Update February 2012 : You can now get degree-days for anywhere on the planet calculated for free by kWIQly
Given a stream of dry-bulb temperatures (normal Celsius or Fahrenheit ignoring wind-chill) - We can write down how we calculate heating degree-days for any particular balance-temperature really easily:
Instructions ...
For each regular temperature measurement in a day write down 0 if
temperature is above balance-temperature. Otherwise write down the difference between balance-temperature and air-temperature. Degree days is the average of all the numbers written down.
Here is a really simple worked example....
| Time | Air Temperature | Degree-Load for 15.5 Balance |
| 12:00 AM | 12 | 3.5 |
| 01:00 AM | 9 | 6.5 |
| 02:00 AM | 8 | 7.5 |
| 03:00 AM | 8 | 7.5 |
| 04:00 AM | 7 | 8.5 |
| 05:00 AM | 6 | 9.5 |
| 06:00 AM | 5 | 10.5 |
| 07:00 AM | 4.5 | 11 |
| 08:00 AM | 6 | 9.5 |
| 09:00 AM | 7 | 8.5 |
| 10:00 AM | 8 | 7.5 |
| 11:00 AM | 12 | 3.5 |
| 12:00 PM | 15 | 0.5 |
| 01:00 PM | 16.5 | 0 |
| 02:00 PM | 15.5 | 0 |
| 03:00 PM | 14 | 1.5 |
| 04:00 PM | 13 | 2.5 |
| 05:00 PM | 12.5 | 3 |
| 06:00 PM | 11 | 4.5 |
| 07:00 PM | 10 | 5.5 |
| 08:00 PM | 10.5 | 5 |
| 09:00 PM | 9 | 6.5 |
| 10:00 PM | 8 | 7.5 |
| 11:00 PM | 8.5 | 7 |
| Average | 5.71 |
So here we see a day with 5.71 "Degree-Days" of load - It is simply the area in "degree-days" under the horizontal balance temperature line - Shown here in Red - The lower the Temperature (Green) - The bigger the red area relative to the balance or "on-set of heating" line
