Raritan 20-Gallon Hot Water Heater w/o Heat Exchanger - 120v [172001]1700 Series Water Heater 120v 20 Gallon W O Engine Heat Exchanger 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