Abstract: A heating apparatus including a circulation system for hydraulic fluid, a pump for pumping the fluid, a windmill for driving the pump, an adjustable pressure responsive relief valve for restricting the flow of hydraulic fluid in the circulation system and establishing therein an adjustable fluid pressure reduction, a sensor responsive to the wind velocity encountered by the windmill, a valve control mechanism responsive to the sensor for automatically adjusting the fluid pressure reduction provided by the relief valve and a heat exchanger for removing heat from the hydraulic fluid. The work performed by the wind in pumping the hydraulic fluid through the relief valve is converted directly into heat that is conveyed to the heat exchanger for conversion into a useful form. By adjusting the relief valve to establish increasing pressure reductions with increasing wind velocity, the system optimizes the rate of wind energy utilization.