The 510U is well suited for residential/commercial applications such as small restaurants and beauty salons. It features a commercial grade copper heat exchanger with a thicker heat exchanger drum which is suitable for commercial applications or heavier-residential usages such as space heating or domestic recirculation systems. The design allows for a variety of installation options. Complies with Ultra-Low NOx regulations and meets the energy efficiency requirements of ASHRAE 90.1-b 1992. Easy-Link System capable up to 4 units. Multi-Link system capable up to 20 units.