The oily rag rule of thumb and water heaters

The oily rag rule of thumb and water heaters

By Frank and Muriel Newman

This week Oily Raggers have some questions and some tips. Firstly, a question that lands some people in hot water!

Tamzin from Auckland has been trying to save power by switching off the hot water cylinder at night. “I am very keen to find out the real deal re hot water savings. I too can check daily usage online - BUT after alternating off/on for the hot water cylinder I am now using MORE power. This does not make sense to me or my provider. I have tried on at 6pm and off at 9am, but there seems to be a meter reading surge once the power is switched back on the cylinder. Anyone know what's going on? I need to get this sorted to stop wasting power when not needed.”

Good question. The answer seems to come down to a trade off between the daily cost of keeping the water in the cylinder up to temperature, and the one-off cost of bringing the cylinder back up to temperature when it is turned on again. A factor is the type of cylinder you have. Modern hot water cylinders are better insulated and have a higher thermal resistance or R-value, so they cool down at a slower rate than those with a lower R-value. In other words, the lower the R-value, the more benefit will be gained from turning off your cylinder because of the greater cost of maintaining the water temperature when it is on (but a greater benefit would be gained by wrapping an old cylinder with insulation).

One could get pretty technical about this and quote Newton’s Law of Cooling but all said and done, the Oily Rag Rule of Thumb is that if you have a modern cylinder its not likely to be worth your while turning it off unless you are heading away for about a week.

The best way to save money on hot water is to wrap cylinders that have a low R-value, set the thermostat temperature below 60 degrees, fix leaky taps and faulty valves, and use low flow shower heads.

Chris from Tirau has asked, “What can I do to make my washing smell nice without spending a fortune on conditioner?” If you have a tip or two for Chris, then please let us know via oilyrag.co.nz.

On2it from Palmerston North reckons they are on to it when it comes to saving power in the home office. “Until recently, my home office had a computer, camera, speakers, external drive, router, photo copier/scanner, telephone/fax machine, all consuming power even when turned off. (Most of the items have LED lights or displays that never go off unless the individual machine is turned off.) The power comes off one hot point which, before entering the multi-box, now has a 24hr timer set to switch on between 7am and 10pm and off outside of those hours. My power savings should now be better and if I want to work different hours, the timer override switch allows me to do this.”

Finally, for some time now we have been working away on a new edition of the book Feasting off the Smell of an Oily Rag which we first published way back in 1997 (geepers - where do the years go!). The new edition is twice as big, and we reckon 10 times better (but we would think that). Anyway, the point is this - the new edition is packed full of reader tips so if you have a moneysaving tip that you would like to see in print for the world to read forever, then please let us know. The window of opportunity is closing so get in before it closes completely. Send us your tips via oilyrag.co.nz. We would especially like to know more about how oily raggers are making the most of their backyards - what are you doing to save or make money from your "quarter-acre" paradise?
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