Saturday, April 25, 2009

Water Heaters


Hot showers without guilt

Heating water in our homes accounts for 17% of all home energy use in the United States. The first step in shrinking your water heating energy is to conserve. The less hot water you use, the less you'll pay for energy and the smaller your carbon footprint will be. To do this, you don't need to endure cold showers--you just need to use your hot water wisely. And when it's time to replace your existing water heater, step up to a high-efficiency model. You'll be amply rewarded in savings of energy and money. [youtube][/youtube] Watch Sierra Club's Owen Bailey teach you how to wrap your hot water tank to save money!

Top Tips

At home

  • Take it easy. Don't run the hot water tap longer than necessary and don't use hot water for tasks that are accomplished just as well with cold water, such as washing clothes.

  • Fix leaky pipes and faucets.

  • Install low-flow faucets and showerheads.

  • Buy efficient appliances. When replacing clothes washers and dishwashers, choose water-efficient models--the less water these appliances use, the less water heating energy you need.

  • Turn down the heat. Lower your water heater's thermostat to 120°F (about the midpoint between the low and medium settings, if degrees aren't marked on the thermostat). That's plenty hot enough for all household uses, unless you have an old dishwasher that doesn't have an internal booster heater. And when you're going out of town for more than a few days, turn the water heater's thermostat to the lowest setting.

  • Blanket your tank. Cut energy use by wrapping the water heater tank with an insulating blanket. Blankets, or jackets, as they're sometimes called, can reduce the operating costs of older models by 4% to 9%. Here's a rule of thumb: if the outside wall of the water heater feels warm to the touch, it needs a blanket. They're inexpensive, available at most home improvement stores, and easy to install if you follow the directions that come with the blanket.

  • Insulate all accessible hot water pipes. This reduces heat loss and provides faster delivery of hot water to your taps, which also saves water. Home improvement stores carry foam insulation designed to fit snugly around pipes.

  • Get faster delivery. A demand-controlled circulating hot water system can reduce hot water waste and speed up the time it takes hot water to reach the tap.

  • Trap the heat. Heat rises, so hot water has a tendency to rise up in the inlet and outlet pipes above the tank, which wastes heat. To prevent this, many newer water heater tanks have "heat traps," small check valves added to the pipes above the tank. If your water heater doesn't have these traps, a plumber can add them. A set of two costs about $30 plus labor and can save $15 to $30 annually on your water heating costs.

When shopping, look for

  • An Energy Star. In January 2009 the government's energy efficiency program will start labeling the most efficient water heaters as "Energy Stars." Only the five most efficient types of water heaters will be eligible: Gas storage, gas-condensing storage, gas tankless, heat pump, and solar. Energy Star will not cover the least efficient water heaters: electric storage and electric tankless.
  • Water Efficient Water Heaters

  • The right fuel source. First, find out what's available where you live and how much it costs. Options include electricity, natural gas, fuel oil, propane, solar energy, and even heat stored in the ground. Heating water with natural gas, propane, or fuel oil is usually more energy efficient and less expensive than heating with electricity. The sun's energy is free, of course, but you have to be able to handle higher upfront costs of the system. Pumps that tap the heat stored in the ground may be cost effective, too, depending on your climate and other factors.

  • A high "EF." Storage, tankless, and heat-pump water heaters are rated with an Energy Factor (EF). The higher the EF, the more efficient the unit is. (Solar and indirect water heaters use different measurements of efficiency.) The EF is a good way to compare heaters within the gas-fired group. But it's misleading when comparing gas versus electric. The EFs of electric water heaters are higher (.90+) than those of gas water heaters, but don't reflect significant energy losses when electricity is generated and distributed.

  • Appropriate size. The system's size depends on how many people live in your home, the amount of water used and the kind of equipment you are using. Keep in mind that if you make an effort to conserve hot water, you may be able to get by with a smaller, less expensive model.


  • Electric water heaters. The least efficient options are electric storage and electric tankless water heaters. If electric heating is your only option, consider a heat pump water heater.

Other Considerations

When a water heater gives out, most people replace it with a similar unit. That's fine if you have a gas water heater and you buy one of today's high-efficiency models. Beyond that, things start to get complicated. Solar water heating is the greenest option. Apart from solar, the most energy-efficient choices are gas-fired tankless water heaters with electronic ignition, heat-pump water heaters, combined space and water heaters, and gas-fired condensing storage water heaters.

  • Heaters with tanks. Most water heaters are "storage water heaters." The water is heated, then stored in a tank until needed. Eventually the water in the tank cools down and has to be reheated. Some 15% percent of a water heater's energy can be wasted this way--it's called "standby heat loss." More insulation in the tank's walls helps reduce standby heat loss.

    • In 2009, Energy Star high-efficiency sealed-combustion gas storage water heaters will have to have an EF of .62 or greater. In 2010, that goes up to .67 or greater. Also known as "power-vented" or "direct-vented," sealed combustion means that pipes bring outside air directly to the water heater's combustion chamber and vent the exhaust gases directly outside. Sealed combustion water heaters do a better job of protecting home health because there's no chance that combustion gases can get drawn into the house.

    • To increase your energy savings more dramatically, consider a gas-fired condensing storage water heater. Energy Star condensing heaters will have an EF of .80 or greater. These units are more expensive to buy and install than a high-efficiency non-condensing gas water heater. They save energy by extracting heat from gases in the flue before they are vented outside. This cools the water vapor in the flue gases to the point where it condenses into a liquid. These units require special venting and a pipe to drain the condensate to the wastewater line.

    • Electric storage water heaters are much more expensive to operate than gas (although some electric utilities offer special low rates for electric water heating).

  • Heaters without tanks. These devices (sometimes called "demand," "instantaneous," or "flash water heaters") heat water only as needed, eliminating the problem of standby loss. They provide a continuous stream of hot water, take up a lot less space, and are about 10% to 20% more efficient than storage heaters. But they're expensive--costing two to four times more to install than storage water heaters--and tend to work best for smaller households or low water users.

    • Tankless water heaters don't deliver hot water instantly. The time it takes for hot water to reach a tap is a function of how far the tap is from the water heater.

    • Each model provides a specific flow rate. Units with lower flow rates may not deliver enough hot water when there is simultaneous demand, such as when a shower and dishwasher are running at the same time. Gas tankless heaters also have a minimum flow rate and some won't turn on if you just have the tap open to a trickle.

    • Choose a gas tankless model with an electronic ignition to avoid having a pilot light on all the time wasting gas. Energy Star gas tankless water heaters will have an EF of .82 or greater.

    • Electric tankless heaters are usually the least green option, unless you have a bathroom that's infrequently used and located far from the main water heater. Then it might make sense to install a small electric tankless heater in that bathroom rather than run pipes all the way from the main heater.

    • If switching from a storage heater to tankless, the size of the gas supply line may need to be increased or the home's electrical service may need to be upgraded and new wiring installed.

  • Other options. Conventional storage water heaters dominate the market, although installations of tankless units have been growing in recent years. Some other, less common systems are listed below. To find out more about them, talk to an HVAC professional.

    • The majority of U.S. homes are heated by a forced air furnace, but if yours is heated by a boiler, consider an indirect water heater. Instead of relying on combustion to heat the household water, these units have a heat exchanger that draws heat from the boiler. Well-designed indirect water heaters can be more efficient than conventional storage water heaters.

    • Integrated space and water heating systems take the indirect water heater concept one step further. Configurations vary, but these units integrate a high-efficiency boiler and a hot-water storage tank into one appliance to provide household hot water and space heating. These units tend to cost more than separate water heaters and furnaces, and due to the complexity of their controls, some require installers with specialized skills.

    • If you have no choice but to heat your water with electricity, consider a heat-pump water heater. It uses one third the electricity of a standard electric water heater. But there are downsides: it will be much more expensive to buy and uses refrigerants that deplete the ozone layer and produce greenhouse gases. If you use a heat pump to heat and cool your house, you may be able to have it modified to also heat your water.

Benefits... your wallet
Energy-efficient water heaters typically cost more upfront but less in the long run when you factor in reduced energy bills. A tankless heater can reduce your water heating energy costs by 10% to 20% over a storage heater. the Earth
Using less hot water and choosing more efficient water heaters reduces fossil fuel depletion, CO2 emissions, and air pollution. Tankless heater and smaller storage heaters offer an additional benefit: they use less material to manufacture than large tanks.

Common Mistakes

Waiting for your water heater to fail. If your hot water dries up on the eve of your in-laws' visit, you might jump into a hasty purchase that you'll pay for in higher energy costs for years to come. Most storage water heaters last about 15 years (tankless should last about 20). If yours is approaching or has passed that age, consider replacing it now rather than waiting for it to fail. A plumber can give you an estimate of how much longer it's likely to last.

Getting Started

Choosing the most appropriate, efficient, and cost-effective water heater is a complex undertaking. The Department of Energy's Water Heating website has detailed information and worksheets that will take you through the details.

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