Raritan 20-Gallon Hot Water Heater w/Heat Exchanger - 4500w/240v [17201203]20 Gallon Hot Water Heater with Heat Exchanger 4500w 240v The "1700 Series" water heater provides hot water for galley and shower. Dense foam insulation provides better and longer heat retention than traditional fiberglass. The tank itself is protected by a 75 PSI T& P (temperature and pressure) relief valve. The cylindrical design of the tank enables it to withstand more pressure than a cube shaped tank. Heat exchanger models can be connected to the