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    Question ID:   5916         Current Version: 1
Question: How do I determining energy efficiency of storage, demand, and heat pump water heaters?
Category: Home Maintenance & Repairs > Heating & Cooling
Keywords: determine, energy, efficiency, storage, demand, heat, pump, water, heater, heat, system, EF, factor
Type: how
Rating:(0 ratings)    Views: 497    Discussions: 0   In Watch Lists: 1  

 
    Answer:
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.

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:

  • Size
  • Fuel type
  • Overall cost
  • First hour rating.
Source: Energy Efficiency and Renewable Energy, U.S. Department of Energy
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