Having the right amperage for your water heater prevents your home's electrical system from becoming overwhelmed
Most modern electric water heaters use 18.8 amps with 240 volts, while your gas model uses 115 volts for controls.
Your average 40-gallon tank needs a 30-amp breaker, and an electric tankless water heater needs a 120-amp breaker.
You can estimate your water heater amps by checking your tank size, heating element wattage, temperature setting, and hot water usage.
Hiring a local electrical professional provides reliable support with breaker sizing and electrical panel upgrades, keeping your water heater installation safe and code-compliant.
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.
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.
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 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.
| Tank Water Heater Size | Size of Circuit Breaker |
|---|---|
| 20 gallons | 20—30 amps |
| 30 gallons | 30 amps |
| 40 gallons | 30 amps |
| 50 gallons | 30 amps |
| 75 gallons | 30 amps |
| 90 gallons | 30—40 amps |
| 100 gallons | 30—40 amps |
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.
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.
When calculating water heater replacement costs, you should add the cost of potential electrical panel upgrades. Items that will affect your water heater amperage include the amount of water the tank will hold, the temperature setting you’ll use, and the frequency with which you’ll use hot water. A local water heater installation professional can give you advice based on the way you’ll use the appliance.
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 the 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.
The type of heating element inside the water heater and the wattage it requires affect the size of the circuit breaker you’ll need.
Standard: A standard, or low-density, heating element requires less watts for operation, meaning you might be able to use a 20-amp breaker, although a 30-amp breaker is more common. It heats the water slowly by using less electricity.
High-efficiency: A high-efficiency, or high-density, heating element requires more watts for operation to heat the water faster. Although a 30-amp breaker is common for these water heaters, some models might need a 40-amp breaker.
When you run the water heater at a higher temperature than average you might need more amps in your circuit breaker, although this isn’t always the case. The average water heater temperature setting ranges from 120 to 140 degrees Fahrenheit.
When you set the temperature at 140 degrees or higher, the water heater will use more energy to maintain the higher temperature. If you’re running a large-capacity water heater that uses more watts at the same time you turn up the temp, a 40-amp breaker might be a smart choice to avoid potential problems. However, if a higher temperature setting is the only above-average aspect of your water heater, it rarely requires more than a 30-amp breaker.
If you have a larger-than-average electric water tank and if your family uses hot water constantly, you might need a 40-amp breaker. When the size and wattage of your water heater tank are close to surpassing the limits of a 30-amp breaker, frequently using hot water could push it over the edge. Your installation professional may then suggest going with a 40-amp breaker.
However, if you use an average 40-gallon or smaller tank, you’ll rarely need a 40-amp breaker, even if your family uses hot water constantly.
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.
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