Water Heaters 101 > Pipe Nipples

What you'll find on this page: All water heaters need something to connect them to the plumbing. That's a pipe nipple, and they come in different sizes, diameters and metals.

Pipe nipples are connectors. They are threaded on both ends. One end goes in the tank, while the other connects to some sort of plumbing. That can be solid copper, or copper or stainless flex, or even PVC. Nipples can be made of galvanized steel, PEX-lined steel or brass.

There are several examples in the photo to the right. There is a big 1 and 1/2-inch PEX-lined galvanized nipple that is used in commercial water heaters. The others are 3/4-inch for residential tanks.

The one upright is another PEX-lined galvanized; the two right behind it are plain galvanized steel. You'll notice that they look rusty. There is even more rust to be found inside them. The ones shown below left appear to be completely clogged with rust, but oftentimes, a little water will still flow through them.

One of the troubles with using plain galvanized nipples is that they are often bright and shiny on the outside but very rusty on the inside, and if you try to remove one, it may snap.

The one between the rusty ones is made of brass. It won't rust, and for that reason, plumbers like them. But it will react with steel, and water heaters are made of steel.

When steel and brass come in contact in water, the steel rapidly rusts. That won't happen to the tank because the anode protects it, but it speeds up anode consumption and sometimes causes side effects. The optimal pipe nipple to use is PEX-lined galvanized steel. The outside won't react with the tank and the inside won't react with anything. such as that from which the water heater is made of. Plain galvanized nipples are the cheapest. Brass and plastic-lined cost about the same.

One more little interesting fact: if you use a brass nipple to connect a recirc return to the tank, there is a good chance that it will react with the water heater anode and get plugged with corrosion byproduct. One reason for this is water is constantly flowing through it, It's better to use a PEX-lined steel nipple.

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