Replacement Electric Water Heater

When the time comes to replace your electric water heater, a new high-efficiency model can be a worthwhile investment in energy savings. Next to heating or cooling, water heating is often the largest energy expense in the home.

Most residential electric water heaters heat the water with electric heating elements and store it in an insulated tank until needed. They use energy both to heat the water and to keep it hot until it's used. The electric heating elements are immersed in the water inside the tank and heat the water with 100% efficiency. Since there is no way to improve the efficiency of an electric heating element, improvements to electric water heaters have focused on reducing stand by losses, the heat lost from the water being stored in the tank.

Water Heater Efficiency Ratings

The standard efficiency rating for water heaters is called an Energy Factor (EF), which is a decimal equivalent of a percent efficiency (.89 EF = 89% efficient). It compares the heat energy delivered to the water to the total energy consumption of the water heater. New electric water heaters have Energy Factors ranging from .86 to as high as .95. The higher the Energy Factor, the less it will cost to heat water.

First Hour Rating

This is the amount of hot water that the water heater can supply in the first hour of operation. It is a combined measurement of how much water is stored in the water heater and how quickly the water heater can heat cold water to the desired temperature. You can use this rating to select the appropriate size water heater and to compare hot water delivery capabilities of similar models.

Efficiency Improvements

New electric water heaters incorporate higher levels of insulation between the tank and the outer shell or jacket to slow down heat losses to the surrounding air and keep more of the heat in the water. High-efficiency electric water heaters can have insulation values as high as R-19. With less heat loss, the heating elements don't need to run as often or as long to maintain the desired temperature. The fewer hours the elements are on, the less it costs to operate the water heater. In the past, water heater insulation blankets were widely recommended - with newer water heaters this additional insulation is unnecessary.

Heat can also be lost when hot water in the tank expands and flows a short way back up the cold inlet pipe. Newer electric water heaters incorporate a heat trap to prevent this, keeping the heat in the tank.

Heat Pump Water Heaters and Heat Recovery Systems

Electric heating elements that convert electricity to heat can never be more than 100% efficient. Heat pump water heaters use a refrigerant cycle (the same process used by heat pumps for space heating) to extract heat from the surrounding air and transfer it to the water in the tank. By recapturing existing heat rather than creating new heat, they can achieve efficiencies of 200% or even higher. For more information, see "Heat Pump Water Heaters".

A heat recovery or heat reclaim water heater connects to a central air conditioner and reclaims some of the heat that would be rejected outdoors. These units have been popular for some time in climates with high air conditioning usage, as they can provide low-cost hot water whenever the air conditioner is running. Unfortunately, most major air conditioning manufacturers now discourage their use with new air conditioners.

Water Heater Timers

Most households only use hot water for relatively short periods of time each day. Water heater timers restrict the hours that the heating elements run, reducing the stand-by losses from the tank. Because newer water heaters are better insulated, standby losses are reduced, so the savings from using a timer are minimal, except when combined with a "time of use" electric rate. Some utilities offer these rates, where the cost is higher during "peak" hours (times of highest demand) and lower during "off peak" hours. If the timer is set so that the heating elements only operate during off peak hours, the savings can be significant (actual savings will depend on the difference between standard and off peak rates).

What to Look For

The Federal Trade Commission requires all residential water heaters be labeled with an "EnergyGuide" label. This label shows the estimated annual operating cost for that particular water heater and how the cost compares with other comparable models.

The Air Conditioning, Heating and Refrigeration Institute (AHRI) sponsors an efficiency certification program that verifies manufacturers' equipment efficiency ratings according to a standard test method. AHRI maintains an online directory that lists the manufacturer, model number and Energy Factor of all tested water heaters.

Related Topics: