Agree with suburbanmd about washers that won't temper hot water. This seems to be the way He washers in the US control energy usage, buy mixing cold with hot water, so the booster may not work with that unless you can manually pour hot water into the machine or do one of those y connector things mentioned in another thread.
The heater on my W1986 tends to cycle on and off for the 105F and 120F washes, more so in the winter since my machine is in an unheated basement. For the 140F and 190F washes it will take hot water in and sometimes mix it with cold. After a few minutes of tumbling you can hear the heater circuit clunk on. It will continue to clunk on and off until about halfway into the wash and then the heater will remain on and turn off some minutes before the cool down water runs in. The tumbling continues with the cooled water for a minute or so and then the wash water is pumped out. It is at the end stages of the 190F wash when you will hear the water fizzling during the pauses.
In the winter the heater comes on when doing a cold wash right at the beginning but only once, so it isn't used throughout the entire wash.
If I shine a flashlight through the holes in the bottom of the tub I can see the heaters sitting below the tub; there are two of them. On the door label it says Heaters: 2 X 1300Watt so I guess that is their rating.
For the normal wash cycles it takes about 41 minutes at temps of 105F and 120F, about 48 minutes at 140F, and 51 minutes at 190F. The Extended option increases the time for everything; wash, rinses, and spins. Normal works for most loads, Extended with cold water prewash for heavily soiled whites.
