How Many Watts Does a Hot Water Heater Use?

Last Updated On June 12, 2024

Updated on November 16, 2021



Reviewed by

how many watts does a water heater use

How much electricity does your electric hot water heater use in watts and kilowatts? 

You know that your electric hot water heater uses a certain amount of electrical power, or watts, to heat up the water in your home, but did you know your electric water heater makes up for around 14% of your home’s electricity usage

Since your water heater makes up such a high percentage of your electric bill, it can benefit you to learn how to calculate the energy usage of your electric water heater and cut water heating electricity expenses. 

In this PlumbingNav guide, you will learn:

  • How to discuss electricity usage
  • Average water heater electricity usage
  • How to calculate water heater electricity usage
  • How to lower electric water heating costs 

What's In This Guide?

      What You Need To Know About Calculating Power Use

      Before we go into the details of calculating your electric water heater’s power usage, we should cover some of the basics, such as terminology and how electricity works in your home. 


      Refer to this section throughout this guide if you run across any unfamiliar terms.

      • Circuit – electrical current that supplies a device with power
      • Circuit Breaker – control center for all the circuits running through your house
      • Flow Rate – Speed at which a water heater provides hot water measured in gallons per minute (GPM) 
      • KIlowatt – 1000 watts
      • Uniform Energy Factor (UEF) – efficiency rating
      • Volt – measurement of the force of the current
      • Watt – measurement of electrical power

      How Electricity Heats Your Water

      We will cover how both tank and tankless water heaters work and the pros and cons of both. 

      Tank-Stye Electric Water Heaters 

      Standard 240-volt residential tank-style electric water heaters use a dual-heating element design for optimal efficiency. Each element has a thermostat attached to it set to a specific temperature (most often 120° F). 

      The heating elements will activate when the water isn’t the temperature set on the thermostat, using electricity. The lower element activates first, heating its portion of the water. The lower element then turns off, and the upper element heats the remaining water. The heating elements continue to run to keep the water in the tank warm. 

      Pros of tank-style electric water heaters:

      • Less expensive upfront cost
      • Simple operation (low maintenance and repairs)
      • Multiple appliances can use water from the tank until the water becomes depleted

      Cons of tank-style electric water heaters:

      • Higher electrical bills
      • Requires more space
      • Shorter life span

      Tankless Electric Water Heaters

      Standard 240-volt residential electric tankless water heaters heat the water on demand when someone turns on the faucet, activating the heating elements. When the faucet turns off, the unit turns off shortly after. 

      This option uses far less electricity since the unit doesn’t have to constantly keep the sitting water in the tank warm. 

      Pros of tankless electric water heaters:

      • Lower utility bills
      • Longer life expectancy
      • Space-saving small size

      Cons of tankless electric water heaters:

      • Higher upfront cost (both the unit and installation)
      • Requires more maintenance
      • Many do not accommodate multiple units at once
      did you know how many watts does an electric water heater use

      How To Calculate The Watts Your Water Heater Requires (5 Steps)

      Knowing how many watts your current electric water heater uses can help you make decisions about water heater purchases and how you use your water heater. 

      Use this simple 5-step guide to determine how many watts your water heater is using. 

      Step 1: Estimate the Amount of Time Water Heater Runs Each Day

      Your tankless water heater runs any time you turn on the faucet. Electricity powers your water heater until you shut the faucet off. This adds up quickly, especially when you take into account longer showers and washing machine/dishwasher use.

      Tank units run even longer every day since they must heat the cold water that comes into the tank. Then, the unit must heat the water that replaces the water you used. 

      If you are unsure how much time your water heater runs each day, calculate how much hot water you use per day using the following estimates:

      • 8 minute shower – 16 gallons
      • Full tub – 36 gallons
      • Dishwasher – 6 to16 gallons
      • Laundry machine – 25 gallons
      • Sink usage – 1 gallon

      Once you determine the gallons you use per day, determine the flow rate of your unit to determine how long the unit runs to meet your needs. 

      Step 2: Find Volts and Wattage on Device 

      Your electric water heater should clearly label how many volts it uses and how many watts each element uses on the device itself or in the user manual. Most residential dual-element water heaters run on 240 volts. The wattage depends on the voltage. 

      How do you know the voltage of your electric water heater? All water heaters come with a set voltage. Read your manual to double check the exact voltage of your unit. 

      After you confirm the voltage, check the wattage of the unit. Don’t forget to find the wattage for both heating elements! Do not add the wattage. Instead, use the “Total Watts” total on the sticker (most of the time they will use the same wattage). 

      Step 3: Use kWh Formula to Determine Wattage Usage

      Use the following formula to determine the wattage your unit uses per day:

      (Heater Watts x Operating Hours Per Day) / 1000 = Daily Electricity Usage (kWh)

      The formula is quite straightforward. You take the wattage of the unit and multiply it by the amount of time it operates. After that, you divide the number by 1000 to convert the figure from watts back to the more standard kilowatts (remember that 1 kWh = 1000 watts). 

      For an example, let’s calculate hypothetical water heater usage using the ultra efficient Rheem Professional RTEX-18 electric tankless water heater.

      In the product spec sheet, we see that this model operates at 240 volts and 18 kWh (or 18,000 watts) and has an efficiency rating of .95. Let’s assume that the family runs the water heater for two hours a day (the average for tankless units). 

      (18,000 x 2) / 1000 = 3.6 kWh/day

      This comes very close to the national average of 4,000 watts (4 kWh) per day. Multiply the daily usage by 30 days to get your monthly usage and 360 to get your yearly usage (108 kWh and 1,296 kWh, respectfully). 

      Pro Tip: Don’t want to calculate the wattage yourself? Get a smart water heater equipped with WiFi and Bluetooth connectivity that sends you reports on usage and helps you use your device in the most efficient way possible. 

      Step 4: Calculate Electrical Cost of Water Heater

      Most people want to learn how many watts their water heater uses to determine the electrical cost of the unit. Now that you know the electrical consumption of the device, you need to find the rate of electricity in your area. 

      Since most electricity rates are in kilowatts, make sure to multiply it by 1,000. Then, use the following formula to calculate electricity cost per day:

      (Daily kWh ÷ UEF rating) x Fuel Cost = daily electricity cost

      If we use the national average electrical cost of $0.1329 per kWh with the example we used above of 3.6 kWh per day and a .95 UEF rating, that household can expect to pay $0.50 per day. This leads to roughly $183 per year in water heater electricity cost.

      Step 5: Reduce Electric Water Heating Costs

      Now that you know the electrical usage of your device and the cost to operate it, you should take action to reduce your water heating costs. 

      Start by buying a hybrid or electric ultra-efficient water heater with an EnergyStar sticker. However, some EnergyStar units work more efficiently than others.

      How Do You Reduce Electric Water Heater Costs?

      All water heaters have a Uniform Energy Factor (UEF) that rates their efficiency. The higher the UEF, the more efficient the unit. The most efficient units have a .95 UEF, but any product with a .90 UEF or higher will show significant savings on your bill. 

      If you want to make the most of your current water heater, use these simple tips to reduce your electric bills while still enjoying hot water when you need it:

      1. Limit Hot Water Use

      You can change household habits to reduce the amount of hot water you use. According to the EPA, letting the water run when washing dishes by hand wastes enough energy to power a 60-watt lightbulb for 60 hours. 

      Try shutting off the water when you don’t need it, taking shorter showers, and drying your clothes outside. 

      2. Set Thermostat Lower

      As we briefly mentioned earlier, most houses have the hot water heater set to 120° F. This temperature keeps water hot while still preventing scalding. Turn the temperature down on your water heater a couple of degrees to save energy. 

      You can change the temperature on your electric water heater yourself rather simply, even on models that don’t have simple control panels or mobile phone apps. 

      3. Perform Regular Maintenance on Water Heater

      Both tank-style and tankless electric water heaters require regular maintenance about once a year, especially as they get closer to their life expectancy. 

      For tank-style electric water heaters, flush the tank and refill it to help eliminate any sediment build-up in the tank. 

      Tankless water heaters require more experience to maintain and may require a professional, but the process involves cleaning the unit and getting rid of any sediment build up. 

      SAFETY FIRST!: Always shut off the power to your electrical water heater at the circuit breaker before performing maintenance on it. 

      4. Use Low-Flow Fixtures and Appliances

      Showerheads with a WaterSense label cannot exceed a flow rate of 2.0 GPM, many of them even lower. You can also buy energy efficient dishwashers, dryers, and washing machines that use less hot water. Just look for the EnergyStar sticker!

      Final Thoughts on Calculating Electric Hot Water Heater Wattage

      Most residential electric water heaters use about 4,000 watts of electricity a day and cost $450.00 per year to operate

      Of course, this varies based on:

      • needs in your home
      • your habits
      • the water heater efficiency
      • maintenance
      • technology available
      • cost of electricity

      FAQ About Electric Hot Water Heater Wattage 

      How many watts does a 40-gallon hot water heater use?

      A 40-gallon hot water heater uses around 4,500 to 5,500 watts.

      Can I plug my hot water heater into my generator?

      Depending on the total wattage rating, your generator could be used to run your hot water heater. Just make sure the total plugged into your generator does not exceed the rating.

      A generator with 7,500 to 10,000 watt capacity will be a safer bet than 5,000 since most water heaters need at least. 3,500 to 4,5000 watts and a higher-capacity generator will allow you to run multiple appliances at the same time.

      Will a 5000 watt generator run a hot water heater?

      In general, a 5000 watt generator should be able to run an electric water heater. However, be very cautious to not exceed the total wattage rating of the generator. Since an electric water heater needs about 4,500 watts to start up and 3,500 to continue being powered, the wattage uses should be monitored closely.

      Meet Your Plumbing Navigator

      Plumbing Navigator: plumbing advice

      About Plumbing Navigator

      We’re passionate about all things plumbing, and love sharing tips, “how-to”, and reviewing the latest products to help make your project a success!

      Learn More Plumbing Tips

      Want to tackle more plumbing projects? Check out these helpful guides!

      best water heater stand
      tankless water heater flush kit
      best mesh drain strainer
      Best Shower Drain Cover

      Got Plumbing Questions? Search For In-Depth Answers Below!

      About Plumbing Navigator

      We write about "all things plumbing," helping you navigate common questions, repairs, and the best plumbing products on the market.

      About Plumbing Navigator

      We write about “all things plumbing,” helping you navigate common questions, repairs, and the best plumbing products on the market.

      Recently Published Guides