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Martin

Posted 2010-09-30 23:05 (#372)
Subject: Save electricity with immersion heaters

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The title should more accurately be, "stop wasting electricity with immersion heaters"! A common phallacy is that it's more efficient to leave the immersion heater on all the time - because then the heater doesn't have the hard work of starting from whatever the ambient temperature is.

The first reason this is wrong is that it takes almost exactly the same amount of energy to raise the temperature of water by 1 degree C, whether that's from freezing to + 1, or from 59 degrees to 60. In fact, it'll take more to go from 59 to 60, because at higher temperatures there will be more energy lost to the surroundings. And that leads to the second reason. If the hot water cylinder is constantly maintained at, say, 60 degrees, then the heat lost to the surroundings will be higher than if the temperature varies between, say 20 degrees and 60 - because then the average temperature will be lower. And if the heat lost is higher, then you must be using electricity to produce that heat.

So, if you've been leaving your immersion heater on 24/7, try just turning it on once a day - maybe for 2 hours at first, and if that still gives loads of hot water, cut back. We found that, with two of us, about 45 minutes/ day is fine. Depending on the other things you use electricity for, this could halve your usage.

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