around your west Texas home, contact us to help you locate a contractor in your area.

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