How Many Amps Does a Water Heater Use?
Having the right amperage for your water heater prevents your home's electrical system from becoming overwhelmed
Highlights
Most modern electric water heaters utilize 18.8 amps with 240 volts and 4,500-watt heating elements.
If you have a gas water heater, expect it to use 12 amps with 115 volts.
The average 40-gallon tank requires a 30-amp breaker.
While tankless water heaters generally use more energy compared to traditional heaters, the lifetime usage is lower because tankless heaters only run when water is being used.
With a tankless water heater's capacity determined by gallons used per minute, models with higher flow rates tend to use more electricity.
With so many different types of water heaters on the market, it’s hard to know how many amps your water heater needs. Without the right amperage, your home’s electrical system can quickly become overloaded. Water that takes a long time to heat or breakers that tend to trip without warning could be signs that you need to bump up your electrical system’s capabilities to handle your water heater.
If you’re thinking about an upgrade, there are a few factors that determine how many amps your new water heater will need.
What is the Standard Amperage for an Electric Water Heater?
Most electric water heaters use 18.8 amps with 240 volts and a 4,500 watt heating element. A gas water heater uses fewer amps—about 12 Amps with 115 volts. The average residential container heater has a 40-gallon tank and usually requires a 30-amp breaker.
The exact amount of amperage used varies between water heaters and depends on key elements like the type of water heater it is, the fuel type it requires, and its capacity.
NEC 80% Rule
When determining breaker size for a new hot water heater, it's important to follow the amperage rules set by the National Electrical Code (NEC). The NEC's 80% rule states that a breaker can only be loaded up to 80% of its full amperage. The NEC requires circuit breakers to be sized at 125% of the intended load.
Water Heater Types: Tank vs Tankless
Water heaters can be one of two types: tank or tankless. Traditional tank water heaters, sometimes called storage or container heaters, have tanks that physically hold water and heat it constantly. Tankless water heaters have coils that heat the water on demand while you’re using it.
While tankless water heaters generally use more energy and require more amps than their tank counterparts, they require less power over their lifetime because they only run when water is needed.
You’ll need a 30-amp breaker for an average 40-gallon tank water heater. This breaker size is very common, so it’s likely that you won’t need to upgrade your electrical system to handle the necessary amount of power when installing a tank this size.
A tankless water heater requires 120 amps to run on average. If your home is older, you’ll likely need a professional electrician to upgrade your system and increase the amount of amperage available in your home.
Fuel Type: Electric vs Gas Water Heaters
An electric water heater (with a tank) needs a 240-volt circuit with a 30-amp breaker. A tankless electric water heater needs a 120-amp breaker.
A gas water heater with a tank requires 30 amps, while a tankless gas water heater requires a 120-amp breaker.
Water heaters run on either electricity or natural gas. Electric water heaters generally cost less than gas ones, but it costs more to keep electric units running. Tank or tankless, you will likely need to upgrade your electrical system to accommodate a new electric water heater.
Gas water heaters are physically attached to a gas line, which means they are often more expensive to install initially. But on the plus side, you usually won’t need to upgrade your electrical system to accommodate a gas water heater unless you live in a very old home with fewer power capabilities.
Other Factors That Influence Water Heater Amperage
Water Heater Capacity
The total amount of electricity your water heater uses depends on its capacity, as the tank size can vary. Larger tanks will require more electricity in order to heat all of its water.
A 50- to 60-gallon storage tank is enough for a single person or a small family (three people at most), while a medium 80-gallon tank will accommodate three to four people. In general, you should increase your tank size by 10 gallons for each extra person in your home.
The capacity of your tankless water heater is determined by the gallons per minute, or the flow rate, that it can supply. The higher the flow rate, the more electricity your system will require.
If you want to run the dishwasher, do a load of laundry, and take a hot shower at the same time, you will likely need to upgrade your electrical system to serve your needs.
Energy Efficiency
Some units are more energy-efficient than others. In general, electric water heaters have higher energy efficiency ratings than gas water heaters. Tankless water heaters are typically more energy efficient than tank-type water heaters.
Also, energy-efficient units that do not run constantly, or newer models, will require fewer amps. If your water heater is over a decade old, it’s likely not as energy efficient as its newer counterparts. Consider upgrading to a new one to reduce its electricity needs, or you will eventually need to upgrade your electrical system to accommodate it.
Frequently Asked Questions
Yes, this would be an appropriate choice. In order to comply with the NEC's rules, you'll need to install a circuit breaker that's 125% larger than the intended load. In this case, you'll multiply 30 amps by 1.25 to find the necessary breaker size. Plugging that equation in for your 30-amp water heater will leave you with a 37.6-amp breaker. If your current water heater keeps tripping the breaker, it might be time to talk to a plumber or electrician about upgrading your water heater's setup.
If you're ready to get a quote for water heater replacement cost, a local plumber will be able to assess your home's needs. A plumber will look at the size of your household, your existing plumbing, your existing breaker, and other factors to ensure that you can select the most efficient water heater possible.