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Updated: December 2025
Installing a new water heater can look straightforward, just remove the old tank, hook up the new one, and enjoy a hot shower. However, there are a few small mistakes that can lead to massive headaches, such as premature leaks, accelerated corrosion, or safety issues that show up when you least expect them. If you’re planning a replacement, the best first step is knowing what not to do. Here are the most common water heater installation mistakes homeowners make and how to avoid them.
Incorrect Water Heater Size
Mismatching your water heater size to your household needs can cause daily frustration or unnecessary expense. If the unit is too small, you may run out of hot water during showers, laundry, or back-to-back appliance use. If it is too large, you pay more upfront and waste energy keeping extra water hot that you rarely use, which can raise utility bills over time. To avoid this, consider what are your water heater needs? How many people live in the home, how many bathrooms you have, and when hot water demand peaks during the day.
For tank water heaters, check the first-hour rating, and for tankless water heater models, confirm the required flow rate based on the fixtures you might run at once. A quick sizing assessment with a licensed plumber or installer can help you choose the right capacity and efficiency so you get consistent hot water without overspending.
Dielectric Unions
If your tank has copper or brass connectors and your pipes are made of copper, installation should be relatively easy. However, if your tank or pipes are made of galvanized steel, and you want to connect them to a copper pipe; you need to use a dielectric union. This prevents your pipes from coming into contact with one another. When they do, an electric and corrosive charge is created. This usually weakens the pipe, resulting in leaks.
What is a Dielectric Union?
A dielectric union is a fitting that lets you connect two different types of metal pipe without them touching. Inside, it has a small plastic piece that separates the metals, but still lets water flow through normally. This matters because when certain metals touch and water is present, they can start to corrode faster. The dielectric union helps slow that corrosion down, which can prevent leaks at the connection. When it’s installed correctly, it’s a simple way to help your water heater piping last longer.
Solder Connections
Don’t solder any connections near your tank. The heat might end up melting any plastic fittings. To avoid this, you should unscrew the nipples and solder on the fittings separately. Leave one connection and solder it far from the tank to avoid melting anything.
Temperature & Pressure Overflow Tube
Water heaters usually come with a temperature and pressure relief valve. This valve sometimes opens without warning and sprays hot water. Therefore, it should be connected to an overflow tube. This way, nobody will be injured when the valve opens unexpectedly. If this valve is located on top of the tank, then the overflow tube should extend to the floor. You don’t want to accidentally give your guests a scalding hot shower!
Please contact Pipe Works Services to learn more about water heater installation. We’ve been serving Union, Essex, Morris, and Somerset Counties since 2000.
