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What Size Water Heater Do I Need?


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Finding the right sized water heater to meet your household hot water needs should be your number one priority when shopping for a water heater. But there's also other things to consider, including the energy efficiency of the appliance.

This article will help you find the right sized tank-style water heater and provide you with the information and resources to help you make an educated buying decision.

Pen and Paper with Calculator

Finding the Right Sized Water Heater

Tank-style water heaters heat water and store the hot water within a tank until there's a demand. A water heater with a larger tank will obviously be able to deliver more hot water.

There are several ways to determine what size water heater you need to buy. The simplest method is to use the chart below, but it's important to understand that these numbers are only an estimate and your individual hot water needs may vary.

If you're considering purchasing a tankless water heater, you may want to check out our tankless water heater calculator.

Water Heater Sizing Chart

Household Members

Recommended Tank Size

2 People

45 to 55 Gallons

3 People

55 to 65 Gallons

4 People

65 to 75 Gallons

5 People

75 to 85 Gallons

6 People

85 to 100 Gallons

7 People

100+ Gallons

Remember this chart is not exact, in fact some sources estimate higher tank sizes. As an example, a 30 to 40 gallon tank may be more than enough hot water for a household of two, or you may need a 45 to 55 gallon tank.

However, it's safer to error on the side of purchasing a larger water heater (within reason), then to risk constantly running out of hot water. Plus, if you have a growing family, your new water heater will be able to handle the extra demand.

Stop Watch

First Hour Rating Method of Sizing

A more accurate method of sizing a water heater is to use the first hour rating method. Many homeowners prefer this method since you'll purchase a water heater that more closely meets your hot water needs.

Buying the right-sized water heater is important because:

  • If the water heater is too small, you'll frequently run out of hot water. Your water heater may also be prone to breaking down and have a shorter service life since it will be overworked.
  • If the water heater is too large, your utility expenses will be higher than necessary. This is because you'll be heating and holding hot water that you don't need. If you have an 80-gallon water heater, but only use 50-gallons, you'll have paid (in utility costs) to heat and hold 30-gallons of water that is never needed!

In order to use the First Hour Rating Method, you'll need to know your household's Peak Hour Usage and the water heater's First Hour Rating. Here's what to do:

Peak Hour Usage

In order to estimate your peak hour demand you'll need to determine the hour of day when your household uses the most hot water. 

For most households, the peak demand is in the morning when everyone is showering and preparing for the day. But your peak hour may be different, so you'll need to pay attention to your family's hot water routine.

Then, estimate the maximum hot water used during this one-hour time period. Count how many showers are run, loads of laundry, dishes washed, etc. Use the below chart as a reference:

Hot Water Source

Average Gallons Used

Shower / Bath

20 Gallons

Handsink / Shaving

4 Gallons / 2 Gallons


14 Gallons

Washing Machine

32 Gallons

As an example, if your household used 2 showers and 1 hand sink, your peak hour usage would be 44-gallons. (20 + 20 + 4 = 44).

First Hour Rating

Now that you know your Peak Hour Usage, it's time to consider the water heater's First Hour Rating.

The First Hour Rating is defined as the number of gallons of hot water the water heater can deliver per hour when it has a full tank of hot water. These factors impact a water heater's first hour rating:

  • Size of tank
  • Fuel source (gas or electric)
  • Size of the burner (gas) or element (electric)

Look on the water heater's yellow EnergyGuide label (top left corner) to find the First Hour Rating (it may also be listed as Capacity or FHR). 

Using the example above, your Peak Hour Usage is 44-gallons, so you'll want to find a water heater with a First Hour Rating of at least 44-gallons.

It's a good idea to purchase a water heater that is at least a few extra gallons above your First Hour Rating to play it safe.

Watch the Video

This video goes through how to determine what size water heater you need to purchase, plus some other good suggestions.

Questions Marks

Other Considerations

Once you know what size water heater you need, there are a few other things to consider before buying. 

Gas or Electric

The majority of tank-style water heaters are either fueled with natural gas/propane or electricity. Gas water heaters use a burner to heat the water, where an electric water heater uses one to two heating elements.

Both gas and electric water heaters have their advantages and disadvantages, so if you're able to make the decision, you'll want to do your research. Although, more often than not, the decision will already be made for you.

> > Learn more about the differences between gas and electric water heaters < <


If you're installing your water heater in a large space, such as a garage or basement, you shouldn't need to worry about having enough room. However, in many cases water heaters are installed in closets and other tight spaces.

When this is the case, you'll need to consider the dimensions of the water heater. As you might guess, a 80-gallon tank is going to be larger than a 50-gallon tank. Fortunately, manufacturers recognize you may have special installation requirements and have a variety options.

If height is a challenge, you may want to look into a short water heater (sometimes called low-boys). These water heaters are shorter and wider than standard, so they often fit into tight spaces where a standard size simply won't fit.

There are also narrow water heaters that are taller and narrower than standard. Both of these are great options as they do not require you to compromise on tank size, since the adjustment was made by the dimensions of the water heater.  

> > Learn more about water heater dimensions < <

Energy Factor (EF)

Each water heater sold in the United States is required to have a yellow Energy Label visible to the consumer. The Energy Label allows you to easily compare one water heater to another in regards to their operating costs and energy efficiency.

Look for the energy factor rating (EF) on the EnergyGuide Label to see the water heater's efficiency.

The higher the EF rating, the more efficient the water heater.

Don't be surprised to see the price of the water heater increase with the more energy efficient models. But since they'll run more efficiently, you'll recoup the additional purchase price in operating costs. 

If at all possible, purchase a water heater that has earned the ENERGY STAR label. These appliances have meet the government's strict standards of energy efficiency, and they'll save you money in the long run.


All water heaters come with the basic components to heat water, but there are some basic features you may want to consider:

Brass Drain Valve - Many water heaters come with inexpensive plastic drain valves that can easily crack or break when trying to drain your unit for routine maintenance. Although you can always replace your drain valve, having a brass one from the start saves you the hassle.

Glass Lined Tank - Water heater tanks are made from steel, so they are prone to rust and corrosion. Manufacturers often line the tanks with glass to help protect the tank and reduce corrosion. Although, not a fool-proof method from preventing your water heater from leaking, it will typically add years to its service life.

Dry-Fire Protection - If you're purchasing an electric water heater, you may want to consider dry-fire protection. This technology will sense when there isn't water around the upper heating element and prevent it from firing. When a heating element fires without being submerged in water, it will burn out.


The majority of people glance at the warranty and don't look past the number of years of coverage. We recommend digging a little deeper. Reading reviews online is helpful, but don't be afraid to do your own research.

Check to see how a claim is filed, is the warranty void if you install the unit yourself, and what is and isn't covered. 

In most cases, if you're looking for the cheapest water heater, you'll also get a less than stellar warranty. You get what you pay for . . . and that includes the warranty.

The majority of water heater warranty's run between 3 to 12 years. Manufacturers tend to put better warranties on their higher quality water heaters.

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