Abstract

A vapor generator for use in, for example, an absorption type water cooler or heater. The vapor generator having a burner section and a boiler section, the boiler section being constituted by an outer casing, an inner casing disposed in the outer casing, and a multiplicity of solution tubes attached in rows to the inner surfaces of wall of the inner casing so as to extend substantially vertically. The interior of the tubes is in communication with a space accommodating a medium to be heated and defined between the inner casing and outer casing. A multiplicity of fins are attached to the inner surfaces of walls of the inner casing in the area around the flame formed by the burner section so as to increase the rate of heat transfer to the medium in the above-mentioned space from the gas in the combustion chamber. The axis of each of the solution tubes in a second row is offset from the line which extends in parallel with the flow of gas from the midst of the gap between two adjacent solution pipes in a first row located upstream from the second row as viewed in the direction of flow of gas, so that overheating of the central portion of each solution tube in the second row is avoided advantageously.