How Much Power (Electricity) Does a Water Heater Use?

In today’s economy paying bills will almost always cause a headache, especially when it comes to electric bills. You’d be surprised how much money you spend on a water heating system. In fact, according to the Department of Energy, just under 20% of energy is used on water heating systems which means that you could drastically decrease your electricity bill by opting for an energy-efficient system.

When it comes to electric water heaters, electricity usage is dependent on both the size and the insulation of your water tank. For those who don’t know, an electric water heater is a device intended to keep your water warm or hot, and even though it works only 3 hours on average per day, it can affect your electricity bill.

So How Much Power (Electricity) Does a Water Heater Use? A typical water heater uses around 4,000 watts of power. If you run a water heater for 3 hours per day at a price of $.11 per kWh, it will cost you $1,32 per day, which is around $39,6 per month, and $475 per year. Most water heaters usually run between 3 to 5 hours per day.

The electricity usage of a water heater depends on the size of the tank and its Energy Factor (EF). An EF rating shows how much hot water heater can produce from a unit quantity. For example, if the water heater has a 30-gallon tank with an EF rating of 0.7, it will use 10-kilowatt hours (kWh) to produce 21 gallons of hot water per day (21 ÷10=2.1).

However, if your household consumes more than 2 kWh/day, you should consider replacing your current water heater with a model that has an even higher EF rating, such as 1.6 or 1.8. These water heater models are specifically designed for use in combination with the solar thermal system.

How To Calculate Water Heater Power Consumption?

Power calculation of water heater

The power consumption of every water heater depends on the size of the water tank and the desired heat temperature of the water. We’ve put together a calculation to help you better understand how much energy is needed for different sizes of water heaters.

Keep in mind that the power consumption of electric water heaters is usually between 400 and 3,000 kWh/year. The best way to get accurate data is to check the heater’s energy efficiency label. In order to find out how much energy your water heater use per hour, you will need to know the heating time and the power that is used.

Heater CapacityNumber of peoplePower ratingHeating timePower consumption (kWh)
8 gallons (30 liters)11,500 W55’1,375 kWh
13.2 gallons (50 liters)21,500 W1h30’2,250 kWh
21 gallons (80 liters)3-41,500 W2h15’3,375 kWh
26.4 gallons (100 liters)5-61,500 W2h50’4,245 kWh
Table: Shows the power consumption of different types of water heaters.

How To Get Power Consumption in kWh?

Power consumption calculation of electric water heater

To get the power consumption of a water heater, you need to know the power in Watts (W) and the heating time (t). By using these measures, you can calculate the electricity in kWh by following these steps:

  1. From W to kW: To get kilowatts (kW), you need to divide number in watts (W) by 1,000.
  2. To get heating time in hours: To get the heating time in hours you need to divide the minutes by 60. Next thing to do is to add these numbers to the hours.
  3. Multiply the power by the time: Multiply the heating time with the power in kilowatts (kW). That way, you’ll get the power consumption of your water heater in units of kWh.

The power consumption calculation with the same water heaters as in the previous section:

CapacityPower rating (kW)Heating time (h)Electrical Consumption (kWh)
8 gallons (30 liters)1,5 kW0,91 h1,375 kWh
13.2 gallons (50 liters)1,5 kW1,5 h2,250 kWh
21 gallons (80 liters)1,5 kW2,25 h3,375 kWh
26.4 gallons (100 liters)1,5 kW2,83 h4,245 kWh
Table: Converting power consumption from watts (W) to kilowatt-hours (kWh).

Calculating Energy Usage: Example

Energy calculation of water heater

If we assume that the water heater, on average, runs 3 hours a day and has a volume of 50 gallons, this is equal to 5,500 watts (5,5 kWh). By using the average electricity price in the US of $0.11 per kWh, this will cost us about $758 per year to run an electric water heater.

To find out how much electricity your heater uses in 1 hour depending on the temperature rise and the volume of water use the formula below:

Water heater volume (V) x hours (h) x temperature rise (t) / 3412 = Power

For example, if we raise the temperature from 10°C up to 65°C (55 degrees up) in a 26.4 gallon (100 liters) tank, the calculation will be:

  • 100 x 4 x 55 / 3412 = 6.4 kW
  • This means that your water heater will need 6.4 kW in 1 hour to heat the 100 gallons of water.

Getting a water heater with an EF of .98 rating could save you up to 20% annually on heating costs. Another great option for saving electricity is switching to a gas or a hybrid (gas/electric) unit. Some of these units are produced by companies such as Bradford White, GE Monogram, Vaillant, or Rheem.

How Much Power Water Heater Consumes In Idle Mode?

Due to the fact that the base temperature of water heaters is higher than the temperature of their surroundings, they start to cool down when they are idle. In order to prevent this and maintain the temperature of the water, water heaters use electricity even when they are not in use. This usage is expressed in kWh/24hr and is measured by the thermal dispersion at 65ºC.

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Usually, most water heaters have a thermal dispersion between 1 and 2 kWh/24hr. This means that heaters consume around 1 and 2 kWh every hour when they are in idle mode.

How Much Does It Cost to Run An Electric Water Heater?

To cost of running an electric water heater is usually between $0.3 and $0.9 per gallon. If an average person uses around 8 gallons (30 liters) of hot water per day, this will be between $3.7 and $8.2 per month. To simplify things, we have put together a table that will show you this for different types of water heaters.

Water Heater CapacityElectrical Consumption (kWh)Cost per gallonMonthly cost
8 gallons (30 liters)1,375 kWh$0,72$19,72
13.2 gallons (50 liters)2,250 kWh$0,52$23,42
21 gallons (80 liters)3,375 kWh$0.41$27,65
26.4 gallons (100 liters)4,245 kWh$0.31$26,31
Table: The real cost of running a water heater depends on the power and volume of the tank.

Cost Of Running A Water Heater For 24 Hours

Well, if we determine that most water heaters come with a 1,500 wattage, then it would cost you exactly $4.68 to run a water heater for 24 hours straight. The math behind this calculation is simple, 1500 (wattage) x 24 (hours) ÷ 1000 (watts to kWh) x $0.13.

Best Way To Measure Exact Power Consumption

Measure real power consumption by using Kill A Watt Meter

If you don’t feel like doing all these calculations yourself, don’t worry, we’ve got a solution! Kill A Watt meter is a handy little device that can help you determine the power consumption of any electrical appliance in the house. Just plug Kill A Watt meter in the wall socket, and connect the water heater to it. All electrical power that goes thrue that device will be measured, and you’ll know the exact power you are using in real-time.

Do Old Water Heater Raise Electric Bill?

Typically, most older devices such as water heaters, become less efficient over the years, leading to higher energy bills. That’s usually because the older water heater models vary greatly based on different factors. These factors are the age and size of the tank, temperature, how much water is used, and other variables. To avoid extra charges, you should stop using your old water heater, especially if it is over a decade old, and opt for a newer and more efficient model.

Related Article: How to Connect Multiple Bluetooth Speakers to One Device?

Can You Save Money By Turning Down Water Heater?

Turning down the water heater could potentially save you money. At least according to the U.S. Environmental Protection Agency. They claim that you could save up to 10%, which would amount to $41 annually (calculation done based on an average of $415 annually) by simply turning down the heat from 120 to 90 degrees.

How Much Gas Does a Water Heater Use?

Did you know that a gas water heater uses almost the same amount of energy as an electric heater? If you want to calculate this, use the following formula:

First, take the price you pay per therm, the number of hours your water heater operates, and the number of therms used per hour. To calculate your monthly bill, you should multiply these numbers.

Example: 3 (hours) x $1 x 0.205 (therms) = 62 cents. Furthermore, this would cost you $18 every month and $224 annually.

Gas vs. Electric Water Heater: Operating Cost

The main difference between water heaters

Typically, a gas water heater will cost you less money to run per month than an electric water heater. That’s because gas prices are usually lower than the cost of electricity in most states.

If you still think that the electric model is the way to go, be sure to get one with an EF rating of around 0.90 since those models are very efficient and won’t leave a dent in your wallet if you decide to get one.

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The same goes for gas heaters when it comes to EF ratings since a gas heater with a higher EF rating will use less gas than one with a lower rating. Keep these things in mind when you decide to get a new water heater.

Ways To Reduce Power Consumption Of Water Heater

As we’ve already mentioned, one of the best ways to save electricity is to lower the temperature below 120 degrees and keep it at that. This will lower your expenses, and you won’t have to reheat the water as often. Furthermore, you should opt for a more energy-efficient model, for example, one which has an Energy Star rating.  Lastly, here are other ways you can use to reduce water heater electricity usage:

  • Reduce the shower time
  • Make sure that your water tank is is insulated
  • Opt for a more energy-efficient water heater
  • Reduce the heating temperature of the water
  • Don’t get a bigger-than-necessary water tank
  • Invest in shower heads and faucets with the low-flow feature

If you are one of those people who care about energy consumption, then we advise you to read the article How Much Power (kWh) Does a Garage Door Opener Use?

Final Thoughts

Even though it is pretty unexpected, water heaters can really leave a dent in your wallet due to their age, size, the amount of hot water you use, etc. Thankfully, there are easy and quick fixes for this problem, such as investing in a newer and more efficient model, showering for shorter periods, opting for low-flow faucets and showerheads, or simply turning off the water flow while you’re brushing your teeth.

When it comes to any house appliance, you should try to invest in newer models and technologies to lower your electricity usage. The issues of older appliances that rely on electricity can especially become prominent during the colder months of the year when heating is even more necessary.

To avoid paying extra due to the energy inefficiency of your older appliances, think about getting your hands on more modern equipment.

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