7.9 Energy Efficiency
7.9 Energy EfficiencyThe federal efficiency standards for water heaters took effect in 1990, assuring consumers that all new water heaters meet certain minimum-efficiency levels. The latest standards went into effect in 2010, and even more strict standards will go into effect in 2029.
Water heater efficiency is reported in terms of the universal energy factor (UEF). UEF is an efficiency ratio of the energy supplied in heated water divided by the energy input to the water heater, and it is based on recovery efficiency, standby losses, and cycling losses. The higher the UEF, the more efficient the water heater.
- Electric resistance water heaters have EFs ranging from 0.93 and 0.95. T
- Gas water heaters from 0.63 and 0.8 with some high-efficiency models ranging around 0.93. To meet Energy Star requirements must be greater than 0.81.
- Tankless gas water heaters 0.82-0.97. To meet Energy Star requirements must be greater than 0.95.
- Heat-pump water heaters from 3.3-4.1. To meet Energy Star requirements must be greater than 3.30.
- Solar Hot water heaters To meet Energy Star requirements must be greater than 3.00 with electric back up, and greater than 1.80 with gas back up.
DOE replaced Energy Factor (EF), the previous measure, in 2017 with the adoption of revised testing procedures and metrics to help consumers and contractors easily and precisely compare the efficiency among water heaters for a given installation scenario. UEF provides a consistent standard, simplifies the selection process, and more accurately measures energy usage under real-world conditions compared to previous measurement models. For more information, check out Energy Star's website on "What is Uniform Energy Factor and Why Does it Matter?"
Other Considerations
In addition to UEF, also look for a water heater with at least one-and-a-half inches of tank insulation and a heat trap. If your (tank) hot water heater is older, you can increase the efficiency by adding a hot water heater blanket. The can increase the R-value (insulation) of the hot water heater by trapping the heat inside. They can be purchased at any home improvement store for about $20-$40.
In addition, capacity of a water heater is an important consideration. The water heater should provide enough hot water at the busiest time of the day. For example, a household of two adults may never use more than 30 gallons of hot water in an hour, but a family of six may use as much as 70 gallons in an hour.
The ability of a water heater to meet peak demands for hot water is indicated by its "first hour rating." This rating accounts for the effects of tank size and the speed by which cold water is heated. Water heaters must be sized properly. Over-sized water heaters not only cost more but increase energy use due to excessive cycling and higher standby losses.