We have been growing heat here along with making our compost. It is a simple concept, first developed by Jean Paine in France many years ago. You basically integrate your in-floor heat with a compost pile instead of a boiler or a solar thermal panel.
We build our piles using smallish wood chips that have been used as animal bedding. The animal waste adds nitrogen to the chips causing them to compost at a higher temperature while maintaining good air flow in the pile without the need for turning. A well built and maintained pile using this system will generate 130* hot water for about six months, just make sure you keep the critters out and keep it moist during a drought.