We are renting an old house. No heat. No hot water. The stairs creak and the air smells musty as we descend into the furnace room. Chris opens a cracked green door, shines a flashlight into the blackness and reaches up to pull a string cord. In the glare of a bare bulb we stand and regard The Beast in the Basement. It is silent. It has consumed a tank of oil in less than four summer months: 250 gallons at a cost of $1,099 when filled last June. It is Sunday night and the kids need to clean up before school, so we pile into the car and drive to their grandparents’ house for hot showers – pajamas in hand.

In the morning, I meet Walt, the oil guy, who feeds the beast and hands me a bill for $923. “You could throw a cat through the gap around those windows,” he tells me, talking about how to use less oil this winter.  First frost is due any day and we are motivated to winterize. Meanwhile, one of the best building scientists in the country is studying the plans for our Passive House, the super-snug, oil-free opposite of this rambling old rental.