Sure but most of Maine doesn’t have natural gas service. Outside of Portland, you generally may have some gas service along Rt 1. Otherwise, at best you can get bottled propane, but you have to consume a good amount to get decent pricing. It’s usually tiered. This calculators been around for a long time and gave us a pretty reasonable estimate when we did our system.
It’s also not an either/or thing. My house (southern Maine) has oil forced hot water heat, with an older 84% efficient boiler, and a mini split. We have no natural gas service, and propane isn’t cost effective. We run the split through both shoulder seasons, and we turn the split system off when it’s consistently below freezing or oil drops below $2.00/gal (our breakeven point). The heating bill is surprisingly reasonable given the climate. As a bonus we have great AC from the split, and I don’t care what anyone says, it’s needed these days!
Are you in Maine or somewhere else?