I have a 10 gallon Rheem water heater that has what looks like factory installed dielectric 3/4 inch nipples on the hot and cold connections. I have tried to get info about the need for dielectric unions in addition to the factory installed nipples. So far I have not had a definite answer from Rheem or anyone else. I have already installed the heater with copper directly to the nipples but I could put dielectric unions on it without much trouble. Obviously I don't want to use them if they are not needed. Does anyone have any experience with the Rheem with factory installed pipe nipples?