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This has most probably been asked before but will check before I press the 'go' button. During the colder winter months I leave the CH on from 0530 to 2230, same applies to the HW. This means there is a seven hour period when power to both services is switched off. Must say both the house and the HW seem to maintain a satisfactory balance.
The question is : Is this the most economical option or should they be left on for the full 24hours? I have heard that by switching off, both services will cool and take longer to regain the thermostat level and so negate any advantages. I keep meaning to ask the BG engineer when he does my annual service, but always forget!!
No best answer has yet been selected by waimarie. Once a best answer has been selected, it will be shown here.
For more on marking an answer as the "Best Answer", please visit our FAQ.If there were no heat loss then, once up to temperature, there would in theory be no need to input any energy. Of course, there is heat loss and so energy (electricity) must be used to replace this heat loss.
Heat loss is a function of the difference between the water temperature and the air temperature. By keeping the heater on 24 hours a day, a high temp difference is maintained between water and air. Therefore maximum heat loss occurs and this has to be replaced. By turning off the heater for a while, the temp difference decreases as the water cools. Therefore the heat loss decreases. Therefore the energy that has to be 'put back' is less.
Thus, cheaper to have it turning off (though it might be more convenient to keep it on and always have hot water).
The above is the thermal loss argument, which stands up to the laws of physics.
The conflicting argument is that gas and oil boilers are less efficient when they are in the process of heating up from cold. This does not apply to electricity which converts all its input energy into heat. So boilers cause more loss of energy if switched off for a period. I don't know the answer - I think it depends on the system design. Take meter readings over a few nights perhaps?