Power Consumption of Dishwashers

Dishwashers using Hot Water

Supplying dishwashers with hot water reduces energy consumption significantly.

A no-frills dishwasher from China with an Energy Star Rating of 2 and a Water Star Rating of 2.5 used the following

Cold Water Inlet test:
Water inlet temp: 20C +-2C
0.971 kWh per cycle
15.58 litres of water

Hot Water Inlet Test:
Water inlet temp: 60C +-2C
0.377 kWh per cycle
15.68 litres of water

Which equates to approx 354 kWh per year (cold water inlet) vs 137 kWh per year (hot water inlet) at 7 runs per week on the 'Normal Cycle'.

If you are connected to the electricity grid, then at 25c per kWh you would pay:

  • 354 kWh per year ~ $88.50
  • 137 kWh per year ~ $34.25

A difference of approx. $54.25 per year. Very significant when you add up the cost of running all your appliances. Obviously, the cost of heating the water externally was not taken into account. Should you heat your water with gas or electricity, using hot water for dish washing may even increase the total cost. However, if you have a solar hot water system, you can save a fair bit.

A Fisher & Paykel Dishdraw dishwasher used 380Wh per normal load on 'Eco' setting with a maximum power draw of 1200 Watts. This test did not state which water inlet was used, but if the test results of the above dishwasher infer that hot water was used.

Drying Cycle in Dishwashers

As far as drying cycles go, all units have a cycle that has to pass the Australian Standards, this is usually the program such as Normal, or Normal Eco 45C or the like. Part of the Australian Standards is a dry test.

From observation most of the machines have a dry cycle which is a 30 minute period or so. This drying is done by the final rinse temperature.

During the final rinse the water is heated to a temp. of probably minimum of 45 Celsius, normally 50 C, and then the machine will often leave that water in the machine to use as heat, and that somehow dries the dishes, there are some machines that have a fan in the front door to circulate the steam out of the machine, but it is rare to find a machine that drains the water before the drying cycle starts.

So from that you can gather that there are currently not many dishwashers that heat the air to dry the dishes. (there may have been some older dishwashers that did heat the air, this also melted the plastics). Therefore unless you take off the final rinse (generally 2 rinses after main wash) you won't really gain much by trying to eliminate the drying cycle.

There are now machines with economy drying, and also economy heating during wash. But this is reflected on the Energy star rating (if tested in the economy mode). Some machines may have a program that doesn't include drying the dishes, but they are normally just rinsing cycles etc.

Also if you look in the instruction manual it will describe the cycle of the different machines.

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