Alberta

From what I understand, you only use a heat pump until the outside temp reaches 0c, maybe -5c. Below that you go back to using the furnace.

One of the big draws of a heat pump is pumping heat "out" of the house in summer instead of running an air conditioner. If you get a chilly spring night, the heat pump should maintain the house temp without running the furnace. Supposedly it does both of these more economically than running an AC and furnace, but it is not a replacement for a furnace.