I'm as big a nerd as anyone for gadgetry and technology, but I've always had an appreciation for simpler, low-tech, more analog solutions to our woes. For example, passivhauses > solar power. With that in mind, I have to say I loved this article on masonry stoves. Despite the fact that they're huge and heavy, the basic technology seems adaptable enough to fit in many different home types. (Though you're looking at a hefty renovation, methinks.) Googling around, some companies advertise that the stoves never get hot enough to burn human skin. Or, as one company called them "huggable heaters". Very smart marketing, as my fiancée can't stop squeeing at the idea.