Thread: Use Degree Days to Compare your Utility Bills Month to Month

Have you ever tried to compare your utility bills month to month? It's impossible, right? October may be a great month, but it it was nice outside and you left the HVAC off all month. Then January is really bad, but it barely got above freezing all month. Even comparing year over year is tough because some seasons are mild and some aren't.

So how do you right-size your bills? The answer is degree days. Degree days measures how many degrees you had to heat or cool your house x the number of days in the period you're comparing. So for example, let's say it is winter, you heat your house to 65 and the average temperature for the day was 40. You effectively had to heat your house 25 degrees that day so for the day, you had 25 degree days. To get degree days for a given month, you'd do this exercise and add up all of the days in the month. To follow the example, if every day was the same temp and degree days was 25 for all 31 days of January, you'd take 25x31 which equals 775 degree days.

This would be a pain to calculate...But fortunately there is a website that does it for you. Go to Heating & Cooling Degree Days - Free Worldwide Data Calculation, find a nearby weather station and enter the period of time you'd like to lookup. The website will spit out a nice spreadsheet that you can use to compare month to month, year to year, etc.

It's not a perfect science, but it certainly helps. For example, it's helpful to know that December 09 and January '10 in Atlanta were the 2 coldest months overall in the past 3 years. That probably explains the high bills even if you did recently install new insulation or lock in a lower gas rate.

Have any experience using degree days? Post it!