Photo: prefabricated WeberHaus

There are now about 15,000 passive houses built around the world, with the majority in German-speaking countries and Scandinavia. It costs only about 5 to 7 percent more to build than conventional houses. Passive Houses get all the heat and hot water they need from the amount of energy that would be needed to run a hair dryer.

Decades ago, attempts at creating sealed solar-heated homes failed, because of stagnant air and mold. But new passive houses use an ingenious central ventilation system. The warm air going out passes side by side with clean, cold air coming in, exchanging heat with 90 percent efficiency.

Read No Furnaces but Heat Aplenty in ‘Passive Houses’

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