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Complete Guide On Water Heater Sizes

Last Updated: 14 May 2020

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Water heaters play crucial roles domestically, making them an essential appliance for each home to invest in. This is why the purchase of a sufficiently-sized water heater is crucial to meet your family’s needs. Otherwise, you’d run out of hot water far often than you want.

Although basic, the task of choosing the right size of water heater can be complicated of you aren’t armed with relevant information before setting out to make the purchase. Besides its direct relevance to the fulfillment of your household’s heated water needs, this same choice has got much to do with your utility bills too. So, you need to think long and hard about this before tapping that purchase now button.

Herein, we’ll explain everything you need to know about the best water heater sizes and how to size a water heater, so you can make informed water heater purchase choices.

What is the Capacity of a Water Heater Measured in?

What is the Capacity of a Water Heater Measured in

Before we dive in too long, let’s settle a fundamental issue, which is the measurement used in describing water heater sizes. You should know that in the United States of America, the capacity of a water heater is measured in Gallons. On the other hand, standard water heater size is measured in Liters for other countries.

Size of Water Heater

Away from the question of what water heater size to choose, you must first be aware that there are various types of water heaters. These water heater variants all come in various sizes. Below, we’ll look at some of the popular sizes that these water heater types/variants come in.

Tankless Water Heater Sizes

Tankless Water Heater Sizes

Like the name infers, tankless water heaters do not have storage tanks. Also called flash, on-demand, inline continuous flow, instant-on or instantaneous water heaters, they boil water through the built-in heating coils as water flows through the appliance. They are compact-sized, energy-efficient and are a perfect fit for larger families whose members need to simultaneously access boiled water from several points. Best electric tankless water heater on the market come with more functionalities than other sub-types of tankless water heater sizes

Typically, tankless water heater manufacturers roll-out this variant of water heaters in various sizes and dimensions. But unlike traditional tank-based water heaters that are measured by gallon capacity, tankless water heater capacity is quantified by per minute flow rate i.e. gallon/liter per minute.

We found that most water heater brands produce tankless water heater sizes within the range of 3 to 8 GPM (gallons per minute).

Storage Tank Water Heater Sizes

Storage Tank Water Heater Sizes

Storage tank water heaters are by far the most popular variant of water heater appliances. They distinctly feature big, insulated tanks inside which they heat and store large volumes of water. There are two types: instant water heaters and storage water heaters.

Instant water heaters/geysers make hot water available at a moment’s notice. They hardly spend one to two minutes to heat the water before making boiled water available for use. To ease the possibility of making water available at the snap of a user’s finger, their storage capacity (i.e. storage tanks) are usually low, ranging between 5-6 liters/gallon at a given time.

On the other hand, storage water geysers have large storage tanks in which they heat and store larger volumes of water, for longer durations. They can process as much as 60liters/gallons of water at a given time, which accounts for why they aren’t as fast as instant water geysers.

Whether instant or storage geysers, storage tank water heaters can only heat a limited amount of water at any given time.

Electric Water Heater Sizes

Electric water heaters are credible alternatives to traditional gas water heaters. They run on electricity which powers the built-in heating elements in the appliance and is typically automatic in their operation. Though they are more efficient (in terms of capabilities) in heating water than gas water heaters, they significantly increase electricity bills. Because electricity-powered technologies are the new wave in today’s world, electric water heaters come in an endless range of sizes. It doesn’t matter what specification of electric water that you need, you’d always find a model that fits in.

Gas Water Heater Sizes

Gas water heaters are generally more cost and energy-efficient than their electricity-powered counterparts. They run on natural gas and usually boil water from the ground up because of the positioning of their heating element at the bottom of the unit. Typically, gas water heaters come in sizes that range from between 40-gallons to 100-gallons.

What size of water heater do I need?

We have established that water heaters are of various types, and each type comes in various sizes. Say you’ve arrived at your most preferred water heater type, the next question on your mind should be what size water heater should I get that would appropriately meet my needs? To do that, you must consider the following:

What size of water heater do I need
  • Available Space: Ensure that whatever size of water heater you finally go for, is one that can conveniently fit in the space allotted in your home
  • Household Size/Occupancy: Far more importantly, you should consider the number of the person(s) whose boiled water needs the water heater would constantly be meeting. Would the water heater be serving just yourself (and your partner) or what size water heater for family of 4?
  • Tasks: Here, you should give equal consideration to the number of simultaneous tasks that the heated water would be needed for. For instance, would you need water to run the shower, dishwasher, or washing machine simultaneously or separately?

Guide for Choosing Storage Tank Water Heater Size

Our research team did the calculations on your behalf, and arrived at this recommended water heater size for storage tank heaters:

  • 1-2 persons would need at least a 30-gallon capacity water heater
  • 2-3 persons would need at least a 40-gallon capacity water heater
  • 3-4 persons need at least a 50 gallon (electric) or 40 gallons (gas) capacity water heater
  • Larger households of 5 or more persons need at least an 80-gallon (electric) or 70 gallons (gas) capacity water heater

Guide for Choosing a Tankless Water Heater Size

You’ve been wondering what size tankless water heater do I need? Or how to size a tankless water heater needed for your household? Well, foremost, tankless water heaters do not have tanks with which you can measure the needed size in gallons or liters. Our team did the math and arrived at how to determine water heater size, such as the average heater GPM needed for simultaneous use of fixtures or appliances (e.g. shower, dishwasher, washing machine, etc.). Here’s how to choose a tankless water heater size:

  • 1-2 appliances need at least 3.5 GPM heater
  • 2-3 appliances need at least 5 GPM heater
  • 3-4 appliances need at least 7 GPM heater


We hope the guide put together by our research team at HandyHomeMaster has been more than in clarifying your doubts on and best water heater types. Hopefully, this would set you on the path of being able to make informed decisions regarding the capacity, size, or speed of the water heater to buy.

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