What do you and your house have in common? You both need to breathe. Tightly built, energy-efficient homes don't allow for an exchange of air from inside to outside, keeping pollutants trapped indoors with you. Ceiling and attic fans, operable windows and skylights, and high-tech ventilation system filters keep pollutants from building up in your house and in your lungs. One system called Artica recycles air in the house for heating and cooling using a thermal battery made from recycled materials and no harmful coolants. The savings in energy costs? More than 90 percent. For the most extreme ventilation systems, move on up -- to a treehouse. Some cutting-edge homes are built in the treetops to catch the prevailing breezes.