PURPOSE:To expedite the increase in the amount of heat recovery in a heat exchanger for exhaust gas for a heating furnace and the like, by jetting the exhaust gas induced from the outlet port of the heat exchanger, thereby accelerating the flow speed in the heat exchanger. CONSTITUTION:Part of the main exhaust gas from the outlet port of the heat exchanger is induced by an inducing pipe 4 and jetted into the main exhaust gas at the inlet port of the heat exchanger from a nozzle 7 of a jetting pipe 6 by a circulating fan 5, and the flow speed is accelerated. The nozzle 7 is located at a position which is separated from the inlet port of the heat exchanger by a distance of 0.8 X flue diameter D. Thus the decrease in the temperature of the main exhaust gas due to the jetted induced gas is effectively prevented. An angle 45 deg. is provided, and the main exhaust gas is accelerated by the induced gas so that the gas hits the flue wall. It is desirable that the amount of the induced gas is about 10-20%. A control device 9 operates a regulating valve 8 based on the signals from gas flowmeters 10 and 11 and controls the flow rate of the induced gas. Thus the increase in the heat recovery amount can be expedited without modifying the heat exchanger.
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