What size wire is needed for a 40 gallon electric water heater?

What size wire is needed for a 40 gallon electric water heater?

electric water heater

The best size wire for a 40 gallon electric water heater is a 12 AWG wire.

A 40 gallon electric water heater is a typical size for a standard household or small business. These heaters have an energy output capacity of between 16,500 and 30,000 BTU per hour, with the average at about 22,500 BTUs which means that they use around 5240 watts on average. This results in needing a 15 amp circuit from the breaker box to power it safely and efficiently.

Here is a very popular 12 AWG wire on amazon.

Understand Your Water Heater First

When consumers purchase a water heater, they rarely check to see if it matches the size of their home and particular needs. Although there is a common misconception that water heaters usually last up to 15 years, this is not always true as they can break as early as five years after purchase. It is important to understand the type of water heater you have, its energy output, and how much your home will use on average per year before buying a replacement or additional unit. Energy efficiency becomes an important factor in choosing a new furnace as well as other factors such as space requirements for installation and any special instructions supplied by the manufacturer.

Here are some thing you should consider before purchasing a new water heater:
  • Wattage - The wattage of the water heater is an important factor to consider. More wattage means the water heater will heat much quicker. While this is a benefit, it also uses more energy and can be a deterrent when you are trying to reduce your electric bill.
  • Water Heater Size - This is a more complicated issue that involves a number of factors including how many people in your household use hot water. Many different formulas have been created to determine the size of tank needed for an average family's usage per day [remember, some people don't take showers every day]. The most simplest way to determine capacity from any home improvement store employee or manufacturer representative.
  • Wire Size Needed - The wire size you will need is based on your total length of wire needed. The 40 gallons electric water heater has a capacity of 10,000W so if you are using an outside faucet or other device that draws more than 18 amps, then multiple wires will be necessary to prevent overloading the main circuit breaker.

What happens if you use the wrong wire size?

If you use the wrong wire size you will either overheat the wire or under heat the wire, both of which can cause fires. Overheating can cause a fire because it causes the insulation on the wires to deteriorate faster than usual which in turn makes them more likely to short circuit and spark against other objects. Under heating, on the other hand, is an equally bad problem that occurs when there isn't enough room for heat to escape from inside the wire casing. If there isn't anywhere for this heat to go then it builds up until it starts melting things around it, including itself.

What size wire should you use?

The best size wire for a 40 gallon electric water heater is a 12 AWG wire because its energy output capacity nearly matches with what's needed to run a 40 gallon electric water heater. Another good choice would be 16 AWG wire which has the same output capacity as 12AWG wire, but is more compact in size and this allows for better heat exchange with less risk of overheating.

What Size Breaker for 40 Gallon Water Heater?

20 amp breaker

A 40 gallon water heater will be quite fine with a 20 amp breaker. The 20 amp breaker will be enough to power the heating element, but you might have to switch off your heater when it's not in use so that both of them do not heat up at the same time.

Choosing the right size breaker for your water heater is crucial in ensuring safety and efficient operation of the latter. The amp difference is a significant factor in determining which circuit's breaker you should use. A small amount of ampere difference may trigger an electrical fire, so be extra careful when choosing the right breaker for your water heater.


Bottom Line: A 16 AWG or a 12 AWG wire will do fine for your 40 gallon electric water heater. It's very important to make sure you use the right size when wiring any appliance because it not only ensures that its performance matches what it requires, but also prevents hazards from fire and electrocution.

15 Amps

All you need to know about using 15 amps. Click to find out.


About Author:

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Hi, I'm Kevin Pommells, a lover of camping and the great outdoors as everyone says nowadays. I'm also a passionate soccer fan and the proud owner of CamperRules.com, a website dedicated to helping campers and outdoor enthusiasts make the most of their adventures. With years of experience exploring the wilderness and a deep love for the sport of soccer, I'm always looking for new ways to combine my two passions and share my knowledge with others. Follow me for tips, tricks, and insights on all things camping and outdoor recreation.

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