I've been planning to buy a small dishwasher for my kitchen for some time. Here in Australia most washing mashines come with hot and cold connections to use the main house heater which is more efficient than lots of small heaters everywhere. Makes sense.

Most dishwashers, however, have a single hose usually to be connected to the cold supply but pretty much all models I've investigated can also run on the hot supply only. The one I'm interested in doesn't exactly say what it would like but its hottest wash temperature is 65°C.

Knowing that my hot water is quite hot, I tried to figure out exactly how hot it really is. Turns out my storage water heater (one of the ubiquitous Rheem 80l things) says "thermostat max setting 70°" on the outside, and a peek at the electrical innards tells me that it has a piece-of-shit thermostat which is fixed to 69.5°C. Thanks, fellas! TI, manufacturer of said crap, even boast that it is "Tamper-proof: temperatures are factory set to customer position"...

Well, no longer: the newer Rheem things come with a Robertshaw adjustable thermostat, and so does mine - since 30 minutes ago :-)


Which leaves me pondering how high I should set it. 70° costs quite some money and is stupidly unsafe; I've hurt myself more than once despite well knowing the situation. But the pipes are cold (and uninsulated: welcome to Oz!), you turn on the hot water, hold hands under same, cold cold cold HOT! FUCK!

On the other hand, AS/NZS 3500.4.2 says 60°C minimum for hot water storage to kill legionella bacteria off. A newer version of the standard then requires nonlinear physics: no more than 50°C at the outlets, so the plumbers are happy because they can sell you costly mixing valves. Yay!

On the gripping hand, 60°+ still very much hurts. For example, the USA and Canada have a 50°C maximum for storage heaters because of the scald problem, and even hereabouts some governments have common sense approaches: 1992-94 the NSW government ran studies and a biggish campaign on the problem, and their final report shows evidence that the legionella problem isn't really that big: after a lot of political stuff, it says on page 17 that studies show 50°C to be enough to keep the bacteria at bay.

So I've chosen a middle ground, and set the thermostat around the 56°C mark.

[ published on Thu 23.03.2006 20:05 | filed in interests/au | ]
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