Increasing popularity over here for outdoor wood furnaces.
Erect them in your yard, and run underground heat pipes to the house. Fuel source is usually wood, but coal or gas is an option.
I like the idea, but I would have to engineer my own. I'd build it with a solar component. In milder seasons with sunny days, solar input should be sufficient to carry you.
Then when the weather turns nippy, just fire up the wood burner, and build up a big head of heat.
You can use them for domestic hot water as well as heat.