Division of Energy
Residential Energy Efficiency - Water Heating
Water heating is the third largest energy expense in the home, behind heating and air conditioning. Because a water heater is one of the large energy users, EnergyGuide labels are required. The labels are good guides for choosing the most efficient model you can afford.
The fuel you use to heat water is a big factor in water heating costs. If you have an electric water heater, the cost is probably two to three times as much.
When purchasing a new water heater, choose as small a tank as possible to meet your family's needs. In the upper right hand corner of the EnergyGuide label, you will find a listing of the First Hour Rating in gallons. This will tell you how many gallons of hot water that tank will produce in a single hour. Match that number to your needs.
Tank water heaters use either gas or electricity to heat water, then store 20 to 80 gallons in an insulated tank for use when a faucet is turned on. Heat is constantly lost through the tank walls (this is called standby heat loss which accounts for 20 percent to 60 percent of the total cost of heating water), and the gas burner has to reheat the same water even when no water is being used.
For tank-type water heaters, there are three main energy uses:
- Demand costs are the initial heating costs of water. The energy usage for demand will vary from summer to winter with the temperature of the incoming water. Lowering the tank temperature, and water usage efficiency, will lower demand costs. Using less hot water is the best savings measure.
- Standby losses amount to 20 percent to 60 percent of total water heating energy. Households using less hot water have higher percentage of standby losses. Lowering the tank temperature and adding extra tank insulation will cut standby losses. With an electric resistance tank, the use of an automatic timer can reduce energy used to reheat water.
- Distribution losses occur in pipes when hot water flows through them. Insulating pipes and short runs to plumbing fixtures will reduce distribution losses. Install a heat trap at the water heater to stop convection of hot water into the hot and cold water pipes above the water heater. Consider installing a small water heater, or an instantaneous heater, at the point of use to decrease your distribution losses substantially.
Instantaneous water heaters (also known as tankless water heaters) heat water as it is needed, using a gas burner or an electric element. The units can serve a single EAO or as centralized heaters to replace conventional tank water heaters. Although tankless water heaters will provide an endless source of hot water, most will provide the hot water at a slow flow rate (2 to 3 gallons per minute with a temperature rise of 90oF). Whether you should replace a conventional water heater with a tankless unit depends on the size and efficiency of the tank being replaced, the cost of energy used and the frequency and amount of hot water used. A tankless water heater is probably a good idea for a vacation home; or a household with small, and easily coordinated, hot water requirements; or a remote bathroom that could be served by a small point-of-use model. These heaters are more expensive to purchase.
Heat pump water heaters are more efficient than electric resistance units. A heat pump water heater uses a third to half as much electricity as a conventional electric resistance water heater. While the efficiency is higher, so is the purchase cost.
Batch solar water heaters are a do-it-yourself project that pays. These simple heaters preheat water using the sun's heat. They are inexpensive to build, and plans are available for their construction.
Hot Water Savings
- Fix any hot water leaks promptly.
- Install high-efficiency showerheads. The Energy Policy Act of 1992 mandates that any showerhead manufactured after January 1, 1994, must not be more than a 2.25 gallon-per-minute flow (at 80 psi). Some showerheads have valves that allow water shut-off at the shower head without losing temperature mix.
- Low-flow faucet aerators for the kitchen are covered in the same legislation. They reduce flow to 2.5 gpm.
- Take short showers.
- Use your dishwasher wisely instead of washing dishes by hand.
- Set washer cycles for the lowest temperature and water amount that will get clothes clean.
- Always rinse on cold water setting.
- Set water heater temperature at 120oF - 130oF.
- Add water pipe insulative wrap to the first six feet of the hot and cold water lines as they come off the water heater. However, be careful not to install the pipe wrap within 3 inches of any appliance exhaust flues.