Dielectric Unions

In by Mark Goodman

What Is A Dielectric Union?

Your hot water heater hooks up to your water pipes. (Well, duh.) Yeah, but that actually creates a problem. See, when you put two different metals together in the presence of an electrolyte (in this case tap water) you get a reaction called galvanic corrosion. There’s a long explanation for why this happens. The short version is, atoms from one metal break off and cling to the other metal.

Dielectric Unions Stop Galvanic Corrosion

A dielectric union is made of brass plastic and steel and is used to join steel pipes to copper.To avoid this plumbers use a special coupling called a dielectric union. It’s a coupling that acts as an electrical barrier between the two metals. One side is made of copper; the other, steel. Between the two sides, there is a non-conducting washer, usually made of rubber, which prevents the metals from interacting.

The Debate

Not everyone is a fan of using dialectric unions. Some plumbers don’t like dialectric unions because of a handful of problems that they can cause. For one, they can be a source of leaks. For another, they don’t always appear to be working. By the time the water heater needs to be replaced, often they’ve corroded, exactly what they aren’t supposed to do. Finally, plumbers don’t like them because, in light of the reasons number one and number two, they seem like a wholly unnecessary expense.

Why There Really Is No Debate

Dialectric unions are required by code. Cut-and-dry, that is it. If you or a plumber you hire is installing a new water heater, and the water pipes in your home or building are copper, you have to use them. That’s the short answer. But, for the sake of the conversation, I’ll go into a little more depth.

To the first objection, that the unions are a frequent source of leaks, I have this to say. If you’re a plumber, and your DEU’s are having frequent leaks, buy better quality parts. If you’re a DIY’er and you’re worried about this, you need to give us a call. There are things you DIY and there are things you let a professional do for you. Installing a water heater, especially when you’re working with copper, is something you leave to the professionals. (Push fittings do not make you a plumber.)

Now, about the corrosion issue: yes, DEU’s will sometimes corrode after 10+ years on the job. They shouldn’t, but if your water is hard it is an exceptionally strong electrolyte. It can overcome the barrier inside the DEU and cause galvanic corrosion. The good news is, if the DEU corroded it means your tank didn’t, and chances are you got a few more years out of your tank than you would have without the DEU. Water heaters today have built in anodes: sacrificial pieces of highly reactive metal that corrode instead of your tank. If a DEU has corroded, it’s likely been acting as another anode, giving your tank additional protection from your hard water.

Finally, the added cost and effort… it’s minimal. Times are tough and every dime people spend these days is dear, but at the end of the day, DEU’s are both a good idea and, if you live in the DC area, required by law. An extra couple of dollars on a several hundred dollar project is worth the added protection.

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