Some bright spark once suggested not using the heating at all is cheapest, but the question is really whether you want warmth or not and when. We have the heating on at all times and thermostatically controlled (even in summer at which time it simply correctly decides it is not needed and hibernates), 21 degrees while we are awake, 18 when sleeping. The house has four generously sized bedrooms, two public rooms, kitchen, two bathrooms - very high ceilings in half of that. Annual cost �500 (gas, not in the UK's warmest area either), well worth it we reckon. We have good insulation and draught free, k-glazed windows.