For that you will have to get onto Your ectricity supply company, the normal one is economy 7 which is obviously seven hours, but some areas still have a midday boost and another option i can think off is option 14, wich is obviously 14 hours, but on this tarriff the heaters elements are half rated, so the normal 850 watt element is approx 425, I think there is one other tarriff so you had better check it with them to be 100% sure, Ray