Last night it dipped down to -20C, the furnace was running quite a bit in the afternoon so I took this chance to turn off the electricity to our electrical hot water tank and let the furnace heat our hot water.
Here you see how the tank is hooked up to the furnace. As you can see, the hot water comes out the top of the tank (since heat rises). The furnace draws from the bottom, and returns to the bottom on the other side.
Once the power was turned off to the tank we ran the dish washer, did a sink full of dishes and our daughter had her bath.