Question: You know on wood fireplaces- you always have a key on the chimney to keep the cold air from coming in when you're not using it. Is there any way to install something like that on a gas fireplace's chimney? Answer: There are dampers for gas piping- but we run into the problem of the specific fireplace model and chimney you are using. Unless the manufacturer says it is OK to do- then you cannot install any sort of device. If there are glass doors- you can close them- and if worse comes to worse- you can make up some sort of plug (or stuff a non-combustible piece of rockwool or something similar) up toward the flue -- quite a pain if you have to do it often. <p> The above does not apply to Direct vent fireplaces in any case, since they are already sealed systems.