Hot Water and Hot Water Heaters

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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.

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.

Heimer Engineering evaluates the hot water system in your home or building and advises you if it is sufficient. You are also advised of the need to budget for upcoming replacement. The written cost analysis in the engineering report helps you plan for the future.

Hot Water Temperature

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. Heimer Engineering's Engineers measure the hot water temperature and advise you of hazards.

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 the heating system in which it is mounted, although effectiveness may diminish over time. A hot water heater, hot water booster tank, or an indirect-fired hot water heater typically lasts from seven to 15 years. Heimer Engineering evaluates the hot water system, and advise you of remaining life expectancy.

Tankless Hot Water Heaters

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 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.

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.

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 must have some sort of energy source along with a tank to store the heated water.

Most hot water heaters use oil, gas, or electricity as their source of fuel. The size of the storage tank typically varies between 30 gallons and 120 gallons, depending on the type of fuel used and the amount of hot water needed. Heimer Engineering evaluates both the fuel and the hot water demands to determine if the hot water heater is sufficient in size.

Indirect-Fired Hot Water Heaters

An indirect-fired hot water heater consists of a storage tank, a circulator 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 circulator 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.

In the greater New York area (with its seven-month heating season), an indirect-fired hot water heater my be less expensive to operate than a separate hot water heater. See the hot water heater comparison below for more information on indirect-fired hot water heaters.

Comparison of Hot Water Heaters

Type	Advantages	Disadvantages
Tankless Hot Water Heaters Demand Hot Water Heaters	Quickly heats hot water Unlimited hot water availability (at a slow flow rate)	Potential temperature fluctuations during use Risk of scalding due to temperature fluctuations Boiler must be on all year Effectiveness deteriorates with age Requires periodic cleaning to maintain performance
Hot Water Storage Tank (Used with a tankless hot water heater)	Can improve performance of a marginal tankless hot water heater May be less expensive than replacing a tankless hot water heater	Very slow to reheat when the hot water is depleted Risk of scalding hot water
Hot Water Booster Tank	Can improve the performance of a marginal tankless hot water heater	Depending on design, may be slow to reheat when hot water is depleted Risk of scalding hot water Requires fuel or electricity, which increases the cost of operation
Oil-Fired Hot Water Heater	Hot water is heated quickly Can be used in areas not served by gas	Highest cost of installation Oil requires delivery Oil price fluctuations Older equipment can be noisy, dirty, and difficult to maintain Risk of an oil leak and environmental contamination Occasional odors Risk of puffbacks Electricity to run oil burner adds to cost of operation
Gas-Fired Hot Water Heater	Relatively low cost of installation Requires minimal routine maintenance Plentiful gas supply is assured by the local gas supplier Equipment is quiet	Heats water much slower than oil Limited choice of gas suppliers Even if you can choose a different gas supplier, the gas will be only delivered by one company, reducing price competition Gas may not be available in your area
Electric Hot Water Heater	Can be installed where no oil or gas is available, such as in an apartment Plentiful supply of electricity is assured by local electricity supplier Requires minimal routine maintenance Does not require ventilation Relatively low cost of installation Equipment is quiet	Very high expense, especially in the greater New York area Hot water heating is extremely slow
Indirect-Fired Hot Water Heater	Produces ample hot water Requires minimal routine maintenance Can be located far from the boiler and in an unvented area Relatively low cost of operation	Reduced hot water availability during the heating season

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This page was last reviewed on February 26, 2008.
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