Close this search box.

How To Wire A Hot Water Heater: An Ultimate guide

In this step by step guide, you’ll learn how simple the process is and know how to wire a hot water heater. Therefore, there’s no need to incur extra cost on something that can turn into an exciting DIY project.
Note: This post may contain affiliate links. This means that at no cost to you, we may receive a small commission for made purchases.

After installation, the new heater can serve you up to a decade without needing a replacement. Now get ready and master this process before you get started.

Step By Step Guide For Wiring a Hot Water Heater

new water heater

Just before you start working with all the necessary wiring, you begin by collecting all the right tools and equipment for the job. It’s an essential part of this process as missing one component can make you start over.

Before you go out and purchase a water heater, get to know which one meets all your needs. Only by buying the correct heater can you get complete service. You can check online for different guides on the best home water heaters to purchase and select one that meets all your needs.

Once you finish up, next is getting rid of the old heater to make room for the new one. If you don’t uninstall the old one, then you won’t complete the process. There are several tools you need at hand before replacing the old heater with a new one. These include:

  • Screwdriver
  • Wrench
  • Pipe cutter
  • Dielectric connectors
  • Voltage testers
  • Flexible hoses
  • Sandpaper

With these tools, now you can learn how to wire a hot water heater (see also ‘Water Heater Dimensions: Finding The Right Water Heater For A Tight Space‘) in your home without needing professional assistance. Below are some steps you will follow:

1. Disconnect the water heater from the electric source

old wiring

Before you even start fiddling with the old heater, ensure there’s no electric current supply to it lest you get shocked. It’s an essential step that can result in nasty accidents if ignored.

Avoid listening to all those macho DIY guides who work on the heater without turning it off at the circuit breaker (see also ‘What Size Breaker Does A Water Heater Need?‘). Safety first must be the policy at every step when you decide to wire your electric heater.

Check using a tester if there’s any voltage to the heater once you turn the electricity off. It would be best if you do it before you touch any wires on the old heater.

2. Drain all hot water

Proceed to drain any hot water in the faucet by opening it and letting it run out. The water must keep draining until it turns cold. In this step, you empty the hot water tank without risking yourself in the process.

Remember, water in the tank is scalding hot, and safety first must be a rule you follow in this DIY project. After you feel the cold water, shut off its supply to the tank. Mostly the supply valve is at the top part of the hot water tank.

After that, drain all the cold water in the tank and leave it empty. For safety, connect a hosepipe to its draining valve and let the water run to an outside tub. Also, open the hot water valve (see also ‘How To Loosen A Corroded Water Valve‘), help drain the tank, and make the process faster.

3. Disconnect all the wiring on the old water heater

The third step on how to wire a hot water heater is removing all the electric wiring that connects to the top part of the hot water tank. Disconnecting the wires makes sure you can safely remove the old heater and check for any wires that need urgent replacement.

Again, check to see if there’s any electric supply to the heater by using a tester. At no point should you turn on the circuit breaker as you disconnect the wires? Also, check all the cables for any signs or run away current even when the breaker is off.

Moreover, label all the wires as you disconnect them to ease your work. Don’t be stamped trying to figure out which wire goes to install the new heater. Labeling is an easy way to do this, and you can even take a picture of the wiring before you start disconnecting.

4. Disconnect all the piping system

remove old piping

Check the hot water tank piping system before you disconnect it. It’s an essential step on how to wire a hot water heater. If any of the pipes used are made of copper, you might need to cut them off. Otherwise, other materials are more comfortable to disconnect from the tank.

Using a wrench, remove the pipes connected to the tank and check for any that need replacement. If all are in good condition, you can save on costs and reuse them when installing the new water heater.

5. Install the new hot water tank

After disconnecting the wires and pipes, now you can remove the old water heater safely. At this point, you can check to see what else requires replacing on the whole system before installing the new water heater (see thermostat).

Since the water heater is bulky, use a wheelbarrow or other moving equipment to remove it from the area. If too heavy, you can ask for assistance lest you injure yourself in the process of doing it alone.

After that, check the area where the tank was and clean off any dust that’s accumulated. Also, make any general repairs to the room, then proceed to replace with the new tank. Ensure you got the right tank by checking if the wiring and pipes fit as they did on the old tank. If they don’t, you might have some more work to do before wiring the new hot water heater.

You have the option of building the new water heater a platform for better installation. Use building blocks which are more efficient, affordable, and easy to install at home. Once the platform is in place, work to place the new tank on it.

As you build a platform, consider the height of the tank and the placement of wiring. Also, piping is an important part to remember.

6. Sand the copper pipes

At this step, remember the type of piping the old water heater had then prepare adequately. All copper pipes require sanding before you can use them on the new tank. Sand the pipes as much as possible until they shine.

7. Wire in the new water heater

ground wire

By now, the new hot water tank is in place. Next is how to wire a hot water heater at home. Remember, the process is simple and doesn’t require extra charges to consult a professional. Observe safety measures and follow this guide for positive results.

On the new water heater, access the wiring by removing the casing on its junction box. You’ll note a green screw ground on the heater that you need to attach the ground wire on as the first step in the wiring.

Access to wiring on the tank is by removing the junction box and removing all wires colored black and white. After that, check if you can see a knockout on the tank’s top part. Once you lock your eyes on it, proceed to break it off using a screwdriver to hold it in place. You can cut it with a pair of pliers.

It would help if you got wire connectors that you use to connect the remaining wires. It’s best to accomplish this part by twisting and access the other cables. Remember how the connections were by reading the labels or checking the pictures you took.

At this point is where the importance of taking these pictures comes alive. After that, you can close up the junction box. Still, remember to properly connect all the wires before closing up the junction box. Failure to do so might result in the heater not working correctly or working at all.

8. Attach all the pipes on the new water heater

Hot Water Heater Installation

After mastering how to wire a hot water heater, it’s time to reattach all the pipes. Water heaters require pipes for hot and cold water, which you must reattach at this step for it to function correctly.

Check all the inlets and reattach accordingly. For example, the cold water inlet should only be attached to the cold water supply pipe. The same is done to the hot water pipes. At this point, you need extra care to avoid mixing the two.

Furthermore, check the old water heater’s (see also ‘Water Heater Disposal – How To Get Rid Of Your Old Water Heater‘) piping and use the same on the new tank. If the old one had copper pies, proceed to have the same on the new one you’re installing. The previous piping is an essential guide on what is best to use on the new heater if it’s to last and serve you well.

Also, get hoses (see also ‘Best Water Heater Hose: Find Your Best Connector‘)  that are known for their flexible nature to attach heater nipples to water supplies. Flexible hoses are useful and serve you well. Also, they’re easy to replace and cost-effective. Get some plumbing tape to line the threads of the pipes before attaching the hoses.

Once the attaching is complete, check on your work before proceeding to the next step. The only way to check if piping is done correctly is to turn on the water and check for any leaks. If you spot areas that have leaks, attend to them first before you move ahead.

After you mend all the leaks, let the water flow until it fills the tank.

9. Temperature and pressure discharge valve installation

new pipes

At this point, how to wire a hot water heater doesn’t seem so complicated anymore. You’ve so far, and now you are in the final steps. Here is another crucial step that involves the discharge pipe.

Get a discharge pipe and install it on the new water heater (see also ‘How To Install A Water Heater‘) ensuring its ending is not too high from the floor. About 5 inches from the bottom is the correct measurement. The temperature and pressure pipe/valve is a crucial part of all water heaters and helps guarantee their longevity.

By correctly installing it, you know it’s safe to use the heater once it’s connected to electricity. Pressure in the hot water tank can build to dangerous levels and needs immediate release lest it explodes. It’s where the valve comes in handy to help dissipate the pressure that’s building inside the new tank.

Check that the valve you get is the correct one for your water heater. To be on the safe side, buy both from the same vendor. The guides that come with both will help shed some light on whether they’re compatible or not.

After you get the right pipe/valve for your new water heater, screw it into the tank to measure its distance to the floor. Remember, it needs to have the right height from the floor to function correctly.

When you measure, you can cut off about 4′ from the valve to attain the right measurements. You can then remove the temperature and pressure valves and cover all threads with plumbing tape for extra precaution. Plumbing tape reduces the rate of corrosion between the two metals.

Once done, replace the valve on the tank and use a wrench to fix it in place so that there are no leaks. Also, the valve has an open end that must always be facing down at this point. Since the pipe is now on the proper length, you can screw on an adapter and ensure the threads are covered by plumbing tape.

10. Switch on the power

Once you come to the end of the project, it’s time to test out the whole heating system. It’ll help you know if you’ve mastered how to wire a hot water heater or not. At this step, the electric supply for the new hot water heater is crucial.

Hot water heaters are quite specific and require a circuit that can handle 220v. Also, you need a 10/2 cable for the circuit and a circuit breaker that’s 30amp. All these must be present for this step to run smoothly and the heater to have ample electric supply.

After filling the hot water tank, turn on the electric supply on the circuit breaker and watch what happens next. Be keen to note any smoking or sounds that can indicate low wiring that needs immediate attending.

Remember never to turn on the hot water heater with a tank that’s not full of water. As a safety measure, water must fill the tank, or you risk a dry fire situation on your hands at this crucial step.

If the water is getting hot and all seems well, then you’ve successfully installed a hot water heater. If not, turn off the circuit breaker and check the wiring.

Hiring a Professional vs DIY

hiring professional

With this guide, you learn how to wire a hot water heater by yourself.

Still, this might be a cumbersome endeavor for some people, and they prefer hiring a professional. A DIY project requires ample time and a little knowledge about wiring.

If you have the time, then you can opt for the DIY. If not, don’t rush the job. It’s better to hire a professional and have the heart installed adequately. However, learning how to complete the whole process alone is a great confidence booster and a way to master some new skills at home.


Can you wire a hot water heater backwards?

Yes, you can get it with minimal effects. If the 220v heater has red and black wiring, it can be wired backwards. As much as this is possible, you must ensure you correctly wire the hot water heater to avoid water polarity issues.

How many wires on average does a water heater need?

For a 30 amp water heater, you need an 8-gauge wire. Gauge measurements vary depending on the amp.

Can I use 10 3 wire for a hot water heater?

You can use a 10 3 hot water heater but know that this has no ground whatsoever.

Does a hot water heater need a ground wire?

ground wire

Yes, a hot water heater requires a ground wire. It’s a dangerous appliance that you must ensure you follow all safety procedures to avoid accidents. At times due to low wiring, electric shorts are possible that can be life-threatening to all those who use the heater.


Learning how to wire a hot water heater at home is not as intimidating as it sounds.

However, it’s not a process to be taken lightly and requires extra caution when installing. Safety first must be your mantra at every step of the installation to avoid any mistakes that can be life-threatening.

author avatar
Charlie Hardcastle


On Key

Related Posts

Is Drano Bad for Pipes? The Truth Revealed

Note: This post may contain affiliate links. This means that at no cost to you, we may receive a small commission for made purchases. When it comes to dealing with clogged drains, many homeowners turn