What Is A Dialectic Union In Plumbing?

Last Updated On November 11, 2022
what is a Dialectic Union in Plumbing

A dielectric union gets used whenever we need to connect two dissimilar types of metals or pipes. 

When certain metals contact, especially when water is involved, corrosion starts forming immediately. A dielectric union in plumbing is made with special plastic or rubber inserts to help stop this corrosion

What's In This Guide?

      When Do You Commonly Use A Dielectric Coupling Connection?

      Almost every water heater has a dialectic coupling connection. On top of the water heater are brass or aluminum fittings. 

      If we were to screw the copper water lines directly onto the brass, the water would start corroding the two dissimilar metals almost immediately. 

      Dielectric unions are made with special fittings inside to allow the water to pass by without the two metals affecting each other. 

      Do I Need Dielectric Unions?

      When two dissimilar metals touch without a dielectric union, it can lead to galvanic corrosion. Galvanic corrosion is caused by the water’s electrolytes flowing through the two metals. 

      This small electric charge is enough to eat away at the weaker metal. The non-conductive rubber gasket inside a dielectric union stops the water’s electrolytes from charging through the line.

      When Are Dielectric Fittings Required?

      Whenever two, non-similar metals must be joined in plumbing, dielectric fittings are required in almost every state. 

      While corrosion starts to form on the dialectic coupling, it stops the galvanic corrosion from building up on our expensive plumbing devices

      What to Know About a Dielectric Union for Your Water Heater

      Almost every water heater has aluminum or brass fittings extending from the top. The plumbing in our homes is copper and the water inside the plumbing lines is an electrolyte. 

      In time, the water flowing through these pipes will create a small electrical charge. 

      When two dissimilar metals are joined together, along with the electrical charge from the water, galvanic corrosion will start to form. Galvanic corrosion happens when parts of one metal cling to the other metal. 

      To stop this corrosion, a dielectric union is necessary. The dielectric union for your water heater has two purposes. 

      1. The rubber O-ring gets pinched between the two metals, preventing them from touching.
      1. The gasket inside the dielectric union is non-conductive, preventing the electrolytes in the water from ruining the water heater itself. 

      What Is The Purpose Of Dielectric Union Fittings On A Water Heater?

      We may notice that the dielectric union at your water heater has rusted. This is a good thing. If corrosion is going to form at a water heater, causing it to leak from the bottom. It’s much easier to replace the dielectric union fitting than to replace the entire water heater tank

      The plumbing connections on top of our water tank and those in our home will not be similar metals. When this is the case, we must install a dielectric union fitting.

      The list of every type of dissimilar metal is endless. From metal pipe, copper piping, iron pipe, galvanized steel pipe, stainless steel, copper tubing, and every brass nipple in between, corrosion is waiting to happen around every corner.

      Is It Required By Code?

      A dielectric union coupling, or fitting, is code and required by law in almost every state. Galvanic corrosion can start within months of brand-new installed plumbing fixtures. 

      Without using dielectric union fittings anywhere that two dissimilar metals connect, we would have to call an expensive professional plumber out to our home every few months.

      Did you know? Galvanic corrosion has become a problem everywhere in the United States. Using a dielectric union is a national code in all necessary circumstances.

      did you know dialectic union in plumbing

      Final Thoughts On Dielectric Unions.

      Dielectric union fittings are a lifesaver for homeowners. They have become more of a necessity than a convenience, with the different types of metals used in our plumbing. 

      Especially with remodels and additions,  it’s impossible to match all the same metals in a single plumbing line. Dielectric unions simply slide in between the two different types of metal so they can connect without touching. 

      We can control galvanic corrosion happening in the system by using dielectric unions. When the dielectric unions corrode, they are much cheaper and easier to replace than an entire water heater.

      FAQs On Dielectric Unions In Plumbing

      What does a dielectric union do?

      A dielectric union in plumbing stops two dissimilar metals from touching each other and corroding. The rubber gasket inside the dielectric union blocks the electrolysis process caused by the water traveling through the metal pipes.

      When should I use a dielectric union?

      Anytime that two dissimilar metals touch,  the corrosion process speeds up. It is coded in almost all 50 states to use a dielectric union and all necessary locations. 

      What is the purpose of a dielectric union on a water heater?

      Because the type of metal that residential plumbing lines are different than the incoming lines on a water heater, we have to use a dielectric union. The electrons that build up from the water traveling through the steel and copper pipes will start the corrosion process in these dissimilar metals.

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      About Plumbing Navigator

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      We write about “all things plumbing,” helping you navigate common questions, repairs, and the best plumbing products on the market.

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