Abstract: A bent finned tube heat exchanger to transfer heat between a fluid passing through the tubes and a fluid passing around the heat exchanger, and a plate fin therefor. The plate fin has a zigzag shape defining a plurality of sharp parts and pointing alternately in opposite directions, a plurality of weakened portions, each provided between adjacent sharp parts and holes in the sharp parts aligned in two lines in the longitudinal direction of the plate fin. The heat exchanger is constructed with a plurality of the plate fins and tubes passing through the holes of the plate fins. The sharp parts are separated from each other, along the weakened portions, during bending so that the lengths of the tubes in the two lines is equalized when the heat exchanger is bent.