Water heater tank size matters when it comes to heating faster & using less energy

When choosing the right size tank for your water heater – bigger isn’t always better. Matching your water heater capacity to the hot water needs of your family can save you money and make your water heat faster.

While you can choose between a storage tank, tankless water heater, or solar tank – this post will focus on storage tanks as they are found in most households.

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Understanding First Hour Rating

The first hour rating is how much hot water your heater can deliver in a single hour. It depends on tank capacity, fuel source, and size of the fuel source.

Tank Capacity x .70 + Recovery = First Hour Rating.

On the Energy Guide label, the first hour rating will be in the top left corner of the label.

Match first hour rating within 1-2 gallons of your peak hour demand.

Peak hour demand is how much hot water your family will use in one hour.

Use this chart to determine peak hour demand:

Use Average Gallons of Hot Water Usage Times per hour Gallons used in One Hour
Shower/Bath 20 x =
Shaving 2 x =
Hand/Face Washing 2 x =
Hand dishwashing 2 x =
Food Preparation 2 x =
Automatic dishwasher 6 x =
Clothes washer 7 x =
Total 20 x =

Adapted from energy.gov

Higher Energy Factor rating = more efficient tank

The energy factor indicates the efficiency of many home appliances, including water heaters, dishwashers, clothes washers, and clothes dryers. A higher energy factor on your hot water heater means:

  • More efficient recovery time(how efficiently heat is transferred to water)
  • Lower standby losses (heat loss per hour from stored water)
  • Fewer cycling losses (the loss of heat as hot water circulates through tank)

Energy Star rated propane gas water tanks should have an Energy Factor greater than 0.67 for 55 gallon or less tanks, and an Energy Factor greater than 0.77 for 55 gallon or more tanks.

Additional factors that influence size of your water heater

Your family may be classified as higher demand if you have more bathrooms, hot water appliances, or similar shower schedules in your home.

  • Household bathroom count
  • Schedules of people in the home
  • Other Hot Water Appliances

Common gallon capacity required per family-size

Family Size Demand Gallon Capacity Required (for Gas)
5 + High 75-100
Low 50
3-4 High 50-75
Low 40
2-3 High 40-50
Low 40
1-2 High 40-50
Low 30