Water Heaters

Tankless Water Heaters

Throw away your water heater tank and shave ten to twenty percent off your water heating bill. That savings results from elimination of standby losses -- energy lost from warmed water sitting in a tank. And, since water heating accounts for about 14 percent of the average U.S. household energy budget, this can be a significant loss.

Tankless water heaters provide hot water at a preset temperature when needed without storage, thereby reducing or eliminating standby losses. Tankless water heaters can be used for supplementary heat, such as a booster to a solar hot water system, or to meet all hot water needs.

Tankless water heaters have an electric, gas, or propane heating device that is activated by the flow of water. Once activated, the heater provides a constant supply of hot water. The maximum flow rate at a desired temperature will be determined by the capacity of the heater. Gas tankless water heaters typically have larger capacities than electric tankless water heaters.

Large units intended for whole house water heating are located centrally in the house while, in point-of-use applications, the water heater usually sits in a closet or under a sink.

Tankless water heaters are rated by the maximum flow rate at which a desired temperature rise is met. Special features may allow the user to set the delivery temperature. Efficiency is higher than an equivalent tank type water heater because standby losses are virtually eliminated. Electric tankless water heaters require a relatively high electric power draw because water must be heated quickly to the desired temperature. Residential gas models are available that can heat more than five gallons per minute by 60°F, generally more than enough for two showers to be run simultaneously. Whole house electric units typically have a capacity closer to three gallons per minute.

Solar Water Heaters

Harnessing energy from the sun to heat water is nothing new. Solar water heaters have been commercially available since the 1800s. What's new is how solar water heaters look these days. Most modern solar water heaters mount flush with a home's roof and resemble skylights. Solar water heaters are an environmentally sound way to reduce energy bills.

Solar energy can meet part or all of a home's domestic hot water needs. Geographic location, system design, collector orientation, and collector size will determine how much energy can be provided for domestic hot water heating.

Solar water heaters come in a variety of configurations. Each differs in design, cost, performance, and level of complexity. Most systems have back-up water heating such as electricity or gas. A solar water heating system usually consists of a hot water storage tank, a solar collector that absorbs solar energy, a back-up energy source, and (for forced circulation systems) a pump and controls.

There are two main types of systems: passive and forced circulation. Within each type, there are several configurations. A passive water heater consists of a water tank integrated into or located above a solar collector. In an integrated collector storage (ICS) system, also called batch water heater, the water is heated and stored inside the collector. These systems are suitable only for warm climates where there is no risk of freezing. In a passive system where the storage is separate from the collector, as water in the collector warms, water flows by natural convection through the collector to the storage tank. A forced circulation system requires a pump to move water from the storage tank to the collector. Most solar water heaters in the United States are the forced circulation type.

There are several types of solar collectors. Most consist of a flat copper plate, painted black, that has water tubes attached to the absorber plate. As solar energy falls on the copper plate and is absorbed, the energy is transferred to water flowing in the tubes. The absorber plate is mounted in a casing that has a clear covering and insulation to protect the absorber plate from heat loss. Other collectors include an integrated collector and storage system and the evacuated tube collector. Integral collector and storage systems combine the function of hot water storage and solar energy collection into one unit. Evacuated tube collectors produce higher temperature water and are more complex than flat plate collectors. Evacuated tube collectors consist of a series of tubes that contain a heat pipe to absorb solar energy and transfer it to a liquid medium. The tubes are evacuated (vacuum) so that there is very little heat loss from the tube. Most solar collectors are roof-mounted. Solar water heaters are used for domestic hot water, pool heating and space heating needs.