What if you could design a house that on a cold day in January would stay at 70 degrees inside — without running the furnace? Or even having a furnace?It's already being done. "The builder of this passive house, Alan Gibson of the Belfast-based firm GO Logic, says he co-founded the company specifically to specialize in passive structures that would appeal to buyers seeking energy efficiency"Absolutely, along with other benefits including comfort and resilience and durability come along with it," he says. There's not a barrier of cost at that level usually," Beal says