Green Tips from England!
I had a brief look around your green lifestyle page... (further to the Winter Energy Efficiency article...)
Chimneys are a source of much heat loss, unused chimneys should be sealed with a chimney balloon.
Open fires are on average 15%efficient, wasting 85% of the energy, stoves however, especially the smoke-free woodstoves (I use 2 'Clearview' British built stoves) are in excess of 85% thermally efficient and enable you to use renewables.
It is true that keeping your flue clean will give a more efficient burn.Yours, John Cossham, York, UK