No Furnaces but Heat Aplenty in 'Passive Houses'

DARMSTADT, Germany — From the outside, there is nothing unusual about the stylish new gray and orange row houses in the Kranichstein District, with wreaths on the doors and Christmas lights twinkling through a freezing drizzle. But these houses are part of a revolution in building design: There are no drafts, no cold tile floors, no snuggling under blankets until the furnace kicks in. There is, in fact, no furnace.