Rheem has 4 models of Tankless Water Heaters.If you have 1 bathroom, a Rheem Tankless RTG-42 series water heater should provide an ample supply of continuous hot water.  If your home has 1-2 bathrooms, you should consider a Rheem  Tankless RTG-53 series water heater. For up to 3 bathroom homes, the larger Rheem Tankless RTG-74 series water heater should be selected.  For homes with more than 3 bathrooms, large volume demands for hot water, or hot water circulating systems, you should choose our Rheem Tankless GT-199 heavy-duty water heater.  In some applications, our GT199 and RTG-74  rheem tankless water heater can be  linked together in a manifold configuration to meet the higher volume demands for continuous hot water. In fact, up to 20  models can be linked together to work as one water heating system where only one remote control and manifold controller are required – a Rheem Tankless Exclusive Feature