Water Heaters

More about Water Heaters

High-efficiency gas storage water heaters

High-efficiency gas storage water heaters work similarly to standard storage water heaters. A glass-lined steel tank is heated from below by a gas burner. The “high-efficiency” status is achieved through improved insulation, heat traps, and more efficient burners. These modifications improve efficiency by about 7.5%. Additionally, a power vent may be added to accelerate the venting of combustion gases, which increases the installation costs while simultaneously boosting savings.

Gas-condensing water heaters

Gas-condensing water heaters work very similarly to regular gas water heaters with a large tank of water being heated by a gas burner. However, in these models, the heat and conductive gases used initially to heat the water from underneath are circulated through a conductive chimney inside the water tank in on the way to being vented out the top. This essentially means that the heat energy is used twice before being released to the outside. This technology can reduce natural gas bills by more than $100/year.

Heat Pump Water Heater

Heat pumps can be used for heating water in addition to heating and cooling your home. They are not very common at this time, but use one third to one half the amount of electricity as conventional water heaters. Heat pumps can either be added on to existing hot water tanks or stand alone and use their own tank (“integral unit”). It is more common to install an air-source heat pump system that combines heating, cooling, and water heating.   Heat pumps are only really viable in regions that remain in the 40º–90ºF (4.4º–32.2ºC) range year-round. You must be able to provide at least 1,000 cubic feet (28.3 cubic meters) of air space around the water heater. [Click here for an explanation of heat pump technology] (Link to heat pump section)

Whole-home gas tankless water heater

Whole-home gas tankless water heaters provide water only when it is needed, thereby cutting costs by 30% while still delivering continuous hot water. When a hot water tap is turned on, it initiates the flow of cold water into the heater, which in turn activates the gas burner to warm the heat exchanger. The cold water is heated by passing the heat exchanger and then leaves the heater once it reaches the set temperature. Instead of constantly burning gas to maintain a large tank of hot water, tankless heaters heat water just once. Additionally, the ENERGY STAR qualified units are small and wall-mounted, and are also available for outdoor installation to save even more space. Demand water heaters produce 2-5 gallons per minute, with gas-fired producing higher flow rates than their electric counterparts. Sometimes, even the most high-powered demand water heaters cannot keep up with intensive simultaneous hot water use. Installing multiple demand units or separate units for appliances can solve this problem. Additionally, be sure to consider the gas consumed by the pilot light; some models have an intermittent ignition device (IID) that eliminates the pilot light in favor of a spark ignition. A life expectancy of 20 years is much greater than that of a conventional tank water heater, while the risk of leaks and water and damage are effectively eliminated.

Tankless coil and indirect water heater

Tankless coil water heaters feature a heating coil or exchanger that is installed in a home’s main boiler or furnace. The boiler or furnace heats the water directly whenever the hot water is turned on the home. This system is dependent upon the furnace being active, and therefore is only a worthwhile investment in colder climates.

Indirect water heaters require a storage tank, yet still utilize the furnace or boiler to heat a fluid that is then circulated in the storage tank to heat the water. Provided that the boiler or furnace is high-efficiency and the tank is well-insulated, this approach can be a very energy efficient way of heating water, as the tank allows the furnace or boiler to be turned on and off less often than the tankless option.

Solar Water Heaters

Solar water heaters are available in a wide range of designs and utilize varying technologies with the ultimate purpose of capturing the sun’s thermal energy to heat water. The heaters are usually classified by the type of collector (the manner in which sun’s energy is captured) and the circulation (the manner in which this energy is transferred to your home’s water).

There are three main types of collectors:

1)      Batch collectors (also called Integrated Collector-Storage systems): This technology heats water in “batches”—water is stored in dark tanks and held until drawn. The water can become very hot during periods of low water usage, and therefore requires a tempering valve to add cold water before it reaches the tap. They are generally not recommended for cold climates because of their incompatibility with the closed-loop circulation system.

2)      Flat-plate collectors: This set-up includes a series of parallel copper tubes sized to fit flat absorber plates. The plates are housed within an insulated box that is covered in tempered glass and insulated along the sides and bottom to minimize heat loss. Heat is transferred to liquid that passes through pipes attached to the absorber plate. They are generally sized one-half to one-square foot per gallon of one-day’s hot water use.

3)      Evacuated tube collectors: This technology is the most efficient manner of heating water using the sun’s energy. High efficiency allows the collector to work well in overcast conditions and in cold temperatures (even sub-zero). The apparatus is comprised of a series of tubes. Each individual tube is made of an inner glass or metal tube that contains the water or heat transfer fluid. That tube is in turn surrounded by another larger glass tube. The space between the two tubes is a vacuum, providing very effective insulation to prevent heat loss. These systems are among the most expensive on the market.

Additionally, there are four types of circulation systems:

1)      Direct systems: Direct systems circulate the water through the solar collectors to heat it. Upon heating, the water is either used directly, sent to a storage tank, or sent to a tankless water heater. Generally, these systems are intended for climates in which there is no chance of freezing.

2)      Closed-loop (indirect) systems: These systems use a non-freezing liquid as the medium to transfer energy from the collector to water being held in a tank. This type of system is preferred in climates with lower temperatures.

3)      Active (forced-circulation) systems: These systems employ electric pumps, valves, and controllers to move water throughout the system.

4)      Passive systems: As the name suggests, these systems rely upon natural convection to move the water to the storage tank as its temperature increases.

The energy efficiency of a solar water heater is indicated by the solar energy factor (SEF) and the solar fraction (SF). The SEF is calculated by dividing the energy developed by the system by the electrical or gas energy put into the system. A higher number means a higher efficiency. The SF is the proportion of a home’s total hot water load (delivered hot water plus standby losses) generated by the solar water heater.