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Water Heater Dimensions: What Water Heater Size Do I Need?

Written by

Rosanne Jones

Writer, Designer


Steven D. Carrico


water heater dimensions

Planning to purchase a water heater but wondering which of the available water heater dimensions will suit your needs?

Water heater sizes vary depending on whether you choose the storage tank or tankless type. The tank-style heater has options that can accommodate 20 to 80 gallons.

The average size the water heater can range from small (20 inches in diameter and 30 inches in height) to tall (21 inches in diameter and 50 inches in height).

On the other hand, a tankless water heater heats water when needed at an average rate of 2 to 5 gallons per minute. So which water heater should you choose? Read on to find out the best options available.

What Sizes Do Water Heaters Come in?


The measurements of water heaters are an important factor to consider especially if you decide on the tank style heater. Check out the most common water tank heater sizes and make sure the heater will fit in your home.

Water Tank Heater Diameter (in Inches) Height (in Inches) Capacity (in gallons)
Short/ low Boy 20 – 26 30 to 49 50
Tall 18 – 21 50 to 76 100
Narrow 20 16 30
Standard 20 40 40

Tankless Water Heater Sizes


Note that tankless water heaters are sized differently according to the maximum flow rate required or GPM (gallons per minute). These heaters work by heating water on demand and, therefore, do not need a storage tank.

Number of Fixtures used Simultaneously Size in GPM (Gallons Per Minute)
1 to 2 3.5 GPM
2 to 3 5 GPM
3 to 4 7 GPM

Dimensions of Water Heater Vary on Capacity

A good way to determine the best water heater tank size is by basing it on the number of people in the household.

  1. For a family of 3, a tank capacity ranging from 23 to 36 gallons will suffice.
  2. For a family of 4, you will need a larger tank of up to 56 gallons
  3. Just like that, for a family of 5, an additional 10 gallons per person is added. , making it 66 gallons.

Let’s discuss the most common water heater capacitiess and some top brands.

1. 30 gallon water heater capacity


A 30-gallon water heater is the smallest type of water heater tank you can find on the market. These fall under the category of “low-boys” and are considered the shortest type of water tank heater. Their compact size and efficiency make them ideal for smaller households.

Water Heater Brand/ Model Width (In) Height (In) Length (In)
Bosch Thermotechnology Tronic 5000T 18.25 48 18.25
Reliance 6-30-EOMSS K100 20 39 20
Rheem 72-30-2 240V 22 48 20

2. 40 gallon water heater capacity


The measurements of the 40-gallon water heater are similar to the 30-gallon water heater; however, 40-gallon water heaters are taller by a few inches.

 Water Heater Brand/ Model Width (In) Height (In) Length (In)
Bradford White RG40T6N 20 60.5 20
Reliance 6-40-NOCT 400 21.13 61.81 1
Duda Solar ‎tank151 18.5 59.06 ‎18.5

3. 50 gallon water heater capacity


These average-size water heaters are a good choice for medium-sized families with three to four members. The water heater width for 50-gallon capacity heaters may vary from medium water heaters to narrower designs ideal for compact spaces.

Water Heater Brand/Model Width (In) Height (In) Length (In)
Rheem Professional Classic Series 20.25 61.63 20.25
Bosch Thermotechnology Tronic 5000T 20.25 59.75 20.25
Bradford White BWC RE350T6 22 60 22

4. 60 gallon water heater capacity


These heaters feature only 10 gallons more capacity compared to the 50-gallon water heater. Although the diameter of the water heater is a few inches wider than the 50-gallon heater, the difference is negligible.

Water Heater Brand/Model Width (In) Height (In) Length (In)
HTP SSU60 290104 23.25 52.5 23.25
Rheem Professional Classic Series 20.25 61.63 20.25
Rheem G100-200 Natural Gas 30.25 66.12 30.25

5. 80 gallon water heater capacity


The average water heater height of an 80-gallon tank is nearly 70 inches making it the second largest type of water tank available. The measurements of this water heater enable usage for families of more than five with considerable water usage habits.

Water Heater Brand/Model Width (In) Height (In) Length (In)
American Standard Water Heaters D-80-199-AS 28.25 68.25 28.25
ProLine® Electronic Thermostat Electric 26 64.5 26
A.O. Smith Signature 900 27 69 27

6. 100 gallon water heater capacity


The 100-gallon water heater capacity is the biggest water heater tank that is often used for commercial purposes. Weighing over 150 kilograms, the 100-gallon water heater is too bulky for residential use.

Water Heater Brand/Model Width (In) Height (In) Length (In)
Rheem G100-200 Natural Gas 30.25 66.12 30.25
American Standard D-100-270-AS 30.25 73.625 30.25
American Water Heater Company HCG3100T1993P 27.75 86 27.75

How Much Space is Needed for Water Heater Installation?


You need to consider both the clearance space and how wide your floor area is before selecting a water heater.

  1. Ideally, the clearance space should be a minimum of 6inches of space around. However, natural gas water heaters require air circulation, so additional space is required.
  2. For an electric water heater, an additional 3 ft clearance from the floor and a foot from the rear is necessary.
  3. Tankless heaters should also have a 12-inch clearance from the back and be at least three feet off the ground.

You may refer to the manufacturer guidelines for details on clearance.

What Size Water Heater Do You Need?


There are two ways to determine the size of the water heater you need:

  1. Your family size: For instance, a family of three with minimal water consumption could easily use a 30-gallon water heater. However, this would not suffice for a larger family with multiple bathrooms and fixtures.
  2. Using the first-hour rating: this tells you how much hot water your heater can produce each hour. Purchase a water heater that has a capacity closest to this amount.

To calculate the first-hour rating:

  • Select the hour when you use the most water
  • Use a calculator to determine water consumption per activity
  • Total the quantities to get the first-hour rating


As we have discussed, water heater dimensions vary depending on capacity which in turn depends on your water consumption needs.

We hope this guide answers all your questions on finding the best water heater. Let us know if you have any other questions.

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