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Water Heater Capacity Needs

water heaters

Water Heaters: A Guide to Sizing

The size of your water heater will affect both your utility bill and the comfort you experience in the shower or bath. If your water heater is too small, you will always be running out of hot water. If your water heater is too large, your utility bill will be unnecessarily high since you will constantly be heating and reheating a large amount of stored water. Therefore it is in your best interests to accurately determine the size of the water heater you will be needing.

Storage tank water heaters

If you have a traditional storage water heater, you need to ensure that the tank is large enough to meet your household’s peak demand. You can do this by looking at the water heater’s first hour rating or FHR and comparing this to your household’s desired FHR.

To calculate your household’s FHR you need to consider the amount of people in your home. A good rule of thumb is to use the number of bedrooms in your house plus one. You can then multiply this number by 12 gallons. This will give you the FHR. For instance, if you have a two bedroom apartment, you will multiply 3 by 12. This will give you 36 gallons. You can then either opt for a 30-gallon or a 40-gallon water heater, depending on factors such as whether there are two or three people living in the apartment, whether you prefer baths or showers, whether everyone living in the household takes a shower at the same general time of day, whether you live in a cold climate etc.

The general guidelines look something like this:

  • 1-2 people require a 30-gallon water heater
  • 2-3 people require a 40-gallon water heater
  • 3-4 people require a 40-50 gallon water heater
  • 5 or more people require a 50-80 gallon water heater

Tankless water heaters

If you have a tankless water heater, the capacity will be measured in flow rates as opposed to gallons stored. A tankless water heater’s flow rate should be able to meet your household’s peak demand. To determine this peak demand you will need to make a list of the water devices that are typically used at the same time. Then you will need to add up the flow rates of each such device. This will give you the flow rate of the water heater you require.

Solar water heating system

Determining the appropriate size of your solar water heating system requires you to determine the total collector area as well as the storage volume you’ll need to meet 90-100% of your household’s hot water needs during summer. The general guideline for the collector area is around 20 square feet for each of the first two household members. For each additional household member another 8 square feet should be added if you live in the US Sun Belt area, or 12 square feet if you live in the northern United States.

As regards the size of your storage tank, a 50-60 gallon tank is typically sufficient for one to two people while an 80 gallon tank should be large enough to meet the needs of three to four people.

We can help!

Should you have any questions or require any further information with regards to determining your water heater capacity needs, please feel free to contact us.