Introduction
The conventional water heater, a unit most people are accustomed to seeing, is a called a tank type water heater. A hot water heater, regardless of type, produces domestic hot water meaning hot water for the sinks, tubs, washing machine, etc., not to heat the temperature of the air within the home. Because both domestic and some central heating systems provide hot water, this often leads to confusion. Additionally, with the use of central heating systems to also produce domestic hot water in some instances, the confusion becomes even greater. Additionally, remember that a hot water boiler heats a home with hot water at radiators, baseboard and convectors. A furnace heats hot air and circulates that hot air through ducting and registers.
Tank Type Water Heaters
The typical residential tank type water heater heats water for domestic use. This type of water heater holds 30, 40 or 50 gallons however smaller and larger sizes are available for more specific uses. The conventional tank type water heater is powered by natural or propane gas, oil or electric and may represent a large portion of the energy use within a home. Cold water flows into the bottom of the tank and hot water flows out of the top. The newer high efficiency tank type heaters have adopted energy conservation improvements such as greater insulation to reduce standby loss, reduction of flue (chimney) heat loss and burning fuel more efficiently. Another improvement that has become somewhat universal is a heat trap. A heat trap is a device that prevents hot water from rising up the hot water supply line, cooling and returning back into the heater, reducing the temperature and adding to standby heat loss. The energy efficient tank type water heaters that have obtained the greatest efficiency in fuel consumption are powered by natural or propane gas. Oil, being a less refined fuel, has seen less efficiency increases, and electric use has seen the least increase in efficiency. One exception concerning electric use is that the heat pump tank type water heaters are quite efficient using electric as fuel. Heat pump systems are complex and would require a rather long explanation of function and configuration, but simply, heat pump water heaters use refrigerant to extract heat from the air and then transfers that heat being extracted to produce domestic hot water. If certain components of the system are placed outside in a warm climate, it is very efficient. When placed outside, in cold or cool climates, efficiency drops dramatically during cold temperature periods. By placing certain components at the interior, this would require heating the surrounding air resulting in a significant decrease in efficiency.
On Demand Water Heaters
Another efficient method of heating domestic hot water is an on demand water heater. Natural gas, LP gas or electric is used as a fuel. Sizing is critical as there is a maximum amount of hot water that will be heated, anywhere from 2 to 5 gallons per minute. With a tank type heater, the temperature will remain constant at the faucets until the tank is emptied, assuming the pressure is good. But with on demand units, the faucet temperature will vary depending on two factors; the number of faucets being used simultaneously and the maximum amount of hot water that the unit is capable of producing. Depending on size, the smallest units may be sufficient for a single lavatory use only, whereas a large unit may allow for showering and kitchen sink use simultaneously with adequate hot water temperatures. With on demand heaters, a minimum amount of water must flow through the unit to initiate the heat source and further to allow the unit to heat the water as it passes. As this type unit does not maintain hot water, only produce hot water as needed, no standby heat loss occurs. This design and function results in a substantial increase in efficiency. Homeowners being conscious and careful with planning to spread out what is often concentrated hot water use, may experience significant fuel savings. An example of energy savings would be a home with a large jetted tub. Usually two medium or one large tank type heater is needed to fulfill the required amount of hot water needed for a single tub use. Therefore standby heat loss for tank type systems is significant for a home with jetted tubs as most tubs are only occasionally used. The additional production of hot water is necessary for the jetted tub but remains unused the majority of the time. Building design also influences decisions. Consider that in a sprawling or multi-story building with any single heating unit placed in the basement, the time it takes to draw the water to the faucet being used, may be considerable. Unless planned for, all that unheated water must be flushed from the system before the hot water arrives, and that flushed water, is generally wasted. If water is scarce, as it is in many parts of the country, this should be taken into consideration. By placing on demand units in close proximity to the faucet being used, it would allow a more rapid response and ultimately conserve water.
Indirect Fired water Heaters
If an oil fired central hot water heating system is already present or planned in the home, another option is an indirect fired water heater installation for domestic hot water. The indirect fired water heater is an insulated tank installed adjacent to the boiler. Indirect fire water heaters are used with oil fired central systems due to the fast production of heated water whereas gas fired systems are slow to produce hot water and generally not used with indirect fired systems. The indirect fired water heater is installed as a separate zone, circulating hot water from the boiler to a coil inside the indirect fired water heater. The heat is then transferred to the water in the tank. As the indirect fired water heater has a separate thermostat, the boiler will selectively produce heat for that tank only. The system will not automatically send hot water to the radiators wasting heat, unless another control signals it necessary. These systems are quite efficient in domestic hot water production especially in the winter when a boiler is already functioning.
Summary
Politicians are not the only people good with statistics so make sure you do your homework; compare the pros and cons, and effectiveness of the different type of units. Be sure to discuss any considerations with your mechanical system contractor before you make a substantial purchase. The initial purchase cost and cost to maintain the unit should be taken into account. Sizing a water heater is also important and future use should be considered as, if kept well maintained, a water heater will provide more than a decade of service. Recovery rate may be important with electric slow, gas moderate and oil the fastest. The size of the tank type heater or the quantity of hot water that an on demand heater produces is important. While waiting for a water heater to recover temperature may be frustratingly slow, a water heater that heats excessive amounts of unused water around the clock is expensive. For example, a retired couple will use less hot water than a family of four. Also, the retired couple is able to spread out hot water use throughout the day whereas a growing family of four will concentrate use to before and after school and work.Â
Tank type heaters generally last from 8 to 12 years or more with good maintenance. On demand heaters are expected to last 20 years or more. Good quality indirect heaters are often made of stainless steel that should last almost indefinitely. Water supply with high mineral content should be evaluated prior to any type heater to determine what effect that may have on any type of hot water heaters’ performance and service life.
Many improvements may be performed on any water heater system to lower the fuel cost, insure energy savings and hot use itself should also be planned accordingly. Provide additional insulation at the water heater and the hot water supply piping. Install the heat traps as described previously, even on water heaters currently in use. Lower the water temperature in the heater from 120 to 110 degrees. Replace aged top loading washing machines with efficient front loading models. Modern front loading washers use significantly less hot and cold water and spin much more water out of the clothes reducing dryer fuel use. Also, use more cold/cold and cold/warm cycles at the washer when clothes are not heavily soiled. Lower both hot and cold water use by updating with newer fixtures and faucets throughout the building that improve water flow effectiveness. Â Electric water heaters can be provided with timers to reduce standby heat loss by not heating water at night or when at work or school but may be set to heat the hot water for use upon arrival or waking. Even older less efficient water heaters may be made more efficient with these improvements.
