Rinnai has introduced its new Duo 80 Hybrid commercial water heating system. The company says the system builds off the success of its original Demand Duo Hybrid Heating system by launching a smaller, more versatile line extension. Originally available only in a 119-gallon version, the new 80-gallon unit is designed for simple installation. Officials said its new offering is an easy upgrade for commercial replacement situations where a cost-effect solution is desired.