Does anyone have experience heating their home with the mini split ductless systems (like Mitsubishi Mr Slim) in the northeastern US? (Long Island, New York). I was told by the contractor it will provide heat even down to 4-5 degrees F. I know it's rare, but temps can get down to -0 F! Average low is around 28F, record low is -7F. So wouldn't a supplemental heating system need to be installed?

It's a 1200 sq ft home built in 1911. Single story. All ceilings are insulated, some outside walls are insulated, but not all.

Would it be recommended to just replace the gas fired forced air furnace? (40+ year old furnace, most of the existing ducts must be replaced and relocated. They are all falling apart and where not installed correctly).

THANK YOU!