Most of us live in the moment when it comes to energy. The latest electricity or natural gas bill we received often influences our attitude and actions. Sometimes, we forget how much our energy bills are dependent on the weather. Yet, understanding the impact of weather on our energy usage helps us anticipate and budget for these costs.
It seems that every part of the country likes to claim a special status when it comes to the weather. The superlatives include everything from having the hottest summers to the coldest winters. Some cities brag about having four distinct seasons while others tout having moderate temperatures all year long. Nevertheless, how do we compare weather in a way that helps us understand differences in energy usage? The answer lies in the concept of degree days.
Degree days are a measure of how much you need to heat or cool your home. This allows you to make comparisons to previous months or years or to other regions of the country. In this way, it increases our understanding of why our energy bills fluctuate from season to season.
Calculating Degree Days
There are two types of degree days. One is cooling degree days (CDD) while the other is heating degree days (HDD). Each compares the average daily temperature to a baseline of 65° F. Every degree the average daily temperature is below 65° F is a HDD. Conversely, every degree the average daily temperature is higher than 65° F is a CDD.
The first thing that hits you is that these are not necessarily good assumptions. For most of us, there is a range of temperatures during which we are neither heating nor cooling our homes. We are reasonably comfortable so the heater and air conditioner get a rest. Like all standards, 65° F is simply a common benchmark for comparison.
Tale of Two Cities
Let’s take a look at two cities from a degree day perspective. Houston, Texas and Boston, Massachusetts are both large cities located on or near the coast. The chart below portrays degree day information for each city.
As expected, Houston is cooling city and Boston is a heating city. An interesting item to note is that Houston averages more than twice as many CDD than HDD. For Boston, the ratio is opposite and more striking. Boston has more than six times as many HDD than CDD.
Home Energy Implications
It is helpful to look at home energy in terms of heating and cooling. Homes rely on a variety of fuels for heating. The three main heating fuels are electricity, natural gas, and fuel oil. Massachusetts consumers rely heavily on natural gas and fuel oil with only 10% of their homes using electric heat. In contrast, about half of all Texas homes use electric heat. However, unlike heating, electricity is pretty much the only fuel used for home cooling throughout the country.
As shown in the graphs above, cooling is not a major focus for Bostonians. Furthermore, home heating in Massachusetts is decidedly non-electric. Houston residents, on the other hand, use a lot of electricity throughout the year with their air conditioners and electric heat pumps. Therefore, an average Houston home should have a much higher electricity bill than its Boston counterpart. Actually, the difference is less than you might expect it to be.
The U.S. Energy Information Administration reports that the annual Texas home electricity bill is only 64% higher than the average residential bill in Boston. Perhaps 64% seems like a big difference. However, keep in mind that Texas homes use about twice as much electricity as Massachusetts homes. The difference is attributable to the electricity rates. Massachusetts has low usage and higher rates. Texas has higher usage and lower rates. In either case, there is a financial incentive to shop for the best available electric rates. Regardless of where you live, it makes sense to pay attention to how the weather affects your energy bill.