PURPOSE: To obtain a combustion gas heat exchanger unit in which acid concentration is prevented to produce no adhering matter and a manufacturing method therefor.

CONSTITUTION: A combustion gas peat exchanger unit comprises a square enclosure 1 having a pyramidal side wall 2 and a PTFE bellows type tube 4 interposed between two supporting plates 5 is contained in the enclosure 1. Two supporting plates define a gas chamber 6 into which white heat gas flows through a hole 7 made in the lower surface and from which low temperature gas flows out through another hole 8 made in the upper surface. Air to be heated flows into a heat exchanger unit through a hole 9 made in one pyramidal side wall. The air passes through the gas chamber via the bellows tube and flows out through a second hole 10 made in the opposite pyramidal side wall while being heated.