Boxtops and bookbinder have sussed it: Unless you have significant draughts and/or poor insulation (rov1200's scenario) then letting the temperature plummet uncontrollably and then reheating furiously is the more expensive regime. The reality of this is exactly the same as timing the engine run on a car and then switching it off for a period (and coasting at ever slower speed), then restarting and accelerating at full throttle, etc. in a repeating cycle - all in order to travel from A to B. The most fuel efficient way to drive is at a steady pace, no sharp decelelation or acceleration - i.e. the central heating equivalent is keeping the heating on constantly and controlled by a thermostat all the time (small drops, small rises). This regime can be operated at a lower temperature (15 instead of 20 for example) in order to save money (but you will feel chilly). If saving money irrespective of the consequences on heat/cold then of course not using the heating at all is cheapest the same way as cutting food bills is achieved by not eating. Reduce the volume of accommodation to be heated if you like, but be aware that condensation will almost certainly occur where there is no heating. The maximum heating reduction is achieved by resorting to only heating individual pieces of furniture (electric blanket, etc.). The least fuel efficient way, regardless of the level aimed for or achieved, is using gas fires which put somewhere between 50 and 70% of the heat straight up the chimney. Bottled gas heaters are extremely likely to give rise to condensation due to all the flue gases (including the moisture generated) being within the heated space, quite apart from the unhealthy and potentially dangerous situation. Note that if you allow cross ventilation through the house (doors ajar) while heating only a room or two then you will be shifting moisture from the heated area to the unheated area where the air will cool and the moisture will be dumped (condensation). Better to close a