Heat-Duct allows you to release a portion of the heat produced by the fireplace when you want to enjoy the beauty of the fire without the heat. It captures the heat from around the firebox and directs it into your home's cold air return ducting, allowing your furnace to operate much more efficiently. Instead of working at full force to heat cold air from outside the home, your furnace can work at a lower level by using the air already warmed by the fireplace.
