Water Heating

The water heater is the second-largest energy user in the home after your heating and cooling system. In an average home, water heating accounts for about 25% of your total energy usage.

How Water Heaters Work

Storage water heaters, ranging in size from 20 to 80 gallons, are the most commonly used water heaters in homes today.

When you turn on the hot water faucet, hot water is pulled out of the top of the water heater and cold water flows into the bottom to replace it. The water in the tank is heated by an electric resistance heating element, gas, or oil.

The most important energy-related feature of storage water heaters is the amount of tank insulation. The more energy-efficient models on the market today have an R-value of at least 20. (The higher the R-value the better the insulator.)

Demand or instantaneous water heaters have no storage capacity. The water is heated as needed, but the flow rate is limited. If you have a couple of teenagers in the house, or you need to do a load of laundry while someone is in the shower, then a demand water heater may not provide an adequate supply of hot water.

How Heat Pump (Hybrid) Water Heaters Work

Heat pump water heaters use electricity to move heat from one place to another instead of generating heat directly. Therefore, they can be two to three times more energy efficient than conventional electric resistance water heaters. To move the heat, heat pumps work like a refrigerator in reverse.

While a refrigerator pulls heat from inside a box and dumps it into the surrounding room, a stand-alone air-source heat pump water heater pulls heat from the surrounding air and dumps it – at a higher temperature – into a tank to heat water.

Visit Energy.gov’s page on heat pump water heaters to learn more.

Ways to Reduce Your Water Heating Costs

The number of people in your household, the amount of laundry you do, and your dishwashing habits have an impact on your hot water usage.

  1. Lower the water heater temperature – Water heated to between 120° and 125° F is hot enough for most households; this is about midway between the “low” and “medium” settings on most water heaters – If you do not have a dishwasher or have one without a booster heater, keep the water temperature at the medium setting
  2. Conserve water – Water-conserving or low-flow shower heads can cut hot water use in half – Limiting showers to five minutes could also reduce hot water use
  3. Insulate your water heater – An insulating jacket may pay for itself through energy savings in less than a year; the older the water heater, the greater the potential savings – Always follow the manufacturer’s instructions given in your owner’s manual. (Water heater jackets are not recommended for all models.)
  4. Install a timer – A simple timer that shuts the water heater off 12 hours a day will pay for itself in less than a year – Savings are greater for water heaters located in unheated garages and basements

Additional Resources