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How To Wire Water Heater Thermostats

Note: This post may contain affiliate links. This means that at no cost to you, we may receive a small commission for made purchases.

Water heaters are great appliances. They save energy and reduce our carbon footprint. But they also require regular maintenance.

If you want to get the most out of your water heater, you should regularly check its performance and ensure that it operates at peak efficiency.

A properly working water heater provides hot water 24/7. The temperature of the water depends on the type of water heater you have.

For example, gas or electric water heaters produce warm water, whereas tankless water heaters provide instant hot water.

You can easily install a new water heater by yourself. All you need is a wrench, some tools, and a little bit of time.

In this article, we’ll show you how to wire a water heater, as well as teach you some important information about them that you’ll need to know as a homeowner.

Thermostats – What Are They?

The thermostat is an electronic device that regulates the temperature in your home. It’s usually located near the furnace or boiler, but it may be installed elsewhere if there’s no room for one next to the appliance.

How To Wire Water Heater Thermostats

There are two types of thermostats: upper thermostats and lower thermostats. You will need both of these thermostats to wire into your water heater.

Both of these thermostats are interchangeable with other brands and therefore it doesn’t matter which one you use.

Similarly, you will not need to replace a thermostat with the same brand as you previously used if you don’t want to.

Don’t worry too much about which type of thermostat you want to purchase, as they are all similar. Here is a list of thermostats that we recommend:

Upper Thermostats

  • Apcom 110-160 degrees
  • Therm-o-disc 90-150 degrees

Lower Thermostats

  • Apcom 110-160 degrees
  • Therm-o-disc 90-150 degrees

Residential Vs Commercial Thermostats

A residential thermostat is not rated for water higher than 160 degrees, in both pressure and temperature.

This is why you need to purchase a thermostat that is lower than this maximum degree allowance.

Here are some of the best residential thermostats on the market:

  • Rheem UV11698
  • Rheem SP11698
  • Camco 08163
  • Aprom / 110-160°

On the other hand, commercial thermostats can withstand higher temperatures.

For these tanks, you should get a thermostat rated between 120 and 180 degrees.

If you’re looking at the latter end of this spectrum, bear in mind that 180 degree thermostats are only suitable for commercial water heaters rated for this high of a temperature.

Here are some of the best thermostats rated for commercial use and therefore higher water temperatures:

  • Rheem SP8293 / 170°
  • Camco 08304 / 180°
  • Rheem SP8295 / 170°
  • Camco 08314 / 180°

Choosing The Correct Thermostat For You

While all thermostats are interchangable, it is still important that you opt for the correct one to avoid disappointment.

The last thing you want to do is purchase a thermostat for commercial use instead of residential, only for you to install it and it creates further issues that you have to pay more for!

It can be overwhelming looking at the market, as there are so many thermostats to choose from!

However, remember that all thermostats can be swapped for each other, meaning that they are all basically the same.

Here’s an example.

Example Number 1: Low Density Thermostats

Both the Apcom Low Density thermostat and the Therm-o-disc Low Density kit come with the following: two low density 240V 4500W elements, upper and lower thermostats.

The former is 110-160 degrees while the latter is 90-150 degrees.

The difference in temperature might make you think that they are not interchangeable, but they are. This is because they are both suitable for residential water heaters rather than commercial.

Example Number 2: High Density Thermostats

Similarly with the low density thermostats, the high density thermostats are also interchangeable.

For example, the Apcom high density kit and the Therm-o-disc high density kit both come with the following: two high density 240V 4500W elements, upper and lower thermostats.

Again, the temperature ranges are different: 110-160 degrees for the Apcom kit and 90-150 degrees for the Therm-o-stat kit.

However, they are still interchangeable as they are both rated for residential use.

Should You Choose Low Or High Density Thermostats?

Low density thermostats are generally better suited for residential applications where the tank will not be used very often or at times when the tank is not being used.

They are also cheaper, which makes them ideal for smaller budgets.

High density thermostats are usually better suited for commercial applications where the tank will be used frequently and/or during peak hours.

These thermostats are also more expensive, making them unsuitable for small budgets.

Lower density applications could last longer if you have hard water, so this is definitely another factor to consider when choosing which thermostat to go for.

If you live in an area with soft water, you might be able to use a high density element without risking its lifetime.

Bear in mind that newer water heaters typically come with high density elements. However, as we have already mentioned, you don’t necessarily need to purchase another high density one when replacing it.

Different Types Of Water Heater Thermostats

There are a few different water heater thermostat types, and the one that you opt for will alter how you wire it.

How To Wire Water Heater Thermostats

Some are much easier to wire than others, but you should choose the correct one according to your personal situation.

Let’s take a look at the different water heater thermostats that you could choose from.

Non Simultaneous Thermostats

Non-simultaneous thermostats are never on at the same time. One is always in the on position while the other is always in the off position.

This is true unless the water heater has been wired for another reason, which would be down to the owner’s discretion.

As both the upper and lower thermostats are never in the on position at the same time, it is called a non-simultaneous thermostat.

To adjust the temperature of one of these thermostats, simply use a screwdriver to alter it to your desired range. The residential range of temperature should be between 90 and 150 degrees Fahrenheit.

The average water heater thermostat temperature is set to 120 degrees in most households.

How To Wire These Thermostats

From the 240V water heater, you’re going to need to wire L1 and L2 to the upper thermostat.

L4 will come from the upper thermostat to the lower element.
T2 and T4 will run from the upper thermostat. T2 will attach to the upper element and T4 will travel down to the lower thermostat.

The lower thermostat and lower element should also be wired together, as should the upper thermostat and upper element.

Non Simultaneous Thermostats Controlling Two Water Heaters

Some households find that they require two water heaters and therefore need the thermostat to control both of them at the same time.

The good news is that you can do this by wiring them together. This is a form of simultaneous wiring!

Adding another water heater to your home can allow you to never run out of hot water, even in the busiest times.

This means that everyone will be able to have their showers, the chores will get done, and the heating can remain on throughout the day without anything running cold.

However, there are some rules that come with having two or more water tanks on your property.

These include:

  • The first heater needs to be at temperature before power can be sent to the next water heater.
  • The second heater might not get to the temperature that you’ve set the thermostat to in time for the first to turn on again. This will leave you with lukewarm water in the second water heater.

The second rule might be down to poor insulation or very cold water filling the water tanks.

You might be able to fix these issues to prevent the second scenario from occuring again.

Foam insulation is an excellent option if your water heater is not heating up quickly enough. However, it might also require long drill bits from the center of the tank to allow for the wires.

This can allow heat to escape, so make sure that the thermostat is not placed near these as it could lead to the temperature being misread.

How Does Connecting Two Water Heaters With One Thermostat Work?

240V water heaters involve two wires coming from the circuit breaker – both are already hot and one will be tested at 120V to the ground.

As the thermostat opens and closes it allows the heat from the second wire to get to the element. The heat will then turn the element to an on or off position.

Now the thermostat will either be hot on T2 or T4 (sometimes labeled 2 and 4), but it will never be hot on both at the same time.

The lower thermostat will be on the first water heater, and this will spark it to do one of two things:

  • Send more power to the first water heater’s lower element, or
  • Send power to the second water heater.

However, the second water heater will not turn to the on position, and therefore not start warming up, until the first water heater is off.

This will only get to the off position once the water has come up to temperature.

Once the first water heater gets to temperature it will move to the off position and then the second water heater will be able to use all of the 240V power to heat up itself.

How To Wire Two Water Heaters To Their Thermostats

Start with a 10 gauge wire connected to the breaker. This will connect between the two heaters and their corresponding thermostats.

Both circuits from the 10 gauge wire will be the same for both thermostat.

The first water heater will require two upper thermostats and the second will require one upper thermostat and one lower thermostat.

L1 will attach to the breaker and L3 will come from the 10 gauge wire. Both will attach to the first upper thermostat.

L4 will come from the first upper thermostat to the lower element.
T2 and T4 will run from the first upper thermostat.

T2 will attach to the upper element and T4 will travel down to the second upper thermostat.

The first upper thermostat and upper element should also be wired together, as should the second upper thermostat and lower element.

Moving onto the second water heater now, L1 will run from the second upper thermostat from the first water heater to the upper thermostat for the second water heater.

L3 will come from the 10 gauge wire from the breaker.

L4 will connect the upper thermostat with the lower element.

T2 and T4 will both come from the upper thermostat. T2 will reach the upper element while T4 connects to the lower thermostat.

The lower thermostat and lower element should also be wired together, as should the upper thermostat and upper element.

Whirlpool Energy Electronic Thermostats

Newer water heaters are seeing an increase in how many are coming with electronic thermostats rather than traditional thermostats.

Some believe that they are more convenient for the user as well as preventing people from having to replace them themselves.

However, this is not the best news for people who like to save money and conduct their own DIY. Electronic thermostats are higher in cost and require specific pieces as replacements.

Remember when we said that all thermostats were interchangeable? This is true for all but electronic ones.

So, opting for an electronic thermostat is going to cost you more money in the long run.

Some speculate that this is a marketing tactic to prevent people from being able to purchase generic spare parts, as now you will have to go to the manufacturer of your thermostat to get replacements.

But what if they’ve been discontinued?

Simultaneous Thermostats

We’ve talked alot about non-simultaneous thermostats, but what about the alternative? Simultaneous water heater thermostats mean that both of them operate independently from one another.

They are used for water heaters that need more energy than just one thermostat can offer. This might be due to its large size or continuous high demand.

You can replace the lower thermostat with an ECO protected thermostat if you’d prefer, and each thermostat is wired separately.

Each element will draw around 4500 to 5500 watts of power, so you’ll need each thermostat to be wired to a different circuit breaker.

This means that you’ll likely need more wire than you would if you were to be using non-simultaneous thermostats.

How To Wire These Thermostats

Simultaneous wiring will mean that you have two thermostats within one water heater, but they will not be connected to one another.

Both systems are made up of one upper thermostat and one element.

They both connect to the breaker from L1 and L3 wires – so that’s two wires attaching to both of the upper thermostats.

Now for both of the upper thermostats, L4 and T2 will connect it to its element.

Each upper thermostat will have four wires connected to it. Each element will have two wires connected to it.

Simultaneous Thermostats When Both Operate Separately

Thermostats and elements work independently from one another, allowing for a quicker heating of the water for the first hour.

This system also allows for better recovery time, improving the health of the overall circuit and system.

Separately wiring your thermostats will mean that the wattage is increased due to the doubling up of systems.

For example:

  • Using 4500W elements will mean that you have 9000W in total. You’ll need a 50A breaker and gauge 6 wire. Alternatively you can use two 30A breakers and two gauge 10 wires.
  • Using 5500W elements means that your total wattage would be 11,000W. This will require a 60A breaker and gauge 6 wire. Another option is two 30A breakers with two gauge 10 wires.

Using a larger breaker and gauge of wire allows the wire to remain cooler and therefore stay more efficient throughout usage.

When this system is off peak, you should connect the lower thermostat to a timer so that you can save energy during these times. Newer models are coming with these features to make them more appealing to the customer.

How To Wire These Thermostats

Wiring these thermostats is exactly the same for both of them as they are both being used in the same way, but they aren’t connected to one another.

Use two wires (wire 1: red, wire 2: black) – both connected to the breaker with a 6 gauge wire.

The red wire will connect to the upper thermostat through L3 as well as the second upper thermostat.

The black wire will connect to the first upper thermostat through L1 as well as the second upper thermostat in the same position.

The first upper thermostat will connect to the element through two wires – blue and yellow. The second upper thermostat will connect to the second element in the exact same way.

Alternatively, you can use 2 ECO protected thermostats with two 30A breakers and 10 gauge wire instead of what we have detailed above.

Can You Set Two Different Temperatures Through Simultaneous Wiring?

Yes, you can set the temperature while using simultaneous wiring if you want to.

You can change the water temperature within the heater using the Tork TU, Intermatic GM40-A, or Tork DTU with a 24-hour timer with your simultaneous wiring setup.

How To Wire Water Heater Thermostats

You will need to choose which part of your system has the power – either the upper thermostat and upper element, or the lower thermostat and lower element.

However, both of these sections cannot have power at the same time.

To set two different temperatures at the same time, you will need to wire the thermostats so that the upper part is seperate from the lower section.

Now use a GM40 timer to set the power to whichever part of the circuit that you want to have it.

Now, as the system is running, you will notice that there is only power going to the section that you designated power to.

Let’s say that you set the lower portion of the circuit to have the power.

This means that the lower thermostat and element will be working as normal to heat the water.

However, the upper thermostat and element will have zero power going to it and therefore will not be heating the water.

This is called redundant water heating as nothing is happening.

Some use this to heat the water in the tank quicker when cold water first enters the tank.

Once your timer activates, the power to the lower section of the water heater will turn off.

Now the power will head to the upper portion of the circuit and start heating that water. The upper thermostat should be set to a higher temperature.

As the water will have reached the lower temperature of the low temperature setting, it will start heating to the upper’s higher temperature setting.

The system will not turn off until the water has reached the upper portion’s temperature setting.

Bear in mind that the lower portion of the tank will cool quickly as new water comes into it, so this method is only effective at making very hot tanks of water for a short period of time.

How To Complete This Wiring

Setup your GM40 timer so that it is connected to the 240V breaker into L1 and L2 on the timer.

NC on the timer will connect to the second upper thermostat, and NO will be connected to the first upper thermostat.

NC2 will also connect to the second upper thermostat, and NO2 will connect to the first upper thermostat.

Both of the upper thermostats will also be connected to their elements with two wires.

What’s The Point Of Doing This?

Some people will not understand the importance of doing this, and they might never find a need for it.

That’s fine, but it’s useful to know that there is an option to set your thermostats to two different temperatures through simultaneous wiring.

For example, if you have a very hot load of laundry to do, you might only be able to reach such a high temperature by setting the tank to two different temperatures.

Making Your Own Thermostat

You might be wondering what we mean by this – how can you make your own thermostat? We are talking about using an upper thermostat to make a lower thermostat!

Some people find that this is a better method of replacing their current thermostat if the water heater has foam insulation.

This is due to the fact that replacing a lower thermostat with an ECO protected newer element will be unnecessarily difficult if there is foam insulation in the way.

To make a lower thermostat from an upper thermostat, you will need to remove the screw from the middle of the upper thermostat which is holding the two sections together.

Now separate the top from the bottom section.

You can now use this lower section as a lower thermostat! You can use this for a two water heater model that we discussed earlier.

Bear in mind that this is not always suitable for the setup that you might have.

For example, a simultaneous or single-tank water heater setup might require the ECO to operate correctly.

The ECO protects your system from overheating and is sometimes required for safe use of water heaters.

Furthermore, you should not remove the ECO protection from the upper part of your water tank.

Only make your own thermostat if you are confident that it is suitable for your needs. Otherwise you might find that purchasing a new thermostat is the way to go.

More On Redundant Thermostats

A redundant thermostat, as we mentioned earlier, is a system in which only the lower element operates and heats the water. The upper element is disconnected and therefore no power reaches it.

This allows the water tank to respond immediately to the new cold water entering the tank, allowing it to heat up more quickly and efficiently.

Both of the thermostats will control the lower element.

As the lower element heats the bottom of the tank, the hot water will rise and push the colder water to the bottom.

This is how the tank heats altogether so that there are no cold spots.


We hope that this guide was helpful for those who were looking for information on how to wire a water heater.

Wiring your water heater is no easy feat, but it can be done. Just make sure that you know how you want to wire the heater before you start disconnecting things.

If you feel uncertain about your ability to wire your own water heater, don’t hesitate to reach out to a professional and get some advice.

You might even prefer for them to do the wiring over you.

Good luck!

author avatar
Anthony Barnes
Anthony Barnes is the founder of Water Heater Hub and a second-generation plumber by profession. Before developing Water Heater Hub, Anthony Barnes was a full-time plumber, and he has undertaken a wide variety of projects over the decades. As a second-generation plumber, it was easy for Anthony to get used to the technicalities of all from a tender age


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