Does everyone(anyone) agree with this? http://www.radiantdesigninstitute.com/page46.html I've been agonizing over this in piping up my Garn. I thought that ANY yellow metal (copper, brass, bronze) in contact with any iron or steel would be a problem. This says different. Wouldn't be the first time I was wrong. DIELECTRIC UNIONS Here is a very misunderstood fitting, that is seldom used properly. The problem that a dielectric union is suppose to solve is a dissimilar metal problem between steel and copper, such as a steel water tank and copper pipe. Dielectric unions in a hot water heating system are nothing but trouble and usually leak in a short time. The antifreeze, boiler additives or acid water conditions cause the gasket to deteriorate. There are better ways to handle this problem: FIRST REMEMBER THAT COPPER HAS NO PROBLEM WITH BRASS OR CAST IRON, IF YOU PUT A BRASS OR CAST IRON FITTING BETWEEN THE STEEL AND THE COPPER THE PROBLEM IS SOLVED. EVEN ON A HOT WATER TANK, A BRASS NIPPLE OUT OF THE TANK WOULD BE THE BEST CHOICE.