Abstract: An improved heat actuated heat exchange system having conduit in a primary heating zone, a boiler in a second heating zone, and an accumulator in a third heating zone operatively connected by other conduits to a condenser, two check valves, and a heat rejector to form an hermetically sealed device containing a condensible coolant. The coolant, which is initially heated in the primary heating zone, is flashed into vapor in the boiler to produce a vapor piston for pumping heated liquid through a check valve and into a hot accumulator. Vapor pressure in the accumulator is the motive force for circulating heated coolant through the heat rejection zone, through the second check valve, and back into the primary heating zone. Check valves are utilized as pressure isolators and determine the direction of fluid flow. The system can be utilized on energy conservation devices such as solar energy systems or heat reclaim systems as the device is receptive to most heat sources with a generally uniform distribution.