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

Fact checked by Stephen Conklin

what size wire for electric hot water heater

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.

Table of Contents

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:

Tankless Electric Water Heater (Watts) Diameter in Inches Diameter in Millimeter Wire Size
7600 watts 0.2043 5.18922 4 AWG
9600 watts 0.2294 5.82676 3 AWG
11500 watts 0.2576 6.54304 2 AWG
13400 watts 0.2893 7.34822 1 AWG

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.

Electric Water Heater Size Wire Size
10 to 20 gallons 16 AWG, 18 AWG, 20 AWG
30 to 80 gallons 14 AWG
90 gallons 8 AWG, 10 AWG, 12 AWG, 14 AWG
100 gallons 6 AWG, 8 AWG, 10 AWG, 12 AWG, 14 AWG

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.

Amperes Voltage Wire Size Diameter in Inches Diameter In Millimeter
<20 240 12 AWG 0.0808 2.05232
20 to 30 240 10 AWG 0.1019 2.58826
30 to 40 240 8 AWG 0.1285 3.2639
>50 240 6 AWG 0.162 4.1148

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.

Water Heater Wattage Rating Diameter in Inches Diameter In Millimeter Wire Size Based on a 120-volt System
2000 watts 0.1019 2.58826 10 AWG
2500 watts 0.1285 3.2639 8 AWG
3000 to 3500 watts 0.162 4.1148 6 AWG
3800 to 4500 watts 0.2043 5.18922 4 AWG
4800 watts 0.2294 5.82676 3 AWG

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.

Wire Size Amperage Suitability
14 AWG 15 amps
12 AWG 20 amps
10 AWG 30 amps
8 AWG 40 amps
6 AWG 55 amps

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

Wire Size Amperage Suitability at 75OC
14 AWG 15 amps
12 AWG 20 amps
10 AWG 30 amps
8 AWG 50 amps
6 AWG 65 amps
4 AWG 85 amps
2 AWG 115 amps

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.


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:

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