Hydronic buffer tanks, designed to reduce heat pump, chiller, or boiler short cycling, are used in systems operating below the design load condition or in systems having several low BTU cooling or heating loads calling at different times. These tanks are built with four connections. Two connections can be piped to the heat source, and two connections can be piped to the distribution system. If piped correctly, the tank can serve as both a thermal buffer volume and a hydraulic separator. The units are all stainless steel construction, and are insulated and jacketed. The tanks are available in 22, 40, 60, 80, and 115 gallon capacities, and are available with 1 ¼”, 1 ½”, or 2” NPT connections.