Had you done your project a few years ago, you probably wouldn't have thought much about energy efficiency. But heating fuel and electricity costs have doubled over the last two years, says Paul Scheckel, senior energy analyst at the Vermont Energy Investment Corp., a nonprofit agency charged with improving energy efficiency in the state. That means the additional cost of choosing a high-efficiency furnace, say, which might have taken 10 years of lower utility bills to recoup, could now be recovered in 5. And you'll probably be in the house long enough to earn back that entire outlay. "Plus, energy efficiency will make your house more comfortable," Scheckel says, "and it will reduce your carbon footprint."