The 540H is well suited for residential/commercial applications such as small restaurants and beauty salons. Utilizing HRS35 copper alloy for the heat exchanger tubing, the 540H is also suitable for heavier-residential usages such as space heating or domestic recirculation systems. Remote control included as a standard feature. Indoor models are certified up to 10,100 ft. altitude. Thicker heat exchanger drum and utilizes HRS35 (heat-resistant) copper for the heat exchanger tubing. Provides a variety of installation options: outdoor and direct vent. Includes a pump control port, ensuring efficient operation of all circulation pumps. Complies with Ultra-Low NOx regulations and meets the energy efficiency requirements of ASHRAE 90.1b-1992. Easy-Link System capable up to 4 units. Multi-Link System capable up to 20 units.