A: You can have the damper closed if you have the Chimney Balloon installed up in the chimney far enough to close the damper and clear the damper hardware. But doing this is kind of like making sure to close your screen door when your heavy storm door is already closed. The screen door (damper) is not holding much back, the storm door (Chimney Balloon) is doing the bulk of the work.
There are a few things to keep in mind though if you do decide to close the damper.
1) When you inflate the Chimney Balloon make sure to install it as high above the damper as you can comfortably reach after it is snugly in place remove the long clear inflation tube from the valve handle and store the inflation tube.
2) If you try to force the damper closed and the Chimney Balloon is not high enough, it may put upward pressure on the valve section that is sealed to the Chimney Balloon portion. That is a little tough on your Chimney Balloon since it puts constant undue pressure on the valve and balloon seal.
3) The other issue is if you close your damper you may forget you installed the Chimney Balloon and just open the damper and start a fire. So make sure you put the red reminder card that is included with your Chimney Balloon in a very visible place, like on the burning grate or by the gas spigot lever.
I leave my damper open and leave the inflation tube attached so it dangles just above my head when I open the glass doors to the fireplace. With this solution, I still have no draft problem since the Chimney Balloon seals the flue tighter than my metal flapper damper ever did. – SR