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Star Energy Water Heaters

The ENERGY STAR program empowers consumers to make smart energy choices that will save money, and energy, and reduce carbon emissions.

Star Energy Water Heaters

In five years, the new water heater criteria are expected to save Americans consumers $823 million in utility costs, avoid 4.2 million tons of carbon dioxide emissions, and achieve cumulative energy savings of more than 3.9 billion kilowatt-hours and 270 million therms of natural gas – enough energy to power more than 375,000 homes for a year.

Five water heating technologies are eligible to use the ENERGY STAR® label:

* High-efficiency gas storage water heaters employ the same technologies as standard gas storage water heaters: a glass-lined steel tank is heated by a burner located at the bottom of the tank. ENERGY STAR® labeled models increase efficiency by incorporating better insulation, heat traps, and more efficient burners.

* Gas condensing water heaters work much like regular gas water heaters. However, instead of venting the combustion gases directly outside, heat from those gases is further transferred to the water thus increasing efficiency.

* Whole-home gas tankless water heaters apply the same principle to heat water as standard gas water heaters, but without a storage tank. They save energy by heating water only when needed, eliminating energy lost during standby operation.

* Heat Pump Water Heater (HPWH) technology uses electricity to move heat from one place to another instead of generating heat directly. Much like a refrigerator working in reverse, a HPWH uses liquid refrigerant to take the heat from surrounding air and transfer it to water in an enclosed tank.

* Solar water heaters come in a wide variety of designs, all using the sun’s thermal energy to heat water.

Solar Water Heaters

Solar water heaters—also called solar domestic hot water systems—can be a cost-effective way to generate hot water for your home. They can be used in any climate, and the fuel they use—sunshine—is free.

How They Work

Solar water heating systems include storage tanks and solar collectors. There are two types of solar water heating systems: active, which have circulating pumps and controls, and passive, which don't.

Most solar water heaters require a well-insulated storage tank. Solar storage tanks have an additional outlet and inlet connected to and from the collector. In two-tank systems, the solar water heater preheats water before it enters the conventional water heater. In one-tank systems, the back-up heater is combined with the solar storage in one tank.

Three types of solar collectors are used for residential applications:

Flat-plate collector

Glazed flat-plate collectors are insulated, weatherproofed boxes that contain a dark absorber plate under one or more glass or plastic (polymer) covers. Unglazed flat-plate collectors—typically used for solar pool heating—have a dark absorber plate, made of metal or polymer, without a cover or enclosure.

Integral collector-storage systems

Also known as ICS or batch systems, they feature one or more black tanks or tubes in an insulated, glazed box. Cold water first passes through the solar collector, which preheats the water. The water then continues on to the conventional backup water heater, providing a reliable source of hot water. They should be installed only in mild-freeze climates because the outdoor pipes could freeze in severe, cold weather.

Evacuated-tube solar collectors

They feature parallel rows of transparent glass tubes. Each tube contains a glass outer tube and metal absorber tube attached to a fin. The fin's coating absorbs solar energy but inhibits radiative heat loss. These collectors are used more frequently for U.S. commercial applications.

There are two types of active solar water heating systems:

Direct circulation systems

Pumps circulate household water through the collectors and into the home. They work well in climates where it rarely freezes.

Indirect circulation systems

Pumps circulate a non-freezing, heat-transfer fluid through the collectors and a heat exchanger. This heats the water that then flows into the home. They are popular in climates prone to freezing temperatures.

Illustration of an active, closed loop solar water heater. A large, flat panel called a flat plate collector is connected to a tank called a solar storage/backup water heater by two pipes. One of these pipes is runs through a cylindrical pump into the bottom of the tank, where it becomes a coil called a double-wall heat exchanger. This coil runs up through the tank and out again to the flat plate collector. Antifreeze fluid runs only through this collector loop. Two pipes run out the top of the water heater tank; one is a cold water supply into the tank, and the other sends hot water to the house.

Passive solar water heating systems are typically less expensive than active systems, but they're usually not as efficient. However, passive systems can be more reliable and may last longer. There are two basic types of passive systems:

Integral collector-storage passive systems

These work best in areas where temperatures rarely fall below freezing. They also work well in households with significant daytime and evening hot-water needs.

Thermosyphon systems

Water flows through the system when warm water rises as cooler water sinks. The collector must be installed below the storage tank so that warm water will rise into the tank. These systems are reliable, but contractors must pay careful attention to the roof design because of the heavy storage tank. They are usually more expensive than integral collector-storage passive systems.

Illustration of a passive, batch solar water heater. Cold water enters a pipe and can either enter a solar storage/backup water heater tank or the batch collector, depending on which bypass valve is opened. If the valve to the batch collector is open, a vertical pipe (which also has a spigot drain valve for cold climates) carries the water up into the batch collector. The batch collector is a large box holding a tank and covered with a glaze that faces the sun. Water is heated in this tank, and another pipe takes the heated water from the batch collector into the solar storage/backup water heater, where it is then carried to the house.

Solar water heating systems almost always require a backup system for cloudy days and times of increased demand. Conventional storage water heaters usually provide backup and may already be part of the solar system package. A backup system may also be part of the solar collector, such as rooftop tanks with thermosyphon systems.

Since an integral-collector storage system already stores hot water in addition to collecting solar heat, it may be packaged with a demand (tankless or instantaneous) water heater for backup.

For more information about solar water heating system components, see the following information:

* Heat Exchangers for Solar Water Heating Systems * Heat-Transfer Fluids for Solar Water Heating Systems

Selecting a Solar Water Heater

Before you purchase and install a solar water heating system, you want to do the following:

* Consider the economics of a solar water heating system

* Evaluate your site's solar resource

* Determine the correct system size

* Determine the system's energy efficiency

* Estimate and compare system costs

* Investigate local codes, covenants, and regulations

The proper installation of solar water heaters depends on many factors. These factors include solar resource, climate, local building code requirements, and safety issues; therefore, it's best to have a qualified, solar thermal systems contractor install your system.

After installation, properly maintaining your system will keep it running smoothly. Passive systems don't require much maintenance. For active systems, discuss the maintenance requirements with your system provider, and consult the system's owner's manual. Plumbing and other conventional water heating components require the same maintenance as conventional systems. Glazing may need to be cleaned in dry climates where rainwater doesn't provide a natural rinse.

Regular maintenance on simple systems can be as infrequent as every 3–5 years, preferably by a solar contractor. Systems with electrical components usually require a replacement part after or two after 10 years. For more information about system maintenance, see the following:

* Solar Water Heating System Maintenance and Repair

* Solar Water Heating System Freeze Protection

* Scaling and Corrosion in Solar Water Heating Systems

When screening potential contractors for installation and/or maintenance, ask the following questions:

Does your company have experience installing and maintaining solar water heating systems?

Choose a company that has experience installing the type of system you want and servicing the applications you select.

How many years of experience does your company have with solar heating installation and maintenance?

The more experience the better. Request a list of past customers who can provide references.

Is your company licensed or certified?

Having a valid plumber's and/or solar contractor's license is required in some states.

Contact your city and county for more information. Confirm licensing with your state's contractor licensing board. The licensing board can also tell you about any complaints against state-licensed contractors.

For contractor information, see the Professional Services resources listed on the right side of this page (or below if you've printed it out).

Improving Energy Efficiency

After your water heater is properly installed and maintained, try some additional energy-saving strategies to help lower your water heating bills, especially if you require a back-up system. Some energy-saving devices and systems are more cost-effective to install with the water heater. Other Water Heater Options:

* Conventional storage water heaters

* Demand water heaters

* Heat pump water heaters

* Tankless coil and indirect water heaters

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