This isn't true. I live in MN and have a mini-split heat pump and a whole home air source heat pump that runs dual duty with my natural gas furnace. I currently

This isn't true. I live in MN and have a mini-split heat pump and a whole home air source heat pump that runs dual duty with my natural gas furnace. I currently run the cut off to switch at 20F. However both units will heat down to -20F. The mini-split struggles at that temp but the large unit still kicks out enough heat for the entire home. I also replaced two natural gas water heaters with one 80 gallon air source heat pump water heater. It can run fully heat pump but also has coils. A "high demand" mode can run both simultaneously, but 95% of the year I run it in "efficiency" mode which is purely heat pump operation. It costs about $80-90/annually so far.