We moved into a townhouse in SW Washington state that was built in 2007. The furnace in located in the attic above the second floor. While putting some decorations away in the attic, I noticed that the furnace had 2 cold air intakes. The normal one that comes from the ceiling on the second floor and the second one, a 6" diameter that came from a vent located in the roof.

My question is that there is a damper in the 6" line that at this time is closed. What is the purpose of this second air intake and the damper? Is the damper to be opened/closed during specific times of the year?

Thanks for your help in advance