Fireplace flue open or closed. A fireplace damper is a little metal flap that sits inside your flue. Air can flow both ways so outside air can come into your home and the heated air from your home can escape through an open damper. The flue is essentially a channel inside the chimney the smoke is funneled through and its controlled by the damper a pair of small steel doors.
A flue directs smoke outside of a home when a fireplace is in use. Ceiling to floor metal fireplaces have a metal latch located on either side of the fireplace that allows for easy testing of the flue. No way to adjust the thing.
A throat damper is a metal door located above the firebox but below the flue pipe. When you convert a wood burning fireplace to gas you get to choose the style of your new gas logs and the pattern of the flame. See a diagram of the parts of a chimney here when the damper is closed it slows the loss of heat that would otherwise go up the chimney.
If there is a burst of cold air the flue is open. First though you choose whether to buy logs that require a vent for the gas byproducts or logs that allow you to burn them without a vent. The easiest way to tell if the fireplace flue is open is by placing a hand into a cooled fireplace and feeling for cold air.
You need to open your fireplace flue to create an efficient fire and reduce the amount of smoke and carbon dioxide in the room. It blocks off the air flow when its closed and lets air in when its open. Adjusting the damper allows you to burn a fire efficiently and safely.
Historically the term flue meant the chimney itself. This duct within your chimney includes a damper that can be opened or closed by a lever or pull chains in most instances.