What Size Wire for Electric Hot Water Heater? (w/Size Chart)

What size wire for the electric hot water heater to use is one of the most crucial questions for first-time buyers of such appliances. Although most products require a 12 gauge AWG for 20 amps, some different brands may have specific recommendations.

Moreover, several factors can influence electric water heater wire size. This article explores these parameters to help you decide the most appropriate cable size for your water heater’s wiring requirements.

What is the Correct Wire Size for My Electric Water Heater?

Determining what gauge wire for the electric water heater to pick can be confusing, especially to homeowners with limited electrical knowledge or first-time owners.

The best method to determine a water heater’s electrical requirements is to read the owner’s manual. Here, you can find the exact wire size and other technical specifications for a particular water heater brand, model, and series. Some might even have a diagram showing how to wire a electric water heater.

For example, Rheem offers the following wire size chart for its electric water heaters.

Hence, you might want to check your electric water heater user’s manual to know the correct wire size, including whether to use a 10/2 or 10/3 wire.

Unfortunately, some brands might not offer this information. So, we will look at some of the most common ways to determine the best possible wire size for your electric water heater based on various parameters.

1. Wire Sizes according to Electric Water Heater Type

Electric water heaters come in two types: storage-tank and tankless. Although tankless units are 8% to 34% more energy efficient than storage-tank versions, they have a higher wattage rating.

For example, electric tankless water heaters can use up to 30 kilowatts to function. Meanwhile, the average tank-type water heater only consumes about 1,125 watts or 1.125 kilowatts.

As more electricity means a thicker wire is required, you can expect the ones used for electric tankless water heater units to have a larger diameter than a conventional electric one. Strange as it may sound, a bigger diameter translates to a smaller AWG number.

To have a clearer understanding, you can have a look at the table below:

As for storage-tank electric water heaters, we will discuss them in the following sections.

2. Wire Sizes according to Electric Water Heater Capacity

Storage-tank electric water heaters follow the same rule as tankless units. The higher the appliance’s wattage rating, the smaller the AWG number or the wider the cable’s diameter.

In this case, the larger the water heater capacity, the more wattage it will require. So a 30 and 50-gallon water heater wire size should be 14 AWG. However, a 20-gallon unit will only require a 16 AWG gauge, meaning its wire diameter needs to be smaller.

Here is a summary of wire sizes for the most common storage-tank electric water heaters. Notice that 14 AWG can work for 40-gallon electric water heater units as it does with 30- to 80-gallon versions.

3. Wire Size according to Water Heater Amperage Rating

Some homeowners consider their water heater’s amperage rating to decide on the correct wire size. Amperes and volts are wattage factors, allowing homeowners to determine the water heater’s watts.

For example, a 240-volt electric water heater with 5000 watts draws 20.83 amps. These appliances have a continuous load, requiring a 125% amperage adjustment. Hence, our example draws 26.04 amps (20.83 amps x 125%).

The table below suggests that our example (26.04 amps) needs a 10 AWG wire. Interestingly, most homeowners use a 10/2 wire for hot water heater units, meaning two 10 AWG wires. One cable is a “hot wire,” while the other is a neutral one.

4. Wire Size according to Water Heater Wattage Rating

Most electric water heaters do not print their amperage ratings on product labels. Instead, they list the electric water heater’s wattage rating.

We already know that the higher the water heater’s wattage rating, the bigger the electric cable diameter we need (i.e., the smaller the gauge or AWG number).

For instance, a 14 AWG wire is sufficient for electric water heaters with a wattage rating not exceeding 2 kilowatts. If a 1600-watt unit runs on 120 volts, a 16 AWG wire will be enough. Meanwhile, 100-gallon, 10-kilowatt, 240-volt units require 8 AWG wires.

The following table describes the wattage-based wire requirements considering a 120-volt water heater.

5. Wire Size according to Types of Wires for Water Heaters

Electric water heaters require one of two electrical cables to convey power to the unit. These are non-metallic (NM) and metal-clad (MC) cables.

Non-metallic electrical cables (also known as “Romex”) are the most common wiring in many homes. It has a flexible, non-metallic sheathing. Hence, the name. These cables have at least two conductors: one “hot” and one “neutral.” They can handle a maximum of 600 volts.

The wire sizing for NM cables is as follows.

As for metal-clad cables, their sheathing is aluminum, making them impermeable to shearing and piercing forces. Their amperage suitability is as follows.

Frequently Asked Questions

The importance of choosing the right wire size for electric hot water heater

Choosing the right wire size for 220V hot water heater units is crucial to prevent electrical mishaps.

It is worth remembering that electrical cables are “highways” for electrical energy to pass from the source to the appliance. Hence, electricity must “travel” effortlessly without any resistance.

Too small, and the wire cannot accommodate electrical flow, leading to overheating, short-circuiting, and cable insulation degradation. It can become a fire hazard because of high resistance-related heat generation.

Meanwhile, larger-than-necessary wires are impractical (a waste of money).

What size breaker for an electric hot water heater?

Most electric water heaters require a double-pole, 30-amp size breaker. Of course, everything depends on the appliance’s electrical ratings. As a rule, the circuit breaker should accommodate the water heater’s load.

For example, a 4500-watt water heater draws about 18.75 amps (4500 watts ÷ 240 volts = 18.75 amps). However, water heaters are continuous-load appliances, requiring amperage adjustment by 125%, which brings us to 23.44 amps.

Hence, a 25- or 30-amp breaker is sufficient for a 4500-watt water heater.

Conclusion

We cannot provide a definitive answer as to what size wire for electric hot water heater you should use. Although the most common wire size is 12 AWG, everything still depends on your electric water heater and its electrical specifications.

As a rule, you should always pick a wire with a lower AWG number the higher the electric water heater’s wattage, amperage, and capacity.

Other tips & tricks you can refer to:

• Steps for Adjusting the Temperature on an Electric Water Heater
• 5 Simple Steps to Turn On Electric Hot Water Heater