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What Size Hot Water Tank Do I Need?

What Size Hot Water Heater Do I Need?

Your hot water heater is an important piece of equipment in your home. But like most people, you don’t know a lot about them and that can be stressful when it comes time to replace one. One of the decisions you will have to make is the size of hot water heater you need.

Regardless of the type of heater you decide on (tankless, storage tank, electric, or gas) you need to know three things:

  1. Household size – Number of people in your household.

  2. Peak water demand – This refers to how much hot water is used at the same time during the busiest time of the day. If four showers are taken every morning, you want to make sure your hot water supply is large enough so all of you have hot showers. Running out of hot water on a frigid Red Deer morning is not a pleasant experience.

  3. The size of the space you have to put your hot water heater.

Other factors to consider depends on the type of hot water heater you purchase.

Tankless Hot Water Heaters

These heaters don’t have a storage tank and give you hot water on demand. In addition to the above, you need to determine the following:

Flow rate need

Flow rate is the maximum amount of hot water a tankless hot water heater can provide at one time. For example, you will need a lower flow rate if your home only has one shower, or only one shower is used at a time. You will need a higher flow rate if you have three showers and all three of them will be used at the same time. 

Flow rates are measured in gallons per minute (GPM) or liters per minute (LPM). To determine the flow rate you require from your tankless heater, add the flow rates of all the fixtures and appliances you plan to use at the same time (showers, taps, washing machines, dishwashers, etc.).

Temperature Rise To determine the temperature rise you need to use this calculation: 

Desired Outgoing Water Temperature – Ingoing Water Temperature = Temperature Rise

  • Desired Outgoing Water Temperature is the hot water temperature you want.

  • Ingoing Water Temperature is the temperature of the water entering your water heater from your well or municipal water system.

    • Unless you know otherwise, use 10 degrees Celsius.

Storage Unit Hot Water Tanks

Also called a storage tank water heater. This is the most common type of hot water heater and probably the type you have right now. If you are buying this type, please make sure it is Energy Star rated. 

For this type of hot water heater, you need to think about:

First hour rating (FHR) 

This measures the amount of hot water the heater offers over one hour. This figure reflects the heater’s efficiency and gives you an idea of its hot water output during peak usage. For example, if your heater has a FHR of 90 gallons, it can provide 90 gallons of hot water in one hour. You want a FHR that is larger than the amount of hot water required by your peak water demand. 

Recovery rise rating 

This is another efficiency rating and it measures how much hot water your tank can supply in one hour after it has been completely drained.

Fuel source

The fuel source (gas or electric) of the water heater will impact the size of the tank you get.


Do you have a big soaking tub that you love to use? If yes, you want to make sure your hot water tank has the capacity to fill your tub, so you don’t end up with lukewarm baths.

It is essential to get the right size water heater for your needs. If you choose too small a water heater, you will run out of hot water and everyone will be cross with you. If you choose to large a water heater, you will have higher utility bills due to heat loss. Before your final decision, make sure you consult with a reputable professional and always hire a licensed plumber to install your hot water heater. Mistakes can be expensive and cause a lot of damage, so this is not the time for DIY.

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