Degree Days Analysis
The outside temperature plays a big role in how much it costs to heat or cool your home. To understand how the temperature affects your monthly heating and cooling costs you can use the standardized Degree Day Analysis when making comparisons from month to month.
Quite simply, Degree Day Analysis is the difference between the average outside temperature over a 24-hour period and a base temperature of 65 degrees. The higher the resulting number, the more energy your system will use to heat or cool your home.
For example, on December 8, 2005 the high temperature for the day was 27 degrees and the low temperature was 9 degrees, an average temperature of 18 degrees for that day. Using our base temperature of 65 we subtract 18 for a total of 47. Meaning, on December 8, 2005 there were 47 heating degree-days. On December 31, 2005 there were 20 heating degree-days. Remember the higher the number the more energy your heating system requires to heat your home. So in our above example it stands to reason that your heating system operated longer on December 8th than it did on December 31st, resulting in more electricity being used on December 8th. (Use the exact same formula to calculate cooling degree-days during summer months.)
To better illustrate this, you can look at monthly totals of heating degree-days as well. During the month of December 2005 there were a total of 949 heating degree-days, during the month of December 2004 there was a total of 811 heating degree-days. Given this information it would stand to reason that your heating system operated more in December 2005 than in December 2004 resulting in a higher electric bill for the month of December 2005.
It must be noted that other factors such as sun load or excessive infiltration due to high wind are not taken into consideration by the degree-day calculation. Additionally, things such as a home's insulation, the heating and cooling system efficiencies, thermostat settings, etc. also affect the amount of time that your heating and cooling systems will operate but Degree Day Analysis is a good standard of comparison for how hot or cold it was that month.
Below are links to information on the Degree Day Analysis for past months. This information will be updated monthly for your use.
To view these forms you will need Adobe Reader. If you do not have it, you can download it here.
Get more information on Degree Days by contacting us at 1-800-879-4056.