Water Heater Sizing & Type

Water Heater Sizing is determined by the number of bathrooms and number of members of the household, along with the source of heat and capacity.  A Professional Plumber is able to make this calculation to determine the best size storage tank water heater for a home.

To properly size a storage tank water heater for your home use the water heater’s first hour rating. The first hour rating is the number of gallons of hot water the heater can supply per hour (starting with a tank full of hot water). It depends on the tank capacity, source of heat (burner or element), and the size of the burner or element.

The EnergyGuide label lists the first hour rating as “Capacity (first hour rating).” The Federal Trade Commission requires an EnergyGuide label on all new conventional storage water heaters. Product literature from the water heater manufacturer may also provide the first hour rating. Look for water heater models with a first hour rating that matches within 1 or 2 gallons of your peak hour demand — the daily peak 1-hour hot water demand for your home.

To estimate your peak hour demand:

  • Determine what time of day (morning, noon, evening) your family uses the most hot water in your home. Keep in mind the number of people living in your home.
  • Estimate your maximum usage of hot water during this one hour of the day—this is your peak hour demand.


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