| 摘要 |
A gas-fired hot water heater having improved energy efficiency includes a plurality of second tubes, a plurality of first tubes which enclose the second tubes, and a cylindrical wall which encloses the first tubes. A number of fins are provided on the outer circumference of the second tubes. Cold water entering a first manifold passes downwardly in parallel fashion through the second tubes as hot gases of combustion emitted from a burner flow upwardly through the first tubes and the fins, thereby creating a highly efficient heat transfer from the hot gases to the water. An annular space between the cylindrical wall and an outer casing provides a thermal barrier to heat loss.
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