High Efficiency Electric Water Heating
Purchasing a high-efficiency electric water heater or insulating your hot water tank is an easy way to save energy dollars. Most domestic hot water systems are "stand-by systems" - that is, water is kept hot and stored for use whenever it is needed. A hot water tank that is not properly insulated loses more heat through the top and sides.
High-efficiency electric water heaters usually have high levels of foam insulation, often as high as R-19, between the tank itself and the exterior of the water heater. An electric water heater without internal foam insulation can be made more efficient by adding an insulation "blanket" or "jacket." These blankets are relatively inexpensive and can be installed by a contractor or the homeowner. Insulating the tank reduces the loss of heat to the surrounding air.
Electric resistance heating elements in the tank (standard electric water heating) transfer virtually 100% of their energy to the surrounding water as heat. Higher-efficiency heat pump water heaters are available which operate at an efficiency of over 100%, and often over 200%. They transfer heat from the surrounding air, ground, or well water to the water in the tank.
What to Look For
Look for a well-insulated water heater. The better the R-value of insulationon the tank, the more energy-efficient it will be. The size of the heating elements (whether 3 kW or 4.5 kW) has no bearing on efficiency, only on the time it takes to reach the temperature set on the thermostat after hot water has been drawn off.
Insulating the Tank
High-efficiency models come from the manufacturer with built-in foam insulation. This type of water heater does not need to be wrapped with additional insulation. There is often a label cautioning homeowners against doing this. For models with less internal insulation, the efficiency can be increased by installing external tank insulation.
If your hot water tank is insulated to R-10 or less, consider installing an insulation jacket or blanket, particularly if it is located in an unheated area such as an unfinished basement or garage. Although the surface of the water heater may not feel warm, the tank may still be losing heat. To illustrate this, hold your hand against the side of the tank, then hold your hand against a metal object or surface in the same room, perhaps a metal shelf or tool box. Usually the other metal will feel cooler than the water heater tank. The difference in temperature is due to heat loss from the tank.
Installation Recommendations
Vinyl-faced fiberglass insulation should always be installed with the vinyl facing on the outside. Secure the sections of insulation using high temperature duct tape. Do not install the insulation over the water heater operating instructions or the other components identified below.
For an electric resistance water heater, install insulation on the sides and top. Cut the insulation to leave holes for the pressure relief valve and plumbing pipes. Remember to cut the jacket for access plates.
Water Heater Timer
A "standby system" keeps water hot at all times; however many consumers only use hot water during relatively short periods of time each day. To further reduce the energy dollars spent on hot water, consider the installation of a water heater timer. The timer will turn the water heater on for high-use periods and off during low-use periods. Most timers will allow multiple on/off periods per day and have a manual override switch to allow water heating at any time.
Operation and Maintenance
- The recommended temperature for an electric water heater is 60° C (140° F). Any hotter, you risk the danger of scalding. Bacteria can grow at a lower temperature.
- Follow the manufacturer's recommendations for flushing the tank.
- Check the insulation wrap, if externally insulated, to be sure it remains snug.
- Do not place sharp or hot objects near the tank which might puncture or damage the insulation and/or tank wall.
A properly installed hot water tank, with either built-in foam insulation or an external insulation jacket, can reduce your energy bills without sacrificing comfort or convenience.
