Water Heater Wire Size Chart: Which AWG Gauge Wire?

Big enough wire won’t fry the water heater circuit. What size wire do you need for a hot water heater? The choices range from 8 AWG, 10 AWG, 12 AWG, 14 AWG, 16 AWG, and even 18 AWG wire. We will explain this in simple terms the same as we did with the water heater breaker size here (there are some similarities).

what happens if you use too small a wire for a water heater
Using a too small wire for a hot water heater (20 AWG copper wire, for example) can result in the wire catching fire due to the very high temperature in the wire (connected to electric resistance).

Namely, water heaters predominantly use a 4500 watt 240V electric heater. In order to figure out the size of the wire gauge we need, we have to match these two things:

  1. Water heater amp draw. This is the electric current that the wire has to be able to carry. Thicker wires (lower AWG number) carry more amps. If you choose a wire that is too small (like 20 AWG), you risk frying the entire circuit. As we have pointed out in the water heater amp chart here, most electric hot water heaters run on a maximum of 18.8 amps.
  2. Wire size or AWG wire ampacity. Example: A copper 14 AWG wire has a median ampacity at 75°C (167°K) of 20A. That means that it can safely carry an electric current of up to 20 amps.

To determine the water heater wire size needed, you have to first figure out the amps your electric heater draws (it’s usually 18.8A) and then match those amps with an adequate wire thickness. We have already done all this for you and summarized the calculations in the water heater wire size chart below.

what size wire for 20 gallon 30 gallon 50 gallon hot water heater
Examples of what size wires you will need for most 20-gallon, 30-gallon, and 50-gallon hot water heaters.

To illustrate how to size a water heater wire, let’s look at this simple example:

Let’s say you have a 50-gallon water heater. All 50-gallon water heaters use 4500 watt 240V heaters that draw 18.8 amps of electric current. What size wire do you need for this 50-gallon water heater?

You just have to consult the AWG wire ampacity chart here. This is a screenshot in the vicinity of 18.8A currents:

what awg wire size for a hot water heater
On the left, you have wire sizes (10 AWG, 12 AWG, 14 AWG, 16 AWG, 18 AWG). On the right, you have the corresponding ampacities (35A, 25A, 20A, 17A, 14A).

As you can see, the 18 AWG and 16 AWG wires cannot handle 18.8 amps. That means that if you install this hot water heater with 16 AWG wire, the wire will likely fry.

The wire closest and over 18.8A is the 14 AWG wire. That’s the right choice for 30-gallon, 40-gallon, 50-gallon, 60-gallon, 70-gallon, and 80-gallon electric water heaters as you will see in the all-encompassing chart below.

You could also go with thicker 12 AWG or 10 AWG wires but that’s overkill. However, if you have a 90-gallon or 100-gallon water heater (these have higher wattage heater than 4500W and can draw over 50 amps), you may need a wire as thick as 6 AWG.

Based on the commonly used water heater wattages we explained here, these are the right wire sizes to choose for different water heaters:

Water Heater Wire Size Chart

Water Heater Size: Wire Size:
10 Gallon Water Heater 16 AWG (also 18 AWG or 20 AWG)
20 Gallon Water Heater 16 AWG (also 18 AWG or 20 AWG)
30 Gallon Water Heater 14 AWG Gauge Wire
40 Gallon Water Heater 14 AWG Gauge Wire
50 Gallon Water Heater 14 AWG Gauge Wire
60 Gallon Water Heater 14 AWG Gauge Wire
70 Gallon Water Heater 14 AWG Gauge Wire
80 Gallon Water Heater 14 AWG Gauge Wire
90 Gallon Water Heater 14 AWG, 12 AWG, 10 AWG, 8 AWG
100 Gallon Water Heater 14 AWG, 12 AWG, 10 AWG, 8 AWG, 6 AWG

Essentially, you can see that most water heaters use 4500 watt heater and require 14 AWG copper gauge wire. This is a wire that can handle up to 20A and the heater only draws a maximum of 18.8A.

Smaller 10-gallon and 20-gallon heaters use below 2000W heaters. 1600 watt 120V heater that draws 13.3 amps is the most commonly used for small water heaters. For these heaters, you don’t actually need 14 AWG; you can go with 16 AWG wire size because it can handle 14 amps. If you are in doubt, just use the 16 AWG; it might be overkill, but it is the safest bet.

Bigger 90-gallon and 100-gallon water heaters use more powerful heaters. Some can still use standard 4500 watt heaters but it is not uncommon to see a 100-gallon water heater powered by a 10,000 watt water heater (240V circuit). This heater draws 41.7 amps; consulting the AWG wire capacity chart, you will see that you need an 8 AWG wire size (with 50A ampacity).


Here is the bottom line on water heater wire sizing:

Always check the amp draw of the water heater and match it to the wire ampacity. Wire ampacity has to be higher than the amp draw. If the wire is too small to carry all the electric current needed to power the water heater, it will go up in flames.

If you need any help with what size wire do you need for your hot water heater, you can use the comments below and we will try to help you out.

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