Help...Gas usage overcharge

Reed_Richards

A useful figure to know is that it takes 3.5 kWh of power to raise the temperature of 100 litres of water by 30 degrees Celsius.  Cold (mains) water temperature varies throughout the year, typically from 6 to 18 C.  Your hot water temperature is what you set it to be but 40 C is probably the minimum you would want.  Water at 60 C is too hot to touch (it would cause a second degree burn after 3 seconds).  So 30 C is probably a reasonable estimate of the average temperature through which you heat your water. 

Tallerdave

Reed_Richards said:

A useful figure to know is that it takes 3.5 kWh of power to raise the temperature of 100 litres of water by 30 degrees Celsius.  Cold (mains) water temperature varies throughout the year, typically from 6 to 18 C.  Your hot water temperature is what you set it to be but 40 C is probably the minimum you would want.  Water at 60 C is too hot to touch (it would cause a second degree burn after 3 seconds).  So 30 C is probably a reasonable estimate of the average temperature through which you heat your water. 

To show how that reflects in the real world, our 300L tank uses 50-60kWh of gas a week during summer.

Reed_Richards

The OP has a combi boiler so at least there should not be any heat losses from the tank to consider.  But if there is a long pipe run from the boiler to a tap and that tap is not in constant use then you can lose a lot of heat from water trapped in the pipe between the boiler and the tap (and waste a lot of water waiting for the tap to run hot).