How does one heat an energy efficient home?  If you do it right, the sun does it for you.  Having lots of well-insulated south-facing windows and a deciduous tree nearby is a common trick, but that's just a beginning to how it works.  It turns out there is help available in designing a highly effective system to heat passively: PassivHaus.  They've done all the math and testing to give you specific combinations that work, within the temperate climates that exist in most of the US and Europe.

I'll still need some form of powered heat in the coldest weeks of winter, and still just to supplement the sun's effect.  To meet code I'll put in a small electric wall heater, but I shouldn't need to use it.  Instead, I'm going to build a concrete fireplace that I can load from the outside, and has a forced-air (or -water) heat exchanger to warm the living space.  A wood fireplace is cozy and pleasant in its own right, making the patio usable for more of the year.

But, is a wood fire sustainable energy?

It does put off "greenhouse gases" which sounds bad.  The trees absorbed carbon dioxide, and I'd be reversing the process.  If the wood is from managed forests, it can be a net-neutral carbon equation.  Most of the wood I'd be using for the first few years is waste wood we already have, and the only lower impact use of the wood would be mulching it for fertilizer.  I think I can live with burning the leftover wood, until I have enough solar electric capacity to use that for my heat instead.  If I need to actually acquire more wood for heat, I'll make sure it isn't a product of deforestation or wasteful industry, so I can sleep at night.