I did napkin math some time ago for my eastern european region: these number works with two caveats you need to get hefty government subsidy and electricity price doesn't rise.

My points are:

- one cold prolonged winter and any savings gone.

- you need to get lucky unit which doesn't need to much maintenance

- if electricity gone pray it will be back in 48 hours (where I live - to get subsidy from government you need demolish furnace)

- using solar panels to compensate when electricity lost or without taking extra electricity: minimum 15Kwh battery storage and at least 20KW panels for generating 8KW heat energy. I based on winter solstice day.