Water Circulator units move water through a closed loop to heat, cool or hold a temperature. A pump drives the water, and a heater or chiller sets the temperature. Laboratory units connect to an instrument, such as a reactor jacket, condenser or bath, and keep the temperature steady. Heating, cooling and air-conditioning systems use circulating pumps to move water between rooms or equipment. The category lists a cooling water circulator sub-category for chilled loops. Reusing the same water in a loop also cuts water waste. Pumps and loops vary by size, so the sub-category and model decide the flow. Laboratories use water circulators for reactions, sample cooling and equipment cooling.