If you're going to test the limits of solar-heating efficiency, you might as well do it in one of the coldest places in North America: Fairbanks, Alaska.
Bruno and Judith Grunau’s has six solar thermal panels that drink in sunlight and send the heat to a 2,500-gallon underground tank. That hot water then travels through coils underneath the floor to warm the house, while two-foot-thick walls and triple-pane windows ensure the heat stays inside. When the mercury drops below freezing (it can reach negative 30 degrees in Fairbanks), the couple relies on an ultra-efficient, wood-burning masonry heater for an extra bump.
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