You've already gone to all the trouble of felling a tree and cleaning off the branches. Who wants to spend even more time hacking it into useable chunks of firewood? That inconvenience is clearly what inspired designers Michiel Martens and Roel de Boer to create the Spruce Stove, a wood burning heater that swallows trees whole.
You'll have to make room for some supports in your living room, of course. And the size of tree is completely dependent on the size of your home. But if you've got the space, cutting down a tree should keep you supplied with free heat all winter long. [Spruce Stove via Notcot]