There are two heat elements in a dual-element water heater: one on top and one towards the bottom of the tank. When the water in the top half of the tank reaches the temperature set, the top element switches off, and the bottom element comes on to heat the remaining water. As more hot water is needed, it will continue to heat the same amount of water until all the water has been heated.
The advantage of this arrangement over a single-element heater is that less energy is required to heat a large volume of water than is required to heat a small volume. This can be important where there is no supply line available to reach temperatures above 70 degrees F (21 degrees C). Heating water to a higher temperature for use in showers or hand-washing dishes is more efficient if done in smaller quantities rather than in one large batch. A dual-element heater will continuously produce hot water as long as the top element is turned on; when it shuts off, the bottom element begins heating water again.
A third type of water heater, called a "multizone" heater, has three or more sections or zones within one container. Water is pumped from one zone to another where it is heated by electric coils or gas flames before being returned to the next zone. Each section has its own thermostat so that only the sections needing heat will have fuel injected into them.
Electric water heaters often include two sets of heating elements, top and bottom, that are powered by two different thermostats. One regulates the temperature of the water at the top of the tank, while the other regulates the temperature at the bottom. This allows the water to heat up faster at the top of the tank where it's being used, but not so fast at the bottom where it would overflow the tank.
The majority of electric water heaters sold today are controlled by one-way valve circuits. This means that when the top thermostat reaches its set point, it opens a circuit that allows electricity to flow through the heater until the lower thermostat reaches its set point. The lower thermostat then closes this circuit, stopping the flow of current through the heater.
Heaters with two-way valves work the same way except that they don't shut off power once they've been activated. This is useful for tanks that you use for hot water storage as well as for washing machines or dishwashers that may require more heat at the bottom of the tank than at the top.
One-way and two-way valve designs are available on most electric water heaters. It's important to understand how your particular model works before you start setting temperatures on your thermostats.
Heating happens in one element at a time in a dual-element system, never simultaneously. When there is cold water in the water tank, the higher thermostat will heat the upper element. The power is then sent to the lower thermostat, which warms the lower element. The hot water comes on first at the top, then flows down to fill the bottom chamber until the temperature drops again. This process continues all day long without any trouble signals from either element.
As long as neither element is receiving a signal to turn off, the system will keep pumping out heat 24 hours a day. However, if you leave a hot water heater unattended for several days, you may receive a warning signal from it. These warnings can be seen as a low water pressure signal at the valve attached to the tank or as a hissing noise when the water is turned on. Both of these problems require that you have a professional repair your heater.
The two heating components work together to guarantee that there is always hot water at the tank's top. If the water temperature at the top of the tank is lower than the temperature set by the top thermostat, the top heating element will activate and the warming process will commence. Once the top thermostat reaches its setting, it will shut off the top heater. The bottom heater stays on all time, even when the top isn't being used to keep the water at a constant temperature.
This type of heater uses magnetic valves located in the supply line to control the flow of electricity to each element. When a magnetic valve is closed, no current flows and therefore no heat is produced. When the valve is open, current flows freely and the heater works as normal. This type of valve opens toward the source of electricity (the house) instead of away from it like other types of valve. This design ensures that if one part of the heater goes out of action, the water still gets heated because it isn't affected by the malfunctioning section.
Electric water heaters with magnetic valves are more expensive to manufacture than those with other types of valves, but they are more reliable. Since they don't have moving parts, they tend to break down less often than conventional heaters do and they require less maintenance.
Advantages The dual element water heating system is the most efficient of the two. It warms water faster than a single element system because water is transferred from one end of the tank to the other, whereas a single element system only heats from the bottom up. The dual element system is also less expensive to install than a single element system.
Disadvantages Because it uses two elements instead of one, a dual element system takes up more space than a single element system. This is not a problem if you plan to install your system under the flooring or in an exterior wall, but if you want to install it inside a cabinet or frame, you will need to make sure that it does not interfere with any other appliances that you may have installed in the room.
The type of element used in a dual element system can affect how much heat it releases into the water. Quartz elements are the most efficient and cost the most. Ceramic elements are less efficient but cheaper to purchase in large quantities. Lead elements release leaching chemicals into the water when they break down over time, so they should not be used for drinking water.
There are different types of dual element systems available on the market: magnetic induction, ceramic, quartz. Each type has its advantages and disadvantages. Magnetic induction systems use electricity to create a field which then produces heat via magnetism.