I have an old small wood stove, and will probably be put it in my greenhouse this summer. I really don't grow in it in winter except carrots, beets and mabey some onions. It does allow me to start early and grow later in the season though as is. I also have a kerosene stove for a backup heat source, and could put that out there, but haven't yet.I watched a show on earth built homes, with the same design as your picture and diagram. It's a really low maitenance design that's really practicle and efficent. I'm pretty well set here for life now, but if I do build another place, that will be the design.