How To Tell If Water Heater Is 120 Or 240

Posted by: Mas Broto
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How To Tell If Water Heater Is 120 Or 240

There are two easy ways how to tell if a water heater is 120 or 240. Please keep in mind that these methods are based on general rules and work for most residential units. Some homes are set up differently, so these rules to tell if a water heater is 120 or 240 may not work.

When looking for a water heater, one of the most important things you should do is make sure it has the right voltage for your installation. Most tank or conventional water heaters switch from 120 volts to 240 volts when they reach about 20 gallons. But there are exceptions on both sides of that line.

How can I figure out the voltage of my water heater?

The quick and easy way to know the voltage of your water heater is to check the data tag.

In general, a 240-volt breaker will place on the left, and a 120-volt breaker will place on the right. If you can’t tell from looking at the breaker what the water heater voltage is, you’ll have to figure it out another way. You need to check the power going to the water heater with a multimeter or voltmeter.

Finding out the voltage of the water heater with this method is risky. You need to be very careful because you’ll have to test live wires. It’s dangerous, and it’s easy to do it wrong.

How to check if your water heater has 120 or 240 volts with the multimeter

Turn off the electricity to the water heater. Take off the upper access panel, the safety cover made of plastic, and the insulation. The thermostat gets power just above the button that resets it. This picture shows that they have the numbers 1 and 3.

When the power is on, each wire has 120 volts. Set your meter at 120 volts or above, then put one probe on one of the terminals and the other on the water heater tank. Scratch the tank with the other probe to get good ground, and then check your meter for a reading. There should be no voltage.

Set your multimeter to 240 volts AC or higher. With the multimeter probes, touch each terminal, #1 and #3. The screen should show 240 volts. Even if your meter says there is no power, one of the terminals could still have 120 volts, so don’t touch anything.

Check each terminal again the same way you did before, but this time with the power on. There should be 120 volts at each terminal. If you have lost power on either side, the problem could be the breaker or where the wiring connects to the water heater, which is usually at the top of the tank.

What’s the difference between a 120 and 240 water heater?

A heater with 240 volts may work better than one with 120 volts. Voltage is a measure of how much power a source of electricity has to do a certain job, in this case, electric water water. Since they don’t use as many amps, it’s no surprise that 240-volt water heaters are really common in most homes.

A 120-volt heater will always use a circuit breaker with one pole, while a 240-volt heater will always use a circuit breaker with two poles. Most 240-volt water heaters are bigger. In fact, 240-volt heaters are used in most homes today. But don’t just assume this is true for your home. It’s always best to check if a water heater is 120 or 240 and be safe.


You must know for sure that you are getting the right voltage. If you connect a 120-volt water heater to a 240-volt circuit, the heater will not work. It will give off four times as much heat as it was meant to.

On the other hand, if you connect a 240-volt water heater to a 120-volt circuit, the heater won’t work most of the time. If it does work, the amount of heat it gives off will be much less than what you need to heat the room.

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Mas Broto

Have been in the heating and air conditioning (HVAC) industry for over 20 years. He is person that will grow and thrive to learn more about the HVAC industry throughout his career. Mas Broto is also a blogger, who's dedicated to bringing you the best knowledge to get ahead in the game of life.

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