Georg Zielke, his wife and kids share a five-bedroom "passive house" in Darmstadt, Germany, with heating costs 90% lower than their neighbors'. Extra insulation and state-of-the-art ventilation recycle the energy from passive sources such as body heat, the sun and household appliances to warm the air. When it gets really cold, the Zielkes just turn on the TV.
The German government has thrown its weight behind the idea, guaranteeing low cost loans for people who want to build a passive house. They cost about 5% to 8% more to build than a standard one. Invented in a German-Swedish joint-venture in he early 1990s, about 10,000 have been built in Europe so far, most of them in Germany—and just three in the U.S.
This is an extended version of the article that originally appeared in TIME Magazine.