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Should you buy a gas or electric water heater?

Electric Heater Costs | Gas Heater Operating Costs | More Infomation

By a wide margin, storage tank water heaters are the most common type used in homes, and they typically range in capacity from 40 to 60 gallons. They’re powered by electricity, natural gas or liquid propane. Electric units generally require 240-volt electrical service, while gas units require a gas line (and a tank for propane).

All storage tank water heaters operate in pretty much the same manner. The tank is surrounded by a blanket of insulation and is enclosed in a metal or polymer (plastic) jacket. Cold water from the water service flows through an inlet at the top of the tank and goes down an internal supply pipe to the bottom of the tank. A pair of heating elements (electric) or a burner (gas) heat the water in the tank. When a tap is opened, hot water exits through an outlet on top of the tank; at the same time, cold water flows into the bottom to replace the outgoing heated water. A thermostat keeps the water at the requested temperature.

Three other components have special functions. A pressure relief valve located on top of the tank (or on the side, near the top) prevents excess pressure buildup in the tank caused by overheating; the valve opens to release the pressure if water inside overheats to a dangerous level. An anode hanging in the water in the tank helps prevent tank corrosion. And a drain valve near the bottom of the tank lets you regularly drain a few gallons of water from the tank to remove rust and sediment buildup.

Up-front costs are lower for an electric water heater
An electric water heater is less expensive to purchase than a gas-fired model, and it’s easier to install and maintain. It will convert electric power to heat at very high efficiency, so its Energy Factor will be superior to that of comparably sized gas water heaters. An electric unit also is easy to turn off and on, and there’s no need to worry about gas fumes, combustion exhaust pollution or lighting a pilot. On the other hand, when energy costs are added to the equation an electric water heater likely will be more expensive to operate than a gas unit—even if your local utility offers off-peak rates or load-control programs.

There are two special categories of electric water heater to consider too; both take a unique approach to saving energy. One type features “smart” controls with multiple modes you can set, including one that tells the computer inside to automatically adjust the water temperature to match your family’s hot water usage; this reduces standby losses when no hot water is needed. The other kind has a lifetime warranty and includes a domed polyethylene outer shell and a seamless molded plastic tank inside; the wide spacing between them is filled with foam insulation—even at the top, where it’s needed most.

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Operating costs are lower for a gas water heater
A gas water heater is more expensive to buy than an electric one, and a qualified service person will need to install it. Besides the basic unit, installation includes extra components for the gas line and the venting system.

A gas water heater generally is less efficient than an electric one, with an Energy Factor for the most-efficient gas models running about .62. A gas unit can lose up to a quarter of its heating energy during the combustion process while heating the water; much of the waste heat just goes up the flue and out the chimney. On the other hand, at today’s natural gas prices a gas water heater should be less expensive to operate (compared to electricity). Liquid propane usually is more expensive than natural gas.

For all types of gas water heaters, appropriate venting is essential for proper operation and your family’s safety. The standard vent that comes with most basic gas water heaters is a simple unit that directs combustion byproducts through a flue that passes through the middle of the tank, up the chimney and out of your home. However, if you live in a very airtight house, the flue is extremely long or the water heater is located in a conditioned space, choose a water heater with a power vent that uses a fan to carry the exhaust outside; you may need to add an outside air intake for improved combustion too. Finally, a direct vent that combines the exhaust flue and an outside-air intake into a single unit might be a good choice if locating the water heater along an outside wall makes sense in your home. Since a direct vent relies on natural air currents—there’s no fan—the vent only can extend about four feet from the water heater to the outside of the house.

Keep these things in mind when you go shopping Look for these features in both electric and gas storage tank water heaters:

• A magnesium anode rod that will last longer than a mild-steel anode rod.
  
• The highest rating of CFC-free tank insulation.
  
• A specially coated ceramic- or porcelain-lined tank that resists corrosion more effectively than a standard glass-coated tank.
  
• A sediment-reduction system—such as a dip tube that creates turbulence in the tank— to reduce lime and sediment buildup.
  
• The longest standard manufacturer’s warranty that’s available. (Sometimes the tank has different warranty than the water heater’s other components.)
  
• Heat traps to prevent heat loss caused by siphoning of heated water into pipes.
  
• A brass (not plastic) drain valve.
  
• In addition, for an electric water heater look for long-lasting heating elements made from special materials other than standard copper.

If you’re comparing only gas water heaters, look for these items too:

• A super-efficient, sealed combustion chamber with a burner that reduces nitrous oxide (NOx) emissions.
  
• Compliance with flammable vapor ignition resistant (FVIR) standards that prevent unintended ignition of flammable vapors from products such as solvents, cleaning products, gasoline, aerosol sprays and adhesives.
  
• A viewing window to check burner function.
  
• A piezoelectric (pushbutton) or electronic pilot light igniter.

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/.

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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

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