Abstract: A gas-fired boiler plant comprises a burner bed (10) extending over a flat surface and heat exchanger pipes (61, 62) arranged above the burner bed (10), parallel to the said surface. The heat exchanger tubes (61, 62) comprise pipes (63, 64) equipped with a plurality of flat ribs (65, 65a . . . , 66, 66a . . . ) which extend substantially radially from the said pipes and which are provided in spaced arrangement over the length of the said heat exchanger pipes (61, 62). The ribs are provided with bent-off portions (70, 71, 72, 73, 74, 75). The hot flue gases (82) rising from the burner bed (10) flow through the gaps (84, 84a) formed between the said ribs (65, 65a . . . , 66, 66a . . . ) and pipes (63, 65).