A circ pump (short for “circulating,” "circulation," or “circulator”) is a machine that keeps liquids or gasses moving in a sealed system. Typically electrically powered with very low horsepower, a circ pump might be used in a home to keep hot water close to the faucet for quick access.
When choosing and installing a circ pump, consider the heat-loss caused by moving water through pipes instead of just the boiler. It might make sense to accept a little wait time when you turn on the hot water, instead of straining your heating system 24/7 by constantly pumping water all the way through your plumbing.
To move fluids effectively, circ pumps need a system that's completely free of air, so make sure to purge your pipes when you put in a new pump. Pumps that interact with drinking water have to be made of safe materials like bronze to avoid contaminating the supply.