Ceiling dampers are used to limit the passage of heat in fire resistive floor-ceiling or roof-ceiling assemblies where ducts or other penetrations are made only through the ceiling membrane of the fire resistive assembly. Fire resistive ceiling membranes are part of floor-ceiling or roof-ceiling assemblies that have been evaluated for their fire resistive capabilities. A ceiling damper is subjected to severe testing to prove the ability to prevent the transfer of heat in concentration from a fire area to the structure above. A definite funnel effect is created at openings in rated ceiling assemblies and the ceiling damper is specific to protection against this phenomenon.