If the sun arcs to 35 degrees above the horizon at noon on December 21 and your living room windows face south, how much do you pay for heat that month? The question might sound hopelessly inscrutable, but not to Washington, D.C.-based designer and remodeler Alan Abrams, CPBD (certified professional building designer), who carried out such calculations when he was designing this green addition in Silver Spring, Md. More
