an energy conserving device for preventing loss of heat energy from a heater to a chimney by means of a fluid gas heat trap to choke off either chimney draft and / or heated convectional air currents lost to the chimney when the heater is off but allowing combustion gasses to vent freely to the chimney when such gasses are generated . the device also acts as a diverter for either up or down drafts from the chimney to direct them away from the heater . in another form when the device is used with a forced air type furnace , the device in addition provides heat interchange between room air and the hot gasses in the trap . this then heated air is drawn into the circulating system of the furnace adding to its temperature while lowering the temperature of the vented combustion gasses , to lessen the heat loss up the chimney .