I have a new 100,000 btu natural gas furnace in a room about 170 sq feet with a 7 ft ceiling. I recently put a solid door to the room to reduce (and it has substantially) noise from the forced air furnace.
Unfortunately in order for the burners to ignite obviously they require air (oxygen). I have been told that with this solid door closed the room is too sealed off for enough oxygen to keep the burners going when they come on. I was told to put a vent to the outside with a pipe to within 2 feet of the burners to provide them with air from the outside.