A water heater has a tank, a burner, and a heat exchanger within the tank interior volume that has three tubes. The burner exhausts gas into the first tube. The second tube is non-linear, and the third tube connects the first tube with the second tube. The cross-sectional area of the first tube is greater than the cross-sectional area of the third tube. The cross- sectional area of the third tube is greater than the cross-sectional area of the second tube.
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