Abstract: A regenerative heat pump includes a main compartment divided into three chambers by two reciprocable displacers. Gas in the main compartment is heated. A drive mechanism is driven by a start-up motor and is connected to the displacers to reciprocate those displacers. A flow path interconnects the chambers and exchanges heat with a heat exchanger. A secondary compartment contains a piston and communicates with the main compartment so that gas from the main compartment drives the piston. The piston is connected to the drive mechanism so that when the heat pump reaches a steady state, the start up motor can be shut-off, whereupon the piston reciprocates the displacers.