Abstract: A retrofit heat transfer unit, including: a housing for the retrofit unit, including inlet and outlet ports for water and refrigerant; a water pump, in fluid communication with the water inlet port, the water pump adapted to pump water from a water source; a heat exchanger, in fluid communication with the water pump, the water outlet port, the refrigerant inlet port and the refrigerant outlet port; and a thermostat, configured to measure a temperature of the pumped water and activate the water pump when the water is below a predefined low temperature and cease to pump when water is above a predefined high temperature. The retrofit unit is also adapted to receive heated refrigerant fluid from an air conditioner and direct the refrigerant through the heat exchanger and direct the pumped water into the heat exchanger so that the refrigerant heats the water and the water cools the refrigerant.