A water heater can include a baffle and a slab heat exchanger with at least two rows of heat exchanger tubes, each row comprising a plurality of heat exchanger tubes. At least one of the heat exchanger tubes comprises a tube and a plurality of fins on the exterior of the tube circumscribing the tube, wherein the outer edge of each fin of the plurality of fins is bent at least at the same three areas of each fin such that the bends form at least three flat or concave areas running along the length of the heat exchanger tube.

Embodiments include various water heaters. In one example, a water heater includes a burner, an exhaust vent, a corrugated baffle having a first slit having a first length and a second slit having a second length that is less than the first length, and a heat exchanger. The heat exchanger includes a first set of heat exchanger tubes arranged in a first row, and a second set of heat exchanger tubes arranged in a second row, the second set of heat exchanger tubes having a third tube having a first angled surface and a second angled surface, where the first angled surface and the second angled surface together form a fin. The third tube can be arranged such that the fin is disposed at least partially between the first curved outer surface and the second curved outer surface.

A water heater can include a baffle and a slab heat exchanger with at least two rows of heat exchanger tubes, each row comprising a plurality of heat exchanger tubes. At least one of the heat exchanger tubes comprises a tube and a plurality of fins on the exterior of the tube circumscribing the tube, wherein the outer edge of each fin of the plurality of fins is bent at least at the same three areas of each fin such that the bends form at least three flat or concave areas running along the length of the heat exchanger tube.

Embodiments include various water heaters. In one example, a water heater includes a burner, an exhaust vent, a corrugated baffle having a first slit having a first length and a second slit having a second length that is less than the first length, and a heat exchanger. The heat exchanger includes a first set of heat exchanger tubes arranged in a first row, and a second set of heat exchanger tubes arranged in a second row, the second set of heat exchanger tubes having a third tube having a first angled surface and a second angled surface, where the first angled surface and the second angled surface together form a fin. The third tube can be arranged such that the fin is disposed at least partially between the first curved outer surface and the second curved outer surface.