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How Many Amps Does A Tankless Water Heater Use?

5 Star Plumbing > Blog > How Many Amps Does A Tankless Water Heater Use?

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The water heater is among the most crucial but underappreciated pieces of equipment in your house. If you’re planning on getting a new one, be sure to factor in the amperage it will use.

The number of watts determines an electric water heater’s wattage that you’ll use per day, not by its amperage. The amperage is vital to ensure that your current electrical system isn’t overloaded. The typical voltage for an electric water heater is 240V, while the specific power consumption is 4500 Watts. A gas water heater usually consumes less than 12 Amps at 115V (in the US and Canada).

  1. Heater Type
  2. Fuel Type
  3. Capacity
  4. Energy Efficiency

Understanding the number of amps required by a water heater is critical information for any homeowner. However, choosing a water heater may be difficult, given the plethora of available alternatives.

With so many different types of water heaters on the market, determining how many amps your current water heater requires might be difficult. Your home’s electrical system can quickly become overloaded if you don’t have the correct amperage. 

Signs that your electrical system isn’t big enough to handle your water heater include having to wait long for the water to heat up or breakers that trip without notice. When thinking about getting a more powerful water heater, a few things to consider when calculating how many amps your new unit will need are

If you’re looking for Sacramento tankless water heater repair or installation services, you’ve come to the right place. 5-star plumbing’s professional plumbers can assist you with any of your tankless water heater needs.


What is the Standard Amperage for a Tankless Water Heater?

On average, an on-demand heater requires 120 amps to run. That is significantly higher than the traditional units that only need 30 amps to power them.

If you live in an older home, the amperage available is only 100-200. That will require a professional electrician upgrade to your electrical system, which may include adding a subpanel of circuit breakers to increase the total amps available. The key elements that affect the amount of amperage used by water heaters include the type and fuel requirements of the heater and its capacity.


Power Requirements For Tankless Water Heater

Tankless water heaters, whether the gas or electric type, are very energy-efficient when compared to traditional water heaters. While a gas tankless device utilizes propane, other sections of the water heating system still rely on electricity. So, what electrical specifications does a tankless gas water heater have?

Tankless gas water heaters typically require a 15- or 20-ampere 120-volt circuit to operate the electric pilot light and control panel. According to the National Electrical Code, these types of water heaters shouldn’t have courses that exceed 120 amperes and should be protected at 150 amperes max.

Depending on where you live, your tankless gas water heater will require different amounts of electricity. That is because while some areas have access to 220 volts worth of power supply, others only have 110 volts. Therefore, the unit’s wattage determines how much voltage the circuit requires. Usually, this ranges from 208V up to 277V.


Сan My Panel Handle a Tankless Water Heater?

Do not utilize the same calculated amperage as your final tankless water heater size breaker. You’ll be putting yourself and others in danger if you do since there will be no protection in case of a power surge. In addition, according to the National Electric Code (NEC), a circuit breaker should only handle 80% of its total capacity.

So, an 80-amp breaker should be used for a 100-amp tankless water heater. If not, get a circuit with a higher amperage to avoid any problems. If you have a tankless water heater, you must use the appropriately sized circuit breaker. You could be in danger of electrical fires if you don’t. According to NEC requirements, a circuit breaker should only be able to handle up to 80% of its maximum capacity.


Is 200 AMP Service Enough For a Tankless Water Heater?

That is a tricky question to answer without additional information regarding your setup. Some tankless water heaters require as little as 20 amps, while others need up to 200 amps. It all depends on the unit’s size and power and your home’s electricity consumption. Contact a professional if you’re unsure how much energy your tankless water heater requires. In general, most tankless water heaters should be able to run on 200 amps of electricity.


How to Calculate How Many AMPS a Tankless Water Heater Consumes

Electric tankless heaters use electricity to generate heat for water. Because the task of heating water is quite resource-demanding, these types of tankless water heaters require a strong flow of electric current or amps. So, how many amps do tankless water heaters typically use?

We can identify precisely how many amps a tankless water heater uses because we know two crucial elements:

Overall power or wattage. The most powerful water heaters are usually electric. For example, the power input for an electric tankless water heater ranges from 10,000W (10 kW) to 40,000W (40 kW).

Voltage. All electric tankless water heaters require a 240-volt circuit to operate efficiently.

By utilizing the electric power equation (P = I×V), we may calculate the current as follows: 

P = I x V.

I (amps) = P (watts) / V (volts)

Example: We can determine how many amps a 30 kW tankless water heater uses on a 240-volt circuit by using the electrical power equation: I (amps) = 30,000W / 240V = 125 amps

A 75,000 BTU heater draws 125 amps. For installation, you’ll need many 20-amp and 30-amp breakers. We’ve calculated amp consumptions for tankless water heaters ranging from 10 to 40 kW and listed them in the table below:

Tankless Heater Size (in kW)Electrical Current (in Amps)
10 kW42 amps
11 kW46 amps
12 kW50 amps
13 kW54 amps
14 kW58 amps
15 kW63 amps
16 kW67 amps
17 kW71 amps
18 kW75 amps
19 kW79 amps
20 kW83 amps
21 kW88 amps
22 kW92 amps
23 kW96 amps
24 kW100 amps
25 kW104 amps
26 kW108 amps
27 kW113 amps
28 kW117 amps
29 kW121 amps
30 kW125 amps
31 kW129 amps
32 kW133 amps
33 kW138 amps
34 kW142 amps
35 kW146 amps
36 kW150 amps
37 kW154 amps
38 kW158 amps
39 kW163 amps
40 kW167 amps

Gas vs Electric

Based on both experience and knowledge, we can confirm that a gas tankless water heater usually does not need an upgraded home electric system, whereas electric tankless heaters do. Additionally, it’s essential to know that most of the gas tankless water heaters we’ve reviewed on this blog are energy star certified; some even qualify for federal tax rebates.

Nevertheless, traditional heaters do not require an energy star label to help evaluate a unit’s efficiency.


How Many AMPS Does a Gas Tankless Water Heater Use?

All tankless gas water heaters need a 15-ampere or 20-ampere 120-volt circuit to power the electric pilot light and control board. Instantaneous water heaters must have circuits of no more than 120 amperes and be protected against overloading of no more than 150 amperes, according to the National Electrical Code.


 How Many AMPS Do Electric Tankless Water Heaters Require?

A typical tankless water heater consumes 120 amps when operating. If you have an older home, you’ll almost certainly need the help of a professional electrician to upgrade your infrastructure and increase the amperage available on your property.

Tankless water heaters are more energy-efficient ways to heat water on demand, and they can help you save money on your power bill in the long term. In comparison, a traditional tank water heater takes less electricity to run. Before making a purchase, get advice from a professional electrician to ensure your property can support a tankless water heater.


Should You Change Your Heater’s Fuel Type?

Although you might think it’s impossible to change your water heater from electric to gas (or vice versa), this may not be the case. If you’re interested in making a switch, the best thing to do is ask an expert – many electricians and plumbers offer free consultations. Do some research and find one near you for an evaluation.

Before you convert your water heater’s fuel type to natural gas, there are a few things to consider. You can start by calling your local gas provider and asking whether they service your area. Some providers may even be able to give you an estimate of the costs right over the phone. Here are some other questions you should look into:

  • Is the fuel type available at your location?
  • How much will the installation cost?
  • Will the project require a permit?
  • Will you need to upgrade your home’s total amperage?
  • How much will your monthly bill be for this new fuel type?

You should be able to answer these questions after considering the following: Is it worth the time, effort, and money involved in changing your heater’s fuel type? Although changing your heater’s fuel type may need more work and money during installation, it may save you money in the long run.



Water heaters are only helpful if they produce hot water when needed. Whether the device has a tank or not, runs on gas or electricity, and whether it is more significant than your home’s water needs, it won’t work for you if it isn’t the correct size.

The electricity your heater uses also varies depending on the size of your unit. For example, storage water heaters come with 20- to 80-gallon tanks. The bigger the tank is, the more electricity it will need to heat the water.

A 40-gallon tank is usually sufficient for a 2- to 3-person household, but you should increase the size by 10 gallons for every extra person in your home. On-demand heaters are measured either by gallons per minute or flow rate. The higher the flow rate, the more power the unit will use at once, raising your electricity or gas utility bill.

To calculate the flow rate you will need for your home, add the flow rates of each fixture you want to run simultaneously. For example, if you wanted to shower, do laundry and run the dishwasher all at once, you would need to total the individual flow rates of those appliances.

You would then opt for a tankless heater with a greater flow rate than the one you calculated. Again, finding a balance between your family’s demands and the electricity available in your home regarding heater capacity is critical. Choosing a unit with the maximum power available may appear appealing, but it may require more amps than your home can handle.


Energy Efficiency

According to research, heating a home’s water consumes roughly 18% of the energy used by the residence. The number of amps consumed by your heater will be determined by how effectively it uses electricity. The more energy-efficient the heater is, the more amps it will require.

A new, more energy-efficient heater may require slightly more amperage to power it, but it will ultimately save you money because it won’t need to run as often. Frequently, older models are less energy efficient. So if your unit is over ten years old, investing in a replacement could be wise.

The energy efficiency ratings of electric water heaters are generally superior to those of gas units. However, because gas is frequently less expensive than electricity, the two options balance each other out in terms of cost. When looking for a new heater, look for the energy star logo. This sign indicates that the device meets Energy Star requirements. This equipment tends to be more energy-efficient and, as a result, cheaper.


Summing Up 

Thank you for sticking around till the end. We understand you’ve got many questions to be answered, so we appreciate your patience. Our team has done its best to answer some of the frequently asked questions about tankless water heaters and how many amps they draw.

And, if you appreciate our work and want to thank us, you can share this information with the people who require it. 

Read more on the topic:

  1. How Long Does a Tankless Water Heater Last?
  2. How Long Will It Take My Water Heater To Heat Up?
  3. What Causes Too Much Pressure in a Hot Water Heater?
  4. How Much Electricity Does A Tankless Water Heater Use?
  5. How Much Propane Does A Tankless Water Heater Use?
Mike Joshua

Mike Joshua, a 33-year-old plumber based in California. With a passion for solving complex problems and a commitment to his trade, Mike has dedicated the past 8 years of his life to honing his skills as a professional plumber. After completing technical college Mike quickly secured a job in a plumbing company and has been working steadily ever since. Mike's experience includes not only households but industrial gas and plumbing systems and installation, repair the equipment for different types of business He is known for his attention to detail, strong work ethic, and ability to complete projects on time and within budget. He is always striving to improve his skills and stay up-to-date with the latest industry developments and advancements. In conclusion, Mike enjoys outdoor activities such as hiking and camping. He also has a passion for DIY projects around the home and is always looking for new challenges to tackle.

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