Offering dependable performance and ease of installation, Isotemp Spa Water Heaters are backed by anoutstanding warranty: Two years on parts and a full five years on the tank.Specifically designed for marine use, Isotemp Spa Water Heaters feature a corrosion-resistant 316 stainless steel inner tank and a durable, non-corroding outer polypropylene shell.Isotherm optimizes water heating performance by locating the engine water heat exchanger as well asthe electrical immersion heating element in the lowest part of the tank where the water is coldestin order to ensure equal heating of all the water in the tank. Water inlets and outlets arespecially positioned to minimize the mixture of cold and hot water. All Spa Water Heaters include an engine water heat exchanger coil and choice of 115V or 230V operation.SPA models are offered with a choice of 12 3/8" or 15 3/8" diameters. For complete dimensions for all Spa models, see the Spa Dimensional Diagrams. For installation and maintenance, see the Spa Owner's Manual.Key FeaturesCorrosion-resistant 316 stainless steel inner tankDurable, non-corroding polypropylene outer shellDesigned to quickly heat water750W heating element