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We may not be aware of it, but ordinary family homes in the U.S. and, indeed, the rest of the world are not energy-efficient. Most of their energy goes to heating and cooling, and a lot of it is wasted, as warm and cool air escape through fireplace chimneys and thin or poorly fitting windows and doors, and because of inadequate insulation. A passive house loses almost none. "Imagine a thermos," said real estate developer Brendan O'Neill. "You have insulation everywhere, and it's basically completely sealed. And so the idea is to build a house not unlike a thermos. So the windows are sealed and triple-glazed. There's insulation completely surrounding the building. We make it as airtight as possible." A 147-square-meter (1,580-square-foot) passive house, recently presented by O'Neill Development Corp. as a demonstration unit just outside Washington, was prefabricated and brought to the site in two boxes. "Once it's set and put together, it takes roughly three or four weeks to go ahead and finish the areas of drywall that weren't done, to put down carpeting if it's not in the room, to put in final touches," O'Neill said. "If everything is set in place, you put a house like this together in about three to four months." The total cost of building it was $325,000, or about 17 percent more than constructing an ordinary house. But its estimated utility bill is only around $20 monthly, or one-tenth the amount for the average house of the same size. | 
