Water Heater
Federal appliance standards require that all water heaters achieve a certain rating on a standardized scale. The rating for water heaters is called the Efficiency Factor (EF), based on the use of 64 gallons per day under standard test conditions. The federal appliance standards require the following EFs for electric water heaters:
Size……………………… Efficiency Factor (EF)
30 gallon……. …………………… 0.91
40 gallon………………………….. 0.90
50 gallon………………………….. 0.88
60 gallon………………………….. 0.87
The most efficient electric water heaters have EFs around 0.94 to 0.96.
This Energy Factor can be converted into an estimate of annual consumption, for standard operating conditions. This estimate, in kWh/yr is the number you will see on the yellow Energy Guide sticker. Here are some general trends in water heater efficiency:
1. Larger tanks tend to be less efficient than smaller tanks, because they have more surface area through which to lose heat.
2. Electric water heaters are more efficient than gas or propane heaters because the latter lose heat from the exhaust gases in the burner. As a result, some of the heat produced just goes up the chimney. However, because electricity tends to cost more than gas, water heating bills are usually higher with electric than gas.
3. Heat pump water heaters are more efficient than electric resistance water heaters because they don’t generate the heat used to heat the water; they just move heat from one place to another. Heat pump water heaters cost more to purchase than other types of water heaters.
What is the average setting on an electric hot water heater?
Typically, water heaters have three temperature settings: high, medium and low. These settings correspond roughly, depending on the age and condition of the water heater, to about 160°F for high, 140°F for medium, and 120°F for low. Most people have the temperature set to medium, or around 140°F. If it is not already there, you should consider lowering the thermostat to 120°F, which will save you about 3 to 5% in water heating costs for each 10°F reduction. You might want to consider a timer for your water heater that turns it off when not in use, say between 10 or 11 pm to 6 am. This would also lower your water heating costs by cutting down the amount of energy lost through the walls of the tank during the night.
If you turn your hot water heater off during the day, won’t it cost more because you then have to heat up the whole tank and wait minutes before taking a shower? Also, isn’t it kind of an inconvenience?
No, water heater energy consumption increases with higher water temperatures, and water heaters use more energy to heat water up and keep it hot than they do to heat it up once, because heat is lost through the walls of the tank in proportion to the tank temperature. The same energy is required to heat up the water regardless of whether it is heating a little bit at a time, or all at once. Heat losses through the tank walls or pipes simply add to the cost. So, turning the water heater off for a few hours each day actually saves some energy. This strategy works best for electric water heaters, because they lose heat less rapidly than gas or oil water heaters.
If you turned your hot water heater off during the day, it would be an inconvenience if you use more hot water than is stored in the tank. Installing a timer that turns the water heater off or that lowers the temperature during the night generally poses no inconvenience at all. These timers can be set to turn the heater back on an hour or so before you get up in the morning, so your hot shower is ready to go when you are.
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