How much electricity does an electric water heater use?
The amount of electricity that an electric water heater will use depends on a number of factors, including its size of the water tank, the temperature it is set at, how much water is used and how energy-efficient the model is.
However, you can find out how much electricity a specific system consumes by checking its nominal output. This is usually given in kilowatts (kW) or watts (W). Modern, energy-efficient instantaneous electric water heaters have a nominal output of up to around 10 to 12 kW. This means that, depending on the water heater you go for, they would consume between 10 to 12 kW per hour. To figure out how much this would cost you, you would need to find out how much your energy company charges you per kilowatt hour (kWh). The average price per kWh is approximately 14.37p. You would need to multiply the nominal output by the price per KWh to figure out how much electricity your system would use per hour.
Here are some example calculations:
If you opt for a 10 kW water heater:
10 kW x 14.37p per kWh = £1.44 per hour to run
If you opt for a for a 12 kW water heater:
12 kW x 14.37p per kWh = £1.72 per hour to run
If you opt for a new, energy-efficient wall-mounted electric storage tank to generate and store hot water, you can expect it to have a nominal output of between 2 and 6 kW. Using the average price per kWh (14.37p), you could expect to pay between 28.74p and 86.22p per hour for running this system.
Of course, the actual amount you’ll pay per month will depend on the amount of time you run your water heater for and this will depend on your personal consumption and how busy your household is. However, if you opt for a modern system with a high energy efficiency rating, you can expect not to have to run your heater as much as you would if you choose an older or less efficient model.
In a lot of cases, it is useful to know exactly how many watts water heaters use. If you want to run a water heater using a generator or estimate electricity costs, you will need to know the water heater wattage. How to check how many watts does your electric water heater draw? Just check the label on the tank. You will find the specified
wattage for your water heater, ranging from 1000 watts to over 10,000 watts if you have a very big hot water tank. Note: If you find 2 wattages
(4500W and 4500W, for example), this doesn’t mean water heaters require 9000 watts of electric input to run. These are water heaters with two heat exchangers (to increase efficiency expressed as UEF) but it is important to understand that both don’t come on at the same time. You will still only need a generator that can generate 4500 watts to run such a water heater.
Even if you don’t find the label, you can quite easily determine water heater wattage by boiler capacity like this:
A lot of water heaters actually use the same heater size: 4500 watt heater. This is best illustrated with roughly 3 categories of water heaters:
- Smallest 10-gallon and 20-gallon heaters use anywhere between 1000 watt and 2000 watt heaters that run on a 120V circuit. A 1600 watt 120V heater is the standard heater for these smaller water tanks.
- Majority of water heater sizes (30-gallon, 40-gallon, 50-gallon, 60-gallon, 70-gallon, and 80-gallon) use the standard 4500 watt heater that runs on a 240V circuit. That means that the most common water heater wattage is 4500 watts.
- Biggest 90-gallon, 100-gallon and 100+ gallon heaters can use high-wattage heaters beyond 4500 watts. It is not uncommon to see a 10,000 watt heater for a 100-gallon water tank.
Here is the full table of how many watts do hot water boilers use when operating at 100% heating output:
| Water Heater Size: | Wattage: |
| 10 Gallon Water Heater | 1000 – 2000 Watts |
| 20 Gallon Water Heater | 1000 – 2000 Watts |
| 30 Gallon Water Heater | 4500 Watts |
| 40 Gallon Water Heater | 4500 Watts |
| 50 Gallon Water Heater | 4500 Watts |
| 60 Gallon Water Heater | 4500 Watts |
| 70 Gallon Water Heater | 4500 Watts |
| 80 Gallon Water Heater | 4500 Watts |
| 90 Gallon Water Heater | 4500 Watts Or More |
| 100 Gallon Water Heater | 4500 Watts Or More |
As you can see, most water heaters will require 4500 watts to run at 100% output.
Example: How many watts does a 50-gallon water heater use?
If you check the table above, you can see that the standard 50-gallon water heater uses 4500 watts of electricity.
Even smaller 30-gallon and 40-gallon heaters will use 4500 watt heaters. However, 20-gallon water heater will use anywhere from 1000 watts to 2000 watts of electricity.
This has an interesting effect:
Water in smaller 20 gallon water heater will warm up slower than in the bigger 30 gallon water tank. That’s because the difference in amount of water is 50% but the difference in the electric heating input is more than 100% (2000 watts vs 4500 watts).
It is also important to note that standard 4500 watt heaters run on an upgraded 240V circuit. The smallest water heaters (10-gallon and 20-gallon) usually require only the standard 120V circuit.
We hope this adequately illustrates how many watts do water heaters use. Based on the water heater wattage you can also size a generator for running a water heater in the event of a power outage.