Which type of fitting is commonly used for a dielectric union in hot water heaters?

• A. Compression fitting
• B. Cast iron fitting
• C. Slip fitting
• D. Lip union

Answer: (D)

A dielectric union is specifically designed to prevent galvanic corrosion when dissimilar metals are connected, such as copper and steel piping. In the context of hot water heaters, the dielectric union serves as a crucial component, allowing the connection between the metal tank of the heater, which is often steel, and the piping that may be copper.

The correct choice highlights the fact that a lip union effectively provides the necessary separation between the dissimilar metals, utilizing insulating materials that inhibit the corrosive reaction. This allows the hot water heater to function effectively while also prolonging the life of the piping system.

While other fittings, such as compression fittings, cast iron fittings, and slip fittings, serve important roles in various plumbing applications, they do not possess the specific characteristics that dielectric unions have. Thus, they are not suitable for preventing corrosion between dissimilar metals in the context of hot water heaters.