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What Size Water Heater Do I Need?

Do you feel like having a new tank or tankless water heater for your home? If that’s your plan, then it’s good to ask yourself “what is the right water heater size I need for my home?” This question is important for making the right decision.

Choosing the perfect size can make a huge difference when you consider your utility bills and comfort. Using a smaller propane tankless water heater or an electric tankless water heater can ruin shower time. Installing a bigger tank attracts more bills, so you need to ask what size water of heater do I need?

Capacity Measurement of a Water Heater

Before anything, find out the capacity of a water heater. Countries like the United States measure in gallons, so water heaters come in 40 or 60 gallons measurements. Depending on where you are, other countries use liters as the standard measurement for water heaters.

Tank Water Heater Sizing Guide

Getting the perfect size of a tank water heater can be a stressful job. Here are two ways to get it right.

  • The amount of water you need for the whole family
  • The number of gallons of water that goes into a tank every hour

Before we reveal to you details on sizing tank water heater, you can use this chart below to make a better decision.

Tank Water Heater Sizing Guide

First, it is good to find out how much water you need in your home. The outcome will help make a better calculation of the volume of water that will serve everyone.

You’ll need to consider the times and places where you use hot water. For instance, after two family members have a shower, do you start the washing machine? If that is what happens, then a total of 72 gallons of water is being used at that moment.

The only way to get through without problems is to have a water heater that lasts an hour. That means you need a tank water heater that can contain 50 gallons and a first-hour rating (FHR). A tank of 40 gallons may appear big, but it doesn’t have a high FHR, therefore avoid it.

A family of four will make use of about 200 to 400 gallons of heated water per day. This usage includes washing, cleaning, laundry, and dishwashing. A couple without kids will need half as much while a family of six requires around 600 gallons a day.

You base the size of the water tank on the amount of water you use each day, not on family size. Some family members use more water than others, and the distance of the water heater can affect volume too.

Large houses where some rooms are far from each other will need a bigger tank. This issue is different in a home where the usage of hot water takes place within the same area of the home.

Sizing a Tankless Water Heaters

The tankless water heaters are especially good for larger families. It saves cost and time and makes it easier to draw water from more than one source at once. Also, it is compact, which means you can hide them from public view, unlike some other models.

There are two ways to measure tankless water heaters. These are:

  • The amount of water that you will use in every minute
  • The degree of heat the water needs to reach before use

Since the tankless water heater is measured in gallons, always keep in mind “what size hot water heater do I need?” Below we have created a chart to make things easier for you.

Sizing Guide for Residential Tankless Water heater

Household Occupants


Capacity Required

(Measured in Gallon)

Electric Gas
 1-2 people Regular/ Low 30



40-50 40-50
 2-3 people Regular/Low 40



50 40-50
 3-4 people Regular/Low 50



80 50-75
5+ people Regular/Low 80





You can also get the perfect size for the whole family using these three steps.

  • Calculate the quantity of water simultaneously used by everyone and everything in the home. If you will take a shower and at the same time turn on the washing machine, put that into consideration. Calculate around 1.5 to 2 gallons per minute shower time and about 3 or 4 gallons for dishwasher or washing machine.
  • Where you live at the time also matters if you want to get the right calculation. If you find yourself in the northern part of the US, you need to purchase a stronger tankless model. The reason is that it takes a longer time to heat up water due to the cold climate in the area.
  • The important thing is that you get the amount of water usage and the right temperature for the tankless heater. The next thing is to find a tankless heater that is perfect for your home. Most manufacturers provide detailed information online, and you can check them out before making a decision.

Whether you choose a tank or tankless water heater, think of your long term needs. You may have a smaller family now but plan to have a bigger family in the future. That means you will purchase a size that serves you currently and better in the long run.

Solar Water Heating System Sizing Guide

If the solar water heating system is your ideal choice, you need to get your calculations right, especially during the summer. Two important factors are the total collector area and meeting 90 percent to 100 percent of household water needs.

Solar system workers often use computers and worksheets to determine collector size and system requirements. Here is a chart below that will help you make the right decision.

Sizing For Residential Solar Hot Water Systems

Household Occupants/Property size

Flat Plate Collector

FK series

Solar Cylinder Capacity

( Measured in Liter)

1-2 people in 1 Bedroom Apartment 1 x FK 250

(1.88m2  aperture Area)

180 liter

 1-3 people in 1-2 bedroom apartment

1 x FK 500

(2.35m2 aperture area)

210 liter

3-4 people in 2-3 bedroom Apartment

2 x FK 250

(3.76cm2  aperture area)

250 liter
4-5 people in 3-5 bedroom apartment 2 x FK 500

(4.70m2 aperture area)

300-400 liter

6+ people in 5-6 bedroom apartment

3 x FK 250

(5.64m2 aperture area)

400 liter

This chart is for determining the size of solar hot water system. Keep in mind that most solar unit can last for 15-20 years so consider the bedroom number in case of future addition or changes.

For collector area

For collector area

The standard size most solar contractors follow is 20 square feet for the first two members of a family. For other members, another 8 square feet each is added if you live in the US. That means 12 to 14 square feet for those in the northern part of the States.

Storage volume

Storage volume

Tank of 50 to 60 gallons should be enough for two to three people. An 80-gallon tank can comfortably serve a family of three or four persons. Four or more people should go for one with a larger storage volume.

The increase in the size of the collector means an increase in the size of the solar storage tank. The 1.5 gallon for each square foot keeps the tank from overheating when there is a low demand for hot water. In sunny and warm climates, experts suggest that 2 gallons per square foot are ideal at that time.

Other calculations involved are to evaluate the source of solar power and the proper tilt for the solar collector. If you don’t understand how to do it, read it up on the solar heaters page for more instructions.

Other Things to Consider to Get the Right Size

You may find that it isn’t easy to get the heater that best serves the needs of the home. While you may have your personal preference, it is good to look out for the following specifics.

  • Fuel Source: Decide if you are going to use electricity, a boiler, liquid propane, or gas to heat up your tank. This fact check will guide your selection and purchase of the perfect water heater.
  • Physical Size: Make sure the product you buy will fit well in the space you have prepared for it.
  • Household Size: Before asking what size water heater do I need, consider the size of your family. The size you’ll need when it’s just you and your partner will not be the same as when you have a large family. People who live with you determine the kind of heater you will have to buy.

Families where people wash dishes, do laundry, and shower at the same time will require a higher-capacity water heater. It is an entirely different scenario in a small family that uses water for just one task at a time.

Types of Water Heater

Before you do that shopping for the right water heater size, you may want to know the different types. Here is a list of what you may find at your local shop.

Storage Tank Water Heaters

Storage Tank Water Heaters

This water heater is common in most stores. They are big and can heat, store, and disseminate large volumes of water around the home. They need constant power to retain water at a temperature close to 120 Fahrenheit all the time.

The downside side to tank size is that small tanks store water enough for household use. If you get a tank too big for the home, you’ll be heating up the water you don’t even need.

Tankless Water Heaters

Tankless Water Heaters

Unlike storage-tank type, tankless water heaters do not work with tanks. They heat water when you need it and only when you turn on the faucet. That is why they are also called instantaneous or on-demand water heaters.

They save you money and energy and eliminate time spent on heating and storing large volumes of water. However, if rooms are far from the unit, you have to get more than one tankless heater.

Hybrid Water Heaters

Hybrid Water Heaters

Hybrid water heaters are more energy-efficient, which means lower electric cost. They function by sucking in the heat within the environment through their heat pumps. These heaters come with inbuilt water tanks or added to tanks already in use.

Point-of-Use Systems

Point-of-Use Systems

This heater is divided to allow each unit to be installed in a closet or right under a sink. It can deliver the required hot water as fast as it is needed to a specific location.

Final Word

The question of what size water heater do I need is the first step to getting the right water heater. It guides you throughout the process of selecting and buying the right type and size of the water heater. Your family size and space will make it easier to determine the water tank to choose from available options.

Keep in mind this following step to having the perfect water heater:

  • Check how many gallons a tank can produce in an hour
  • Find a water tank size that best meets your household needs
  • Consider your family size and space when shopping for the perfect water heater

If you have any questions, use the comment section, and let’s hear what you have to say.