A hot water pressure washer employs a high-pressure pump for generating a stream of high pressure fluid and a hydrodynamic heater operable for heating the fluid stream. The hydrodynamic heater includes an inlet port fluidly connectable to a fluid source and an outlet port fluidly connected to an inlet port of the high-pressure washer. An outlet port of the high-pressure washer is connectable to a handheld wand operable for discharging the fluid stream to atmosphere. A prime-mover provides rotational torque for driving the hydrodynamic heater and the high-pressure pump. An unloader valve is used to control distribution of the fluid stream discharged from the high-pressure pump. An exhaust gas recovery heat exchanger operates to transfer heat from the prime-mover exhaust gas to the fluid stream. A pre-heat tank is used to temporarily store a quantity of heated fluid for future use.