The primary difference between the 5120 series and the 5000 series is that the 5120 is approved for both point of use (at the fixture) and point of source (at the water heater) applications. The 5000 series is approved point of source applications only. The 5000 series also allows for much higher outlet temperatures. Details can be found in the brochures for the 5000-Series and the 5120-Series.