Greetings: Re: Gas fired forced warm air system. Prior to the heat coming up, there is a blast of cold air coming from the room vents. This is proceeded by an ever so gentle flow of cool air. Eventually, the heat will come from the vents and warm the house. Recently, I had to access the attic and while up there, I saw this 6-8" duct pipe coming up from the furnace area into the attic space which is cold in the winter and hot in the summer. As these systems require a fresh air source, I reasoned that the duct pipe I saw was pulling the cold air from the attic space and feeding it through the duct work prior to the heat coming through if so, it poses the following question: (1) Is that pipe open all the time or is it opened and closed electronically as required.?