The NRCB is the first combination boiler on the market that can simultaneously provide domestic and space heating for residential applications. These simultaneous capabilities are easy to control and especially beneficial for applications that do not store or deliver heat energy efficiently. A user can, for example, take a shower without worrying about experiencing a corresponding drop in room temperature. Another industry first is the NRCB’s use of 316L stainless steel primary and secondary heat exchangers, which have higher corrosion resistance than traditional heat exchangers for increased durability and lifespan. A third flat plate heat exchanger for domestic water heating is also made of stainless steel. It also far exceeds the toughest emissions standards. The unit’s fully modulating burner has a nitrogen-oxide emissions level of only 14 parts per million (ppm), far below the South Coast Air Quality Management District requirement of 20 ppm.