Heat exchanger for pressure washer

A high pressure washer comprising a heat exchanger for heating a cleaning fluid, and a dispenser for dispensing heated cleaning fluid under pressure onto a surface to clean it, said heat exchanger comprising

• a casing having first and second end walls and a tubular sidewall extending therebetween along a central longitudinal axis,
• a tubular heat shield inside the casing having a first end adjacent the first end wall of the casing and a second end spaced from the second end wall of the casing to define a gap therebetween, said heat shield having an inner surface defining a combustion chamber within the casing, and an outer surface,
• a burner adjacent the first end wall of the casing for discharging flames and hot combustion gases into the combustion chamber,
• an annular space between the outer surface of the heat shield and the casing,
• a heating coil inside the casing extending longitudinally with respect to the casing for containing cleaning fluid to be heated, said heating coil comprising a length of unfinned tubing disposed in the gap between the second end of the heat shield and the second end wall of the casing, and a length of finned tubing in said annular space between the heat shield and the casing,
• said burner being operable to emit flame and hot gases of combustion into said combustion chamber in a direction toward said second end wall, said heat shield serving to protect the finned tubing by directing the hot gases of combustion for contact first with said unfinned tubing, resulting in cooling of the gases, followed by contact with the finned tubing in said annular space, thereby enhancing the heat transfer between the gases and the fluid contained within the heating coil.