High-efficiency condensing water heater

A water heater comprising:

• a water storage tank configured to store water to be heated, the water storage tank having a top wall, a bottom wall, and a side wall extending between the top wall and the bottom wall, the side wall including a curved portion;
• a heat exchanger configured to transfer heat to water stored in the water storage tank, the heat exchanger including a first pass flue extending between the bottom wall of the water storage tank and the top wall of the water storage tank, and a plurality of second pass flues coupled to receive combustion gases from the first pass flue, each of the plurality of second pass flues exiting the water storage tank through the side wall of the water storage tank;
• and
• an exhaust manifold associated with the side wall of the water storage tank, the exhaust manifold including a gasket defining inlets for receiving each of the second pass flues, and a cover defining an outlet from the exhaust manifold;
• wherein the outlet defined by the cover is oriented to extend in a direction radially outward from the cover.