Wood stoves are really efficient these days, hitting 70% plus, and it's Carbon Neutralish™ as a fuel source (obviously uses fossil fuels for harvest and transport and such, but that's only some percentage of the total)

I'm always amazed at the ability of our questionable 1990s wood stove to happily heat the entire house. It's a great backup heat source on days when it gets proper cold out, which is thankfully rare here.