With winter approaching and temperatures in the region of -10oC to -20oC expected, I want to know what the most effiecient way of heating my home is.

As I see it there are broadly two options, I can set my heating to, say, 17oC (while I`m out) and increasing to 21oC, 30 minutes before I return home. Or, I can let the house cool own more, to say 5oC through the day, using less energy, but then to return to 21oC I`ll burn more fuel.

So I repeat my question, what is the most efficient way of heating my house? I feel that this is of increased importance due to the impact of ineffiecient energy use and global warming.