The changing colors of trees in fall signals that soon we'll need to turn on the heat. It makes me realize how valuable the sun can be for heating our houses, saving energy and reducing bills — the flip side of designing a house for living without air conditioning . Designs for passive solar heating work on two principles: maximizing the amount of sunlight that hits a house's interiors in the cold months and storing that heat so it is released inside after the sun goes down. This ideabook looks at a few houses to see ways to design for the benefit of each.