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Information about energy-efficient electric waterheaters in this section includes the following:
Also provided is a portable document format version of How to Buy an Energy-Efficient Electric Water Heater (PDF 205 KB, 2 pp). Download Acrobat Reader.
| Efficiency Recommendation |
| Storage-Type (Rated Volume) |
Recommended |
Best Available |
| Energy Factora |
Annual Energy Useb (kWh/year) |
Energy Factor |
Annual Energy Use (kWh/year) |
| Less than 60 gallons |
0.93 |
4,721 |
0.95 |
4,622 |
| 60 gallons or more |
0.91 |
4,825 |
0.92 |
4,773 |
a Energy Factor is an efficiency ratio of the energy supplied in heated water divided by the energy input to the water heater.
b Based on DOE test procedure, see 10 CFR 430, Sub-Part B, Appendix E.
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| Cost-Effectiveness Example |
| Performance |
Base Model |
Recommended Level |
Best Available |
| Energy Factor |
0.90 |
0.93 |
0.95 |
| Annual Energy Use |
4,879 |
4,721 |
4,622 |
| Annual Energy Cost |
$293 |
$283 |
$277 |
| Lifetime Energy Costa |
$2,962 |
$2,862 |
$2,795 |
| Lifetime Energy Cost Savings |
— |
$100 |
$167 |
a Lifetime Energy Cost is the sum of the discounted value of annual energy costs based on average usage and an assumed water heater life of 13 years. Future electricity price trends and a discount rate of 3.0% are based on federal guidelines (effective from April, 2004 to March, 2005).
Cost-Effectiveness Assumptions: The Base Model is a 50 gallon storage-type water heater with an EF of 0.90, which just meets current US appliance standards and a FHR of 62 gallons. The Recommended Model is a 50 gallon storage-type with and EF of 0.93 and a FHR of 60 gallons. The Best Available is a 50-gallon storage-type with an EF of 0.95 and a FHR or 58 gallons. Annual energy use calculation is based on the standard DOE test procedure. Electric water heater model: 50 gallon tank, 58 to 62 gallon first hour rating (FHR). Usage assumption: temperature setpoint of 135°F, inlet water temperature of 58°F, daily hot water demand of 64 gallons, and 365 days per year of use. Assumed electricity price: $0.06/kWh, the federal average electricity price in the U.S.
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FEMP provides a cost calculator to compare the energy costs for your selection with FEMP-recommended and "best available" gas water heater models. You can model different scenarios by varying gas cost, hot water usage, and efficiency (energy factor).
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The federal supply sources for electric water heaters are the General Services Administration (GSA) and the Defense Logistics Agency (DLA). GSA sells water heaters through its Multiple Awards Schedule program and on-line shopping network, GSA Advantage! DLA sells them through the Defense Supply Center Philadelphia and on-line through DoD EMall. Whether purchasing water heaters from GSA, DLA, or a commercial source check the yellow EnergyGuide label to find models that meet the recommended Annual Energy Use (kWh/year). In solicitations and contracts, specify an Energy Factor (EF) that meets this efficiency recommendation.
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Storage-type water heaters are the most commonly used products but also have significant standby losses. Where hot water use is low (i.e. rest rooms in office buildings) installing a demand-type (instantaneous) electric water heater can result in substantial savings. These products heat water as it is used and, due to their compact size, are typically located near the point of use. Absence of a storage tank and shorter distribution lines greatly reduces standby losses and increases efficiency.
Where natural gas is available on-site, a gas water heater will almost always be more cost-effective than an electric model. Depending on the climate and energy costs, a solar-assisted or heat pump water heater may result in substantial energy and cost savings.
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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. ACEEE's Consumer Guide and GAMA Consumer Directory (see "For More Information") provide guidance on proper sizing. A water heater should be selected based on first-hour rating (FHR), not tank size. When installing storage-type water heaters, select the smallest models that meet the FHR and this recommendation.
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Energy costs increase with water temperature. Dishwashers require the hottest water of all household uses, typically 135° to 140°F. However, these devices are usually equipped with booster heaters to increase the incoming water temperature by 15° to 20°F. Setting the water heater between 120° and 125°F and turning the dishwasher's booster on should provide sufficient hot water while reducing the chances for scalding. Turning electric water heaters down or off during unoccupied periods will save significantly on energy costs, as will water heater timers or load controls in building with time-of-use rates or demand charges.
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