Water Heater Sizes: A Guide

A water heater is an essential investment for any home. That being said, it's important to make sure you buy one that’s correctly sized in order to meet your family’s needs. Otherwise, you may be left without warm water for your morning shower more often than you'd like.

Water heater sizes: a guide

Today we'll explain the difference between the two main types of water heaters to help you choose the right one for your demands. We'll also provide you with an overview of popular water heater sizes and how to choose the right size for you.

Storage Tank or Tankless?

There are two primary types of water heaters: storage tank water heaters and tankless. Before finding the right size water heater, you must determine which type you’re going to purchase


A tankless water heater, albeit more expensive upfront, will provide you with hot water no matter what.

Tankless units work by using built-in coils to heat water when you need it, meaning you’ll always have hot water on demand. This makes these types of water heaters more efficient than traditional storage tank water heaters which could end up reducing your energy bills. The only catch? They provide a limited amount of hot water per minute. However, newer tankless units can support up to 9.8 gallons of water per minute simultaneously. This allows multiple showers at once!

  • More energy efficient.
  • Hot water on demand.
  • Offer a limited amount of hot water per minute.
  • Not ideal for everyone.
  • High upfront cost.

Storage tank

Storage tank water heaters are far more common than tankless. This type of water heater features an insulated tank that stores hot water until it’s needed.

We’ve all experienced the woes of running out of hot water, or waiting for water to heat up before jumping in the shower. These types of things happen because storage tank units have what’s called a recovery rise, or the amount of water they can heat in an hour. The more you depend on hot water in your home, the higher the recovery rise you’ll need.

  • Low upfront cost
  • Suitable for large households
  • Limited amount of hot water in a given period of time
  • Not as energy efficient

Water Heater Sizes

There are multiple sizes of hot water heaters available and you must determine your average water usage to help guide your decision on size. To further narrow down your search, you'll want to keep in mind a few key factors:

  • Your fuel source - Will you use natural gas, liquid propane or electricity for fuel? Or, will your water heater connect to your boiler? Determining this first will help you narrow down your options and make the shopping process much easier.
  • Physical size - Make sure you find a water heater that will fit in the designated space in your home.
  • Household size - Do you have a small condo or a large house? Is it just you and your partner, or do you have multiple family members? The size and occupancy of your household are some of the most important factors to consider when water heater shopping because you don’t want the last person showering to be stuck with cold water.

You’ll most likely need a higher capacity water heater to accommodate a household where multiple people shower, run the dishwasher, wash dishes with the faucet and do laundry at the same time, compared to a small condo where you just need hot water for one task at a time.

What Size Water Heater Do I Need?

If you’re going with a storage tank water heater, here’s a rough guide for storage tank capacity:

  • 1 - 2 people, you’ll need a water tank with at least a 30-gallon capacity.
  • 2 - 3 people, you’ll need at least a 40-gallon capacity tank.
  • 3 - 4 people, you’ll need at least a 50-gallon capacity tank (electric) or a 40-gallon capacity tank (natural gas or liquid propane).
  • If your family size is 5 or more, you’ll need an 80-gallon tank (electric) or a 50-gallon tank (natural gas or liquid propane).

Storage tank hot water heaters are sized based on BTU input and capacity in gallons. Again, the more you rely on hot water on a regular basis, the more BTUs and capacity you’ll need. For example, think about how many showers people take consecualty in your household. If you have 4 people each take a 10 minute shower all within a one hour period, you will use about 40 gallons of hot water. This can quickly empty the tank and it may not reheat quickly enough for other uses. All it takes is one person taking a longer shower for the tank to empty. Keep your daily routine in mind when make a selection of which tank size is right for you.

If you’re interested in going the tankless route, your shopping journey is a little bit different. Since tankless water heaters don’t store water, you don’t have to worry about capacity size. However, you still need to be mindful of two factors: Flow rate and temperature rise.

To determine the water heater flow rate needed, you'll want to add up the flow rates of all the appliances you plan to use at the same time (showers, washing machines, etc.). You'll then determine the necessary temperature rise by subtracting the incoming temperature from the desired outgoing water temperature. Ground water temperature can vary greatly across the county and at different times of year. Do some research and testing to see what your ground water temperature is before making a buying decision. For example, you can use 50 degrees Fahrenheit as the incoming temperature and 100 degrees Fahrenheit as the desired outgoing temperature. In this case, you would want a tankless water heater with a temperature rise of 50 degrees.

Based on average ground water around 50 degrees, here are the sizes you would need for a tankless unit based on your usage:  

  • 1 - 2 fixtures at once, you’ll need at least 3.5 GPM.
  • 2 - 3 fixtures at once, you’ll need at least 5 GPM.
  • 3 - 4 fixtures at once, you’ll need at least 7 GPM.
  • If your plan to use 5 or more fixtures at once, you may need multiple tankless units in sequence.

Making a Decision

We hope this guide has helped clarify the different factors and sizes you should consider before purchasing a new water heater. At Total Home Supply, we carry an assortment of both storage tank and tankless water heaters, all available with free shipping to anywhere in the contiguous United States. If you need additional assistance before making your purchase, contact us. Our in-house experts will be happy to help you find the right unit for your water heating needs.