In residences, the hot water is used for bathing and cleaning. In some buildings, the hot water serves to sterilize equipment that is used by the general public. Besides comfort, hot water serves a vital role in maintaining good health. To serve this role, the hot water must be produced at an appropriate temperature.
Most homes and buildings have a tankless hot water heater, a hot water heater with a storage tank, a hot water booster tank, or an indirect-fired hot water heater. A comparison of the different types of hot water systems is found later on this page.
The Licensed Professional Engineers (who are also Licensed Home Inspectors) at Heimer Engineering evaluate the hot water system in the home or building you are considering purchasing and advises you if it is sufficient. You are also advised of the need to budget for upcoming replacement of the hot water heater.
Hot Water Temperature
Hot water that would scald in seconds at 140 degrees Fahrenheit will take minutes to cause the same level of injury at less than 120 degrees Fahrenheit.In residential applications, the temperature of the hot water should be around 120 degrees Fahrenheit, although some dishwasher manufacturers recommend 130 degrees Fahrenheit to assure that the dishes will be properly cleaned and sterilized. Lower temperatures are recommended by others to reduce the risk of scalding and reduce energy consumption. A lower temperature, however, increases the risk of bacteria growth.
Hot water that would scald in seconds at 140 degrees Fahrenheit will take minutes to cause the same level of injury at less than 120 degrees Fahrenheit. Many hot water systems produce hot water at well over 130 degrees Fahrenheit. The risk of scalding or serious burns, especially to children and elderly people, is high.
Hot Water Heater Life Expectancy
Hot water heater life expectancy varies dramatically depending on the type of hot water heater. A tankless hot water heater can last as long as the heating system in which it is mounted, although effectiveness may diminish over time. An automatic storage hot water heater, hot water booster tank, or an indirect-fired hot water heater typically lasts from seven to 15 years.
Tankless Hot Water Heaters
A tankless hot water heater heats the water by circulating it through coils inside a boiler.A tankless hot water heater heats the water by circulating it through coils inside a boiler. As the water circulates through the coils, it is heated.
Tankless hot water heaters often suffer from performance problems, especially as they age. Many systems start out at an initial temperature hot enough to scald. After running for a short time, this hot temperature may fall to a relatively low temperature. To help overcome this problem, many people install hot water booster tanks in conjunction with a tankless hot water heater.
A variation of the tankless hot water heater is the instant hot water heater, sometimes called the demand hot water heater. In an instant hot water heater, water passes over a heat exchanger. The heat exchanger is kept warm, usually by a gas flame or electric coil.
See the hot water heater comparison below for more information on tankless hot water heaters.
Hot Water Booster Tanks
A hot water booster tank works in conjunction with a tankless hot water heater. Most hot water booster tanks are small hot water heaters. The water is pre-heated in the tankless hot water heater. The heated water than circulates into the hot water booster tank. The hot water booster tank stores the hot water, and warms it if necessary. This increases the amount of available hot water, although at the cost of greater energy consumption. Often, hot water boosted booster tanks are electric, which makes them expensive to operate.
See the hot water heater comparison below for more information on hot water booster tanks.
Hot Water Heaters With Storage Tanks
When many people say hot water heater, they are referring to a single unit that both heats and stores the water.When many people say hot water heater, they are typically referring to a single unit that both heats and stores the water. This type of unit is sometimes called an automatic storage hot water heater. This type of unit must have some method of heating the water (typically oil, gas, or electricity) along with a tank to store the heated water.
See the hot water heater comparison below for more information on hot water heaters with storage tanks.
Indirect-Fired Hot Water Heaters
An indirect-fired hot water heater consists of a storage tank, a circulatory pump, and a boiler that serves as a heat source. The boiler (and the water is contains) is kept hot. When the storage tank of hot water falls below a certain temperature, an aquastat activates the circulatory pump. The boiler-heated water is circulated through coils in the hot water storage tank. This process heats the water in the storage tank. The water heated in the boiler never comes in contact with the water in the storage tank.