Which uses the most electricity?

Seronera

JP08 wrote: »

I'm not so sure how much cost difference it actually makes in practice. Surely any heat leaking from your hot water tank is simply keeping the chill of the house at this time of year. Assuming both are heated by the central heating, the cost of the heat from the tank will be offset by the saving from not burning so much gas to heat the house.

Used to make the same argument about incandescent light bulbs - in winter when you are using them more, they simply help to heat the room. Though in this case the heating be electricity from the bulb is a bit dearer than that from the gas central heating.

Also systems in general that are ticking over at a steady state tend to have less wear and tear, expansion and contraction etc. Would not surprise me if a steadily used central heating system lasted longer than one with extremes of on/off usage.

Whats all that got to do with heating water efficiently and economically? Well not a lot really. Some of your assumptions are just that. And how would you define 'extreme' on and off usage? Twice or three times a day is hardly extreme, but if the system is left on as you suggest it will cycle and probably end up with far more on/off cycles triggered by the room or cylinder or boiler stat than if it was switched by a programmer, so you would probably be worse off in that regard by leaving it on...unless you turned the boiler stat up to max to force it to stay on permanently and leave the house glowing like Chernobyl....just on a guess it might make the boiler last longer....which is unlikely and unproven anyway.

What you suggest does not make a lot of sense.

JP08

Seronera - "Whats all that got to do with heating water efficiently and economically?" - I'm not saying leaving things running is the most efficient way, just that the cost difference is probably a lot less than you think.

Look at it this way. Heat your tank up in the morning and (if it is a relatively modern insulated tank - ie foam sprayed on and not a crap jacket thing), switch it off, and the water will still be pretty hot to use when you get in that evening.
Keeping the water hot will use a bit more energy, but only to bring it up that margin that is lost above - which is pretty low as we've just established. Any heat that does escape the tank will be in the airing cupboard, so the temperature gradient across the foam is lower and less escapes the tank. Any heat that escapes the airing cupboard is raising the temperature of the surrounding rooms so the heating requires less to come back up to temperature. Some heat will escape the thermal envelope of the house, and that is your cost difference. Which won't be that much.

Reference the steady state thing. OK, leave the heating / hot water circuit running all day, the temperature of the water circulating won't vary that much. So minimal expansion / contraction effects on pipework / joints etc. Pump runs at a constant(ish) temperature. Boiler - not too sure, but I'd guess that a relatively steady internal temperature is preferable to sitting cold for 12 hours then burning at full roar to get everything up to temperature for an hour or so before settling to a steadyish state - wouldn't you ?