Water heaters feature: Aluminum inner tanks. Hold down brackets welded to inner tank. UL or CE approved. Temperature pressure relief valve. Large 1/2-inch drain valve. Exteriors are marine galvanized steel Ignition protected. T & P drain tube included. Seaward Water Heater Selection Chart Model# | Heat Exchanger | Gallons | Width & Height | Depth | F600 | Front | 6 | 13" | 19" | S600 | Rear | 6 | 13" | 19" | F1100 | Front | 11 | 16" | 22" | S1100 | Rear | 11 | 16" | 22" | |