The Rheos smart boiler / water heater is a breakthrough in commercial heating system design. Now, for the first time, engineers and heating contractors can choose a single high-efficiency, low-cost system for commercial installations requiring up to 2.4 million BTU/hour. Plus, the Rheos features the highest density and smallest footprint available, so it takes up far less floor space. In fact, it's so compact, it can fit through a standard 3'-0" doorway.