The average hot water heater accounts for 25% of the home's total energy use. With rising energy prices, it just makes sense to learn a little more about these units. There are various types available but the most common is the storage type water heater. This is where a tank of water is heated by a built in burner or electric element to a set temperature and maintained at that temperature until hot water is required at a tap.
These units have an energy efficiency rating that is referred to as the energy factor (EF). This is a relative rating of the efficiency and ranges from about .5 to 1.0. In simple terms, the higher the EF the less it will cost to operate.
Another rating of these units is their first hour rating. This is a measure of how much hot water the unit can provide in the first hour you turn it on. It takes into account the amount of water stored and how fast it can heat it.
A hot water heater is also rated according to its storage capacity. This is the number of gallons of water the units can hold.
Standard units can use gas, electric, oil, geothermal, or the sun to heat the water. The energy source you choose should be based on the price and availability of the energy source as well as up front cost.
They all operate in the same basic way. A thermostat senses the temperature of the water inside the tank. It turns the fuel on and off as required to maintain a set temperature. That temperature is adjustable to suit the tastes of the customer.
These units have some added components for safety and to make them last longer. First, they have a safety feature that is called a temperature/pressure relief valve. This is a valve that opens to relieve the pressure in the tank in case of a malfunction. The outlet of the valve is piped down to within a few inches of the floor. This is to prevent injury and damage if the valve opens. The water released when the valve opens will be extremely hot and may flash to steam.
Another safety feature that has been implemented in the United States is called flammable vapor ignition resistant (FVIR) technology. This is basically design features that are integrated into a hot water heater to prevent flammable vapors such as gasoline in a garage from entering the unit and igniting. The technology usually includes three parts. The first part is called the flame arrestor plate and allows combustion air to enter the unit while preventing flames from escaping downward and igniting vapors. The second part is typically called a thermal cutoff switch. This is a temperature sensor located near the burner that opens to shut the gas off. This will usually occur when adequate combustion air is not available. this will cause the burner flames to droop and the cutout to open. The final part is usually a LDO screen. This is basically an air filter that is installed to prevent the combustion air openings from becoming clogged by lint, dust, and oil. **HOT TIP** If your unit has this feature, the screen will require periodical cleaning.
Most storage units have what is called a sacrificial anode. This is a metal rod that is suspended in the tank. Minerals that are naturally in the water interact with metal and can eat away the metal. This anode provides a place for the reaction to occur without damaging the tank.
One big disadvantage of this type of hot water heater is that, as the tank of water sits in your home, it cools off. This is referred to as stand by heat loss. Then the heater has to turn on to heat the water back to temperature. This wastes energy dollars!
If the insulation value on your tank is less than R-24, it is a good idea to install a water heater blanket. This will help to minimize the standby losses and therefore save you money. Water heater blankets are available in many stores or you can even make your own. If you purchase one, get one with at least an R-8 insulation rating.
If you have an electric unit, you can also install a timer that will help to lower the standby losses. The timer is set to only maintain the water temperature at specific times during the day. They are available at many hardware and home improvement stores for less than $50. The timers can save you 5-10% on your water heating costs which will pay for the timer very quickly.
In warmer climates, a heat pump water heater can be used to increase the efficiency of your electric hot water heater. These systems combine an air source heat pump with your existing water heater or you can purchase a stand-alone unit that contains the storage tank and heat pump unit together. When the thermostat on the water heater senses the need for heat, the heat pump is energized. The heat pump utilizes a refrigerant system to remove heat from the air in the home and deliver that heat to the water in the tank. These units provide between 1/2 and 3/4 of a ton of air conditioning as an added benefit.
Some very small units are referred to as point of use or instantaneous water heaters. There are two types of these units. The first type are often called "mini-tank" units. They have a small storage tank to store from about 2.5 gallons to 6 gallons of hot water. The other type is a small electric tankless unit.
These units are often used at a sink where they are mounted in the cabinet below. Their main advantage is that water is not wasted while waiting for it to heat up. The units without a tank are a little bit more efficient because they only heat the water as it is needed.
A modern variation on the traditional storage type is the indirect fired hot water heater. Like the traditional storage type, these units have a tank of water that is heated. The main difference with these units is that they have a coil inside of them instead of a burner or electric element. This coil or coils is then connected to another source of hot water or a water/anti-freeze mixture. The water inside of the coil can be heated in a variety of ways such as from solar panels, a heating boiler, a geothermal hvac system, or many other ways.
The other main type of hot water heater is referred to as a tankless system. They are also called demand water heaters. As the name implies, these units do not maintain a tank of water at temperature. This eliminates the stand by losses and saves money and energy. They are available in gas or oil fired units or electric models.
These systems use a flow sensor and a temperature sensor. When the unit senses the flow of water, it checks the temperature and turns on the heat as required. The heat can be produced by burning gas or oil, or with electricity.
Some specialized units are commonly called electric showers. Although it may sound dangerous, these units have an electric heater built in to the shower system. When flow is sensed, the electric element is turned on and the water is heated as needed. As long as the units are properly installed and grounded, they are an energy saving option for the bath. The latest units use microprocessor controls and can remember your favorite flow and temperature settings. These features ensure that you have a comfortable shower but also save water and electricity in the process.
The latest innovation is a microwave hot water heater. These units use the same technology that is found in a cooking microwave to provide hot water on demand.
These units are rated by their efficiency, heat input rate, and the amount of water flow. It is very important to select the proper size unit.
Some of these units are a part of the home's heating system. They are referred to as combination boilers or combi boilers for short.