We have been growing heat here along with 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 built our pile using smallish wood chips with in-floor heating tubing and good ventilation. A well built and maintained pile will generate heat for about two years, just make sure you keep the critters out and keep it moist during a drought.
The Golden Hoof | 3375 75th St. Boulder CO 80301 US | +1.720 900-9494