TYPES OF WATER HEATERS

Storage water heaters are by far the most common type of water heater in the U.S. today. Ranging in size from 20 to 80 gallons (or larger) and fueled by electricity, natural gas, propane, or oil, storage water heaters heat water in an insulated tank. When you turn on the hot water tap, hot water is pulled out of the top of the water heater and cold water flows into the bottom (through a "dip tube" from the top) to replace it. Because heat is lost through the flue and the walls of the storage tank (this is called standby heat loss), energy is consumed even when no hot water is being used. New energy-efficient storage water heaters have higher levels of insulation around the tank and one-way valves where pipes connect to the tank, substantially reducing standby heat loss.

Demand (or instantaneous) water heaters eliminate the storage tank by heating water only when there is a call for hot water. These units are growing in popularity in the U.S. The energy consumption of these units is generally lower since standby losses from the storage tank are eliminated. Demand water heaters with enough capacity to meet household needs are gas- or propane-fired. They have three significant drawbacks for some applications: Large simultaneous uses (two showers and the clothes washer, for example) may challenge their capacity, particularly in winter,when the inlet water is coldest. They will not turn on unless the hot water flow is ½ - 3/4 gallon/minute. Retrofit installation can be very expensive. Finally, because the efficiency tests were not developed with these designs being considered, it is not known if the "EF" accurately estimates energy consumption. If you choose a tankless unit, look for one eligible for 2006-2007 federal tax credits (EF 0.80 (Gas) or EF 0.20 (Electric)).

Solar water heaters use energy from the sun to heat water. Solar water heaters are designed to serve as preheaters for conventional storage or demand water heaters. While the initial cost of a solar water heater is high, it can save a lot of money over the long term. Solar water heaters are much less common than they were during the 1970s and early 1980s when they were supported by tax credits, but the units available today tend to be considerably less expensive and more reliable. At today’s prices, solar water heaters compete very well with electric and propane water heaters on a life-cycle cost basis, though they are still usually more expensive than natural gas.

WATER HEATER EFFICIENCY

The energy efficiency of a storage water heater is indicated by its energy factor (EF), an overall efficiency based on the use of 64 gallons of hot water per day. The first national appliance efficiency standards for water heaters took effect in 1990. New standards, which took effect in January 2004, increased the minimum efficiency levels of water heaters.

The most efficient gas-fired storage water heaters have energy factors ranging from 0.63 to 0.67, corresponding to estimated gas use below 170 therms/year. Condensing water heaters have energy factors as high as 0.86. The most efficient electric storage water heaters have energy factors ranging between 0.93 and 0.95, resulting in estimated annual energy use below 4,725 kWh/year. There is little difference between the most efficient electric resistance storage water heaters and the minimum efficiency standard. UPGRADING YOUR EXISTING WATER HEATER

Even if you aren’t going to buy a new water heater, you can save a lot of energy and money with your existing system by following a few simple suggestions.

* Conserve Water: Your biggest opportunity for savings is to use less hot water. In addition to saving energy (and money), cutting down on hot water use helps conserve dwindling water supplies, which in some parts of the country is a critical problem. A family of four each showering five minutes a day can use about 700 gallons per week—a three-year drinking water supply for one person! Water-conserving showerheads and faucet aerators can cut hot water use in half. That family of four can save 14,000 gallons of water a year and the energy required to heat it.

* Insulate Hot Water Pipes: Insulating your hot water pipes will reduce losses as the hot water is flowing to your faucet and, more importantly, it will reduce standby losses when the tap is turned off and then back on within an hour or so. A great deal of energy and water is wasted waiting for the hot water to reach the tap. Even when pipes are insulated, the water in the pipes will eventually cool, but it stays warmer much longer than it would if the pipes weren’t insulated.

* Lower the Water Heater Temperature: Keep your water heater thermostat set at the lowest temperature that provides you with sufficient hot water. For most households, 120°F water is fine (about midway between the “low” and “medium” setting). Each 10°F reduction in water temperature will generally save 3–5% on your water heating costs. When you are going away on vacation, you can turn the thermostat down to the lowest possible setting, or turn the water heater off altogether for additional savings. With a gas water heater, make sure you know how to relight the pilot if you’re going to turn it off while away.

SELECTING A NEW WATER HEATER

Whether you’re replacing a worn-out existing water heater or looking for the best model for a new house you’re building, it pays to choose carefully. Look for a water heater that satisfies your hot water needs and uses as little energy as possible. Often you can substantially reduce your hot water needs through water conservation efforts.

* Think About a Replacement Now: If you're like most people, you’re unlikely to go out looking for a water heater until your existing one fails, leaving little time to look for a water heater that most appropriately fits your needs and offers the highest level of energy efficiency. A much better approach is to do some research now. Figure out what type of water heater you want—gas or electric, storage or demand, stand-alone or integrated with your heating system, etc. Then, figure out the proper size for your household.

* Sizing a Water Heater: The capacity of a water heater is an important consideration. The water heater should provide enough hot water at the busiest time of the day. The ability of a storage water heater to meet peak demands for hot water is indicated by its "first hour rating." This rating accounts for the effects of tank size and the speed by which cold water is heated. . Demand water heaters should be sized according to the required gallons per minute (gpm) flow rate and temperature rise required for your largest expected hot water fixture (usually a shower).With solar water heaters, you should discuss your requirements carefully with the solar water heating salesperson. You will need to size both the solar hot water system itself and the back-up electric or gas water heater. It generally makes the most sense to size a solar water heater to provide two-thirds to three-fourths of your total demand, and provide the rest with a back-up system.

* Fuel Options: What type of fuel makes the most sense for your water heater? If you currently have an electric water heater and natural gas is available in your area, a switch might save you a lot of money. Before you rule out electricity, though, check with your utility company. It may offer special off-peak rates that make electricity a more attractive option.