I live in a 40 year old home in Boulder, Colorado. It has a high efficiency natural gas furnace that's one year old. We bought the place after this was installed. I've found an 8 inch round air supply duct coming directly in from outside that empties near the base of the floor. I noticed the lower level of the house was very cold and found a huge draft of cold air coming down this pipe. The house has original windows and plenty of cracks around doors. Is this air supply pipe really necessary? What else could be done to keep the cold air out?