[ Home ] [ Up ] [ Fuel Bills ] [ Growing Vegetables ]

No surprise that when the weather is colder, your fuel bills go up. But when you keep records of mean temperatures AND you have your previous gas bills, you can go one step further...

My quarterly gas bill shows the energy used in kWh, so I can plot a graph of gas used per day against the mean daily temperature over the 3 month period covered by each gas bill. If you count the dots you'll see I've got the necessary information for the last 8 years (one dot represents 3 months data, so 4 dots per year). 

The dots appear to be in 4 clusters of 8  - the top cluster is the Dec-Mar quarter (the coldest bit of the year), the next one down is Sep-Dec, the next one down Mar-Jun, and the bottom one Jun-Sep (the warmest).

So, yes, the gas used goes down as mean outside temperature rises, and Excel provides a linear best fit with a good correlation.  When the outside mean temperature gets to 17.5 degrees, the only gas used would be for heating water, which is small compared with that used for heating the house! Our mean January temperature has not gone below 4.4 degrees over these 8 years, so the graph seems to have broadly the right characteristics. 

The scatter can probably be accounted for heating being on for longer when I'm in the house more, less when I'm out, and that the inevitable occasional "estimated gas bills" will differ slightly from gas actually used, and because I pay an averaged out monthly amount to them anyway there was little incentive to bother telling them it was slightly wrong!

The conclusion is that gas energy used per day in kWh is approximately 188 - (10.7 x mean temperature).

Translating this into an averaged out cost of gas per day plotted against mean temperature, I got the following graph. This is worked out based on today's gas prices, not the slowly increasing price over the last 8 years, which would have distorted the findings.

No surprise that when the weather is colder, your fuel bills go up!