Does it pay to switch off water heaters?

Steven Brockwell asked a very intriguing question in his letter to The Times (January 20). Is it more economical to switch off a water heater and switch it on only some time before use?

I used to wonder on this issue too, until I decided to carry out week-long tests that left no room for doubts. I used one of these inexpensive wattage meters that are on the market, that plug into a common wall socket, and then plugged the water heater through it.

I compared electricity consumption in kw/hrs when leaving the water heater on all day to that when switching it on only before use. The result showed a clear and significant saving of electricity consumption when switching the water heater off when not in use.

The amount saved, of course, depends on a number of factors including frequency of use, tank capacity, thermostatic level adjustments, ambient temperature and the efficiency of the insulation used inside the water heater.

The greater the temperature differences between the hot water inside the heater and that of the air in the room where the heater is installed, the greater the saving. If the insulation were 100 per cent efficient, of course, there would not be any real practical scope for all this hassle, but no insulation is that efficient.

One other thing which may be of interest in this issue - and which I tried out - was to cover up or dress the water heater with some material that decreased the loss of heat to the surroundings. I simply used two old jackets or wind-sheeters which I was about to discard, and tied these around and on top of the tank, leaving only the bottom part free, from where inlet and outlet pipes and the electrical cable are connected. The result was once again, a further clear saving on consumption of electric power.