Determining Energy Efficiency of Storage, Demand, and Heat Pump Water Heaters
Use the energy factor to determine the energy efficiency of a storage, demand (tankless or instantaneous), or heat pump water heater.
The energy factor (EF) indicates a water heater's overall energy efficiency based on the amount of hot water produced per unit of fuel consumed over a typical day. This includes the following:
- Recovery efficiency – how efficiently the heat from the energy source is transferred to the water
- Standby losses – the percentage of heat loss per hour from the stored water compared to the heat content of the water (water heaters with storage tanks)
- Cycling losses – the loss of heat as the water circulates through a water heater tank, and/or inlet and outlet pipes.
The higher the energy factor, the more efficient the water heater. However, higher energy factor values don't always mean lower annual operating costs, especially when you compare fuel sources.
Product literature from a manufacturer usually provides a water heater model's energy factor. Also, see the Product Information resources listed on the right side of this page (or below if you've printed it out).
Don't choose a water heater model based solely on its energy factor. When selecting a water heater, it's also important to consider the following:
Related Information
- Determining Solar Water Heater Energy Efficiency
- Energy-Efficient Water Heating
- Tankless Coil and Indirect Water Heaters (includes information on determining energy efficiency)