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What Size Water Heater Do I Need?

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Hot Water Heaters, Plumbing

How much hot water does your home need? Should you buy a water tank or a tankless heater—and how can you choose the right size? Don’t worry; Action Furnace is here to help. We’ll break down your different options and give you the information you need to make a choice that keeps your family comfortable.


Posted by Ryan | September 29, 2023

Hot water is essential for your household, but water heaters eventually need to be replaced. When the time comes, it’s vital to make sure you choose a new unit that will serve you and your family admirably for years to come.

Choosing the right size water heater is the best way to make sure your home stays energy efficient and enjoys an uninterrupted hot water supply. This comprehensive guide by our team at Action Furnace walks you through the steps involved in sizing and buying an appropriate new water heater for your home.

Types of Water Heaters

The size of your new water heater will depend on the kind of technology it uses. There are two main categories of water heaters: storage tanks and tankless systems. At Action Furnace, we sell both varieties—so here’s a quick explanation of how they differ:

Storage tank water heater in basement of home

Storage Tank Water Heaters

The most common water heaters in Alberta are storage tank heaters. These units hold a reserve of hot water, which is heated either by an electric element or a gas burner. The major downside? Once the stored water runs out, there’s a waiting period for the new water to heat up.


  • Less expensive up front
  • Higher flow rate (can send hot water to multiple fixtures simultaneously)
  • Maintenance needs are regular but relatively simple


  • Can temporarily run out of hot water if the tank’s contents are used up too quickly
  • Less energy efficient (more of a problem in older tanks)
  • Must constantly use energy to keep water in the tank hot
Whole home tankless hot water heater in basement of home being checked by technician

Tankless Water Heaters

Increasingly popular in Alberta, tankless water heaters (also known as on-demand heaters) heat water only when you need it. These units eliminate the need for a storage tank and the constant reheating of water, providing a more energy-efficient solution.


  • More energy efficient than hot water tanks
  • Can provide long-term energy savings that eventually offset their initial costs
  • More environmentally friendly


  • May have a limited flow rate
  • More expensive upfront
  • Maintenance is less frequent but can be more complicated than for storage tanks

How to Properly Size Your Water Heater

Sizing Storage Tank Water Heaters

A rule of thumb for sizing storage tank water heaters is as follows:

  • 2 to 3 people: 40-50 gallons
  • 3 to 4 people: 50-60 gallons
  • 5+ people: 75 gallons or more

Sizing Tankless Water Heaters

To estimate the size of the tankless water heater you’ll need, follow these steps:

  • Determine the number of hot water appliances you’ll be using simultaneously
  • Add up their flow rates to calculate the desired flow rate for your heater
  • Identify your desired temperature rise (typically around 39 degrees celsius higher than your ground water temperature) to ensure adequate performance

Still confused? Action Furnace’s expert team can assist in selecting the perfect unit for you.

Homeowner running hot water out of sink in home with adequately sized water heater

Benefits of Choosing the Right Size

Consistent Hot Water Supply

An improperly sized water heater will struggle to meet your home’s hot water needs. A correctly sized unit, on the other hand, ensures that everyone in your home has continuous access to hot water, without the need for a “shower schedule.”


An appropriately sized water heater runs more efficiently, saving you money on utility bills. Opting for a tankless unit could save you up to 30% on your natural gas bill compared to a traditional hot water heater.

Why Choose Action Furnace?

With cutting-edge installation techniques and an unwavering commitment to customer satisfaction, Action Furnace is the go-to choice for all your water heating needs. Join our Comfort Club for an annual tune-up, priority service, waived diagnostic fees, and a 20% discount on future repairs.

FAQ: Common Questions About Water Heater Sizing

How long does a typical water heater last?

The lifespan of a water heater varies depending on the type and maintenance. Storage tank water heaters typically last 10-15 years, while tankless units can last up to 20 years with proper care.

Can a water heater also improve water pressure?

A water heater primarily affects the temperature of the water, not its pressure. If you’re experiencing low water pressure, it may be due to other issues in your plumbing system. Contact our team to diagnose the problem and provide you with cost-effective solutions!

Why are tankless water heaters better for the environment?

Tankless water heaters are generally considered more eco-friendly because they only heat water when needed, reducing energy consumption. Some tankless units are also designed to reduce emissions.

How do I know if my water heater is the wrong size?

A water heater that’s too small may result in inadequate hot water supply, forcing you to limit usage or adopt a schedule. On the flip side, a unit that’s too large will consume more energy than necessary, increasing utility bills.

Can I install a new water heater by myself?

Do not attempt to install a new water heater by yourself. Without the proper qualifications and experience, you run the risk of damaging your home’s plumbing, voiding your new heater’s warranty, and potentially creating safety issues. Always contact our professionals to ensure that any new water heater you buy is installed correctly the first time.

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Written by Ryan Tutak

Ryan is considered one of Calgary's most knowledgeable residential HVAC specialists. Working in the industry for over 12 years, he's helped thousands of homeowners with their heating and cooling systems. Outside of running Calgary's most reputable HVAC business, you can find him on the Golf course practicing his short game or traveling with his family. His main goal is to create a positive collaborative culture, one in which his employees are excited to come in and are motivated to work hard. He spends the majority of his day working directly with Home Comfort Advisors, Service and Maintenance Technicians, and Customer Service Representatives ensuring they are fully prepared to lead the Home Service Industry in Customer Service.

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