Home Series Booklets

Increase your water heater's efficiency

Water Heater Blanket | Insulate | Turn Down the Knob |
Flush Sediment | More Information

In addition to cutting the demand for hot water, there are several things you can do to improve the efficiency of your existing water heating system. The upgrades will cost just a few dollars and take only a few minutes to complete—but will pay for themselves through reduced utility bills during the normal lifespan of a water heater.

Give your water heater a blanket
Wrapping an insulation blanket around the tank of your existing gas or electric water heater can save you money on water-heating bills. The blanket will reduce standby heat loss—heat lost through the wall of the tank—by 25 to 45 percent, and you’ll likely recover the cost of the blanket through reduced water-heating bills within a year.

Before you buy an insulation blanket, check the owner’s information that came with your water heater to make sure the manufacturer doesn’t prohibit installing one. The latest energy-efficient water heaters have very high insulation levels, which eliminates the need for adding an insulation blanket—and some manufacturers may void the appliance’s warranty if you do so.

When you go shopping for an insulation blanket, look for one with an insulation value of R-11 or higher. Buy a blanket kit designed for your type of water heater, and carefully follow the installation instructions. On an electric water heater, for example, you should avoid covering the unit’s thermostats. For a gas water heater, steer clear of the thermostat, the air inlet at the bottom and the flue on top of the unit.

Top

Insulate the hot water pipes
A great deal of energy and water is wasted—literally going down the drain—while you wait for hot water to reach the sink or shower. Insulating your hot water pipes will help reduce heat losses as the hot water flows to your faucet or showerhead, and it will help minimize standby losses when the tap is turned on more than once an hour. Your hot water system is a good candidate for pipe insulation if:

• You use water frequently throughout the day; e.g., everyone in your home takes a shower in the morning, one right after the other.
  
• The water pipe runs in your home are long.
  
• The pipes pass through an uninsulated crawl space or basement.

These types of water pipe insulation are available:

• Fiberglass batts come on a roll. You wrap the batt around the pipe, securing the batt in place with tape as you go.
  
• Foam or fiberglass tapes also come on a roll, and they’re self-adhesive so they’ll stick in place as you wrap the pipes.
  
• Foam or synthetic rubber tubes are split lengthwise, so all you do is slip them over the pipes and secure them. Some types are held in place with zip ties or tape, while others include self-adhesive strips along their cut lines. Rigid foam tubes usually have a higher insulation factor than the less-expensive flexible foam tubes, but the flexible ones are easier to trim and cut for corners or T-joints in pipe runs.

Measure the length and diameter of the water pipes you want to insulate before you head to the store. You may need a couple of sizes if you’re planning to insulate both the main hot water supply line (often 3/4-inch pipe) and the branch lines (1/2 inch) to individual fixtures and appliances. At the store, you’ll need to balance cost, convenience of installation and insulation factor; for example, even though fiberglass insulation may have a higher R-value than foam tubes, it costs more and will take longer to install—and its payback period will be longer.

Before you begin installation, vacuum the dust and debris off the pipes. Wear safety glasses to keep any remaining debris that gets knocked loose from falling in your eyes; for fiberglass insulations, wear gloves and a dust mask too. Insulate the first six feet of both the hot and cold water pipes, starting where the pipes go into the water heater. Also insulate the hot water pipe runs that go to frequently used fixtures or appliances.

Turn down the knob and save
A temperature of 120 degrees should meet the hot water needs of most households. This is well below the 140-150 degrees found in many homes, which—in addition to wasting energy—can be a scalding hazard, especially to children and seniors.

Each 10-degree drop in water temperature can save three to five percent on water heating costs. Most people find the 120-degree temperature to be satisfactory, especially considering that a “hot” shower usually runs around 105 degrees. However, if you have an older dishwasher that does not have a water-heating booster, a 140-degree temperature may be necessary for the appliance to effectively clean dishes, kitchen utensils and pans.

Determine the hot water temperature by running hot water into a bowl for at least a minute and checking the temperature with a candy thermometer. If the temperature is higher or lower than 120 degrees, adjust the thermostat on your water heater a little bit (following the manufacturer’s instructions), wait an hour and recheck the temperature.

Top

Flush sediment from the tank twice a year
Sooner or later, rust and scale will build up inside the water heater’s tank, making it work less efficiently. As the water heater cycles through hot and cold periods, it expands and contracts, causing rust and scale to drop to the bottom of the tank.

To remove the sediment, follow these steps:

• Following the water heater manufacturer’s directions, shut down a gas-fired water heater or turn off the power to an electric unit, and allow the tank to cool.
  
• Close the cold-water supply valve, or shut off the water at the meter.
  
• Open a hot water tap in the house.
  
• Open the drain valve at the bottom of the tank and let the water flow until it’s clear; catch the water in a bucket or attach a short section of garden hose and run it to the nearest drain.
  
• Close the drain valve, and open the cold-water supply valve. Don’t close the hot water tap until all air is exhausted from the tank and water flows
  from the tap.
  
• Following the manufacturer’s directions, relight the pilot light on a gas-fired water heater or turn on the power to an electric unit.

The U.S. Department of Energy’s Web site includes information on different types of water heaters. Go to US DOE Energy Efficiency and Renewable Energy website, http://eere.energy.gov/consumer/.

Get more information
The material in this article was adapted from a new book, Home Heating and Cooling, just released by the Iowa Energy Center. Besides offering much more detail on the topics discussed here, this book also covers making the most of your air-conditioning system, discusses landscaping your yard for year-round comfort and lists many sources of additional information on energy-saving topics.

The first book in the series, Home Tightening, Insulation and Ventilation, was released last summer and is still available. To get your free copy of one or both of these books:

• Call your utility company to see if you can stop by the office and
  pick up a copy;
  
• Download a PDF copy at the Iowa Energy Center Web site: www.energy.iastate.edu/homeseries/;
  
• Request a copy by e-mailing the Iowa Energy Center at
  iec@energy.iastate.edu; or
  
• Call the Iowa Energy Center at 515-294-8819 to ask for a copy by mail.

Contact:
Amy Swenson, Iowa Energy Center, (515) 294-4391, swenson@energy.iastate.edu

Top