Abstract: There is provided, in combination, a fireplace having a flue and a damper handle, and a fireplace flue sealing device. The fireplace flue sealing device has an inflatable bag-like member with a top portion and a bottom portion of a flexible, air impermeable material. The top portion and the bottom portion are sealed together about an outer periphery of the bag-like member for retaining pressurized air therebetween. The bag-like member has a selectively slitable, sealed area extending from the outer periphery towards the centrally located, sealed, non-inflatable area. The bag-like member is sized and shaped to sealingly engage the fireplace below the flue thereof when inflated. There is also a closable conduit communicating with the bag-like member for admitting pressurized air into the bag-like member.