Q Is it true that a 50-gallon water heater would be more efficient than a 40-gallon unit because it would cycle on fewer times during the day?
A No. The federal standard for minimum efficiency actually is lower for a 50-gallon water heater than for a 40-gallon unit, said Phil Smith, energy specialist at the Minnesota Office of Energy Security.
It's not the storage capacity of a water heater that determines its efficiency, he said. Rather, there are two measures of performance: energy factor and first hour rating.
Energy factor (EF) is a measure of the overall efficiency of the water heater. It takes into account the heat loss of the shell, plumbing connections, central vent losses and additional variables.
The first hour rating is a measure of the water heater's ability to provide hot water. It is the amount of hot water the unit can supply in the first hour of operation. It is a combination of how much water is stored and how quickly the heater can heat water to the desired temperature. This is the measure to use in sizing the water heater to meet your needs.
The capacity of a water heater is an important consideration, but the first hour rating is far more important, according to Smith. A water heater should provide enough hot water for your household at the busiest time of the day. Use the first hour rating as your benchmark for meeting the volume of hot water you need.
That rating is included in product literature and on the EnergyGuide label alongside the efficiency rating on your water heater.
To determine your family's first hour rating, you can use the simple calculator found in the publication "Water Heaters," from the Minnesota Office of Energy Security. Go to www.energy.mn.gov and click on Home Energy Guides. Or call 651-296-5175 for a copy (outside the Twin Cities calling area, call 1-800-657-3710).
