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How To Wire a Hot Water Heater: In Simple Steps

Wiring a water heater is simple enough, but you must comply with the National Electrical Codes.

Whether your new water heater was professionally installed or fitted by you, you will still need to get the wiring inspected as part of the wiring code. So, knowing how to wire a hot water heater is crucial if you want the experts to sign off on the work.

We show you that wiring a hot water heater is simple and give you hints and tips for the best results.

Key Takeaways

  • Wiring a hot water heater can be done by yourself, but must be inspected by an expert for safety.
  • Typical water heaters require three wires: black (L1), red or white (L2), and a ground wire (usually green).
  • Follow the National Electrical Code (NEC) guidelines when wiring a water heater, including using a dedicated 240V circuit and 10/2 wire.
  • Always ensure proper grounding and follow installation tips for the best results and safety.

Can You Wire a Water Heater Yourself?

You can wire a hot water heater yourself, and it’s pretty straightforward. There are caveats: you have to get the work inspected by an expert and signed off as part of the local building code.

So, while it is simple, you need a basic grasp of electrical wiring and how it works if you want your water heater up and running. If you lack the skills or confidence, it’s better to call in a pro for safety reasons.

Electric wiring in the hands of an inexperienced person could spell disaster.

240 Volt Electric Water Heater Wiring Diagram

Knowing the electrical components of your water heater helps you understand how it works. Once you’ve gained that knowledge, it is easier to carry out repairs.

L1 and L2 Wires

These wires are known as “hot” wires because they carry the load. They are alternating current, rated at 240V and 10-gauge (wire thickness rating).

L1 and L2 wires connect to your water heater and the dedicated breaker circuit on your breaker board. These wires are typically white, red, or black.

Ground Wire

The ground wire is neutral and connects to the green screw on your water heater. It prevents the pipes and water from becoming electrical conductors. Most ground wires are color-coded green.


The thermostat regulates the temperature of your heating element. It tells the element to switch on and off when it reaches the desired heat. There are two thermostats on your water heater because you have an upper and lower element.

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Heating Element

The heating element connects to your thermostat via a black and red “hot” wire. If this connection fails, the element may overheat and burn out. L-rated wires are 240V and carry the load from the thermostat to the heating element.

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The breaker is the weakest part of the system because its job is to cut the power in an emergency. The breaker switch is rated at 30 amps to handle 4500 to 5500-watt water heaters.

The breaker connects to the mains via an eight-gauge wire, rated at 240V. This is the maximum thickness for domestic systems and carries the heaviest load.

How to Wire a Hot Water Heater

Handyman adjusting gas water heater

Knowing how to install a water heater is a valuable skill. It means you can save a packet on professional costs and get the work done at your convenience.

It’s also crucial that you understand the capabilities of your water heater before you buy it. It needs to provide enough hot water for you and your family. After disconnecting the old heater and removing it, you are ready to install the new model.

Before we explain how to wire a water heater, we need to gather the correct tools.

What You’ll Need

  • Sandpaper.
  • Phillips screwdriver.
  • Voltage tester.
  • Wire strippers.
  • Concrete building blocks.
  • Wheelbarrow.

1. Position the New Water Heater

Water tanks are heavy, so if you don’t have a wheelbarrow, get someone to help you. Clean up the area where the old water tank once stood, removing debris and dust.

Erect a platform to raise the water heater off the floor. Building blocks are ideal because they require limited construction. This also helps you plan the location of the piping.

2. Sand the Copper Piping

All copper piping needs sanding before you fit the new water heater to help make a secure connection. Ensure that the copper is gleaming.

3. Wire the New Water Heater

Typically, electrical wires on water heaters are coated in flexible metal conduits. Locate the wires contained within a junction box on the top of the water heater. Remove the cover plate to expose the wires.

Take Note

Flexible wires give you some wriggle room when fitting the tank and are required in earthquake zones.

The National Electrical Code (NEC) dictates the electrical requirements for installing a water heater. You must have a dedicated 240V circuit. No other appliances can run off that circuit, and it must include a 10/2 wire, which is a non-metallic cable.

Thankfully, electrical wiring is color-coded. So, the black wire on the water heater connects to the black circuit wire. The white wire connects to the red or white wire. Use wire strippers to help you strip the wire’s sleeve if needed.

Wrap both ends of the white wire with red electrical tape. This indicates that it is a “hot wire.” 220V and 240V systems carry live loads in black, red, and white wires. Now attach the ground (green) wire to the green screw on the water heater.

4. Put the Power Back On

Go to the breaker box and flick the power back on. Use the voltage tester to check there is power to the system. It will either light up or make a sharp beeping sound.

Water Heater Installation Tips

Installing a water heater is a fairly substantial task, so finding ways to make it easier is always welcome. Here are a few tips to help you achieve your goals.

Ensure There Is Space

Water heaters must be no closer than one foot from a sidewall and at least three feet from an exterior wall unless it sits within 18 inches of another appliance.

Your professional contractor will know the exact requirements, so it’s worth seeking advice before attempting an installation.

Set the Correct Height

The expected elevation for water heaters is six feet from the floor. This helps gravity deliver a strong water flow. If you install the water heater at a lower height, it could result in low water pressure.

Fit Metal Inlet and Outlet Pipes

You can use plastic pipes, but they are less sturdy and will need replacing sooner than metal ones. Unfortunately, most modern water heaters come with plastic versions that are less resistant to temperature changes.

Take Note

Ensure that metal connectors are properly insulated to protect them against rust.

Install a Mini Circuit Breaker

Mini circuit breakers automatically cut the electrical connection to the water heater when there is a voltage change. It cuts out in an instant to protect the water heater against damage.


Can You Wire a Hot Water Heater Backward?

You can wire a water heater backward without any adverse effects. Your 220V water heater has red and black wires, making this possible. However, you still need to avoid water polarity issues.

What Happens If a Water Heater Is Wired Wrong?

It can prove fatal, especially if the system is not grounded. Electricity could travel through the pipes and water. If that happens, it causes shocks and even fatalities.

How Do You Wire a 120V Hot Water Heater?

You need to locate a nearby 12-gauge wire to connect to or install lower watt elements if the wire gauge is 14. The black wire connects to the circuit breaker, and the white wire connects to the neutral busbar.

How Many Wires Does a Water Heater Need?

A residential water heater needs three wires: a black, a white (or red), and a ground wire in 10-2 shielded cable. The white and black wires act as hot conductors, while the ground wire attaches to the green screw on the water heater.

And Finally

Knowing how to install a water heater is something every homeowner should learn. It enables you to get to grips with electrical issues and saves you money on hiring a pro.

Remember that your local building code will need to inspect your wiring to sign it off as safe. If it doesn’t comply with the National Electrical Code for voltage, amperage, and thickness gauge, it will fail.

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About the Author

Mark Weir

Mark spent 24 years working in real estate, so he knows his way around a home. He also worked with contractors and experts, advising them on issues of planning, investments, and renovations. Mark is no stranger to hands-on experience, having renovated his own home and many properties for resale. He likes nothing better than seeing a project through to completion.