I had an oil delivery today, heating oil that is. It was 900 litres and got the tank nearly full, but not quite. That’s the problem with my oil tank, you don’t ever really know how much is in it, and only if you fill it full (according to the delivery man’s pump) do you know how much is in there.
But allowing for these uncertainties, I reckon that I’ve used between 30 and 50% less fuel than last year, taking account of the milder weather. Factors in this include: new boiler in November 2010; switching to a possibly more efficient burner regime of having the boiler on at a lower temperature for the whole day (I have the thermostat set and 17 or 18; it gives me a constant summer’s day sort of temperature) and also the additional use of my wood burning stoves once or twice a week since late October.
I’ve probably got enough data now to have a stab at calibrating my tank measurements. I measure the depth of oil in the tank, but the tank is a cylinder of unknown diameter on its side, so the rate of reduction in oil level is not necessarily related to the amount of fuel burnt. What I do recognise is once the level goes below 20 inches, it starts dropping quickly. I may have enough data now to have a stab at a chart to approximate how much usage I have left in the tank for a given depth. It’ll keep me entertained doing that!