Yearly oil consumption

Fortunately I still had most yearly oil orders (2012 is missing):

It looks like oil consumption is decreasing in 2014. It this because of a warm winter or the better isolation in the basement?

The Heizgradtage are usually published per calender year. Because I fill my tank in October the numbers have to be adjusted accordingly. So lets see when we plot the oil consumption and the Heizgradtage in the same chart:


Not so clear! So let's have a look at the next chart where the consumption per Heizgradtag is calculated:

The chart shows the expected ~20% energy saving in 2014.