DOES SWITCHING OFF YOUR GEYSER SAVE ELECTRICITY?

An electrical engineer says that this is a myth—and the Editor agrees with him

- ARNOLD THERON and STEVEN JONES

The expert speaks first

IT’S A popular myth that switching off your geyser saves electricity, and it's even propagated by government—but it's completely false, and it's inexcusable that a reporter does not check their facts before claiming a cited obvious (but bogus) method of saving electricity.

The fact is that in a properly-insulated geyser, the heat energy is well contained, and the only possible source of loss is the tiny amount that escapes the insulation during the day.

While the geyser is on during the day and no water is consumed, a small amount of electricity is used to replace this heat loss—the thermostat typically switches on for two minutes once every two hours (measured on my own geyser), representing a daily extra consumption of around 50 Watts per month!

Anything you do to a geyser can only save a fraction of this amount—the rest is actual energy used to provide hot water actually consumed—and you cannot do anything about that.

The fact is that by switching off the geyser, water is allowed to cool further than usual. When you switch it on again, it takes as much energy to reheat the water to its original temperature than it takes to keep it at that temperature in the first place—it's called the law of conservation of energy, and is an inviolable law of nature.

What confuses the matter, is that a small saving is actually possible because the rate of heat loss falls as the water cools—this is, however, a second-order effect that (on a daily cycle) has almost no effect.

If you leave the house for a few days, then yes—switching off will help, because once the water reaches room temperature there can no longer be any energy loss.