Exploring Hot Water Heater Options
Demand (Tankless or
Instantaneous) Hot Water Heater Options
It costs 20% or more of an average
household’s annual energy expenditures to meet hot water heater demands. The yearly operating costs for
conventional gas or electric storage tank hot water heater options average $200 or
$450, respectively.
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Storage tank-type models raise and maintain the temperature to the temperature setting on the tank (usually between
120° -140° F (49° -60° C). Even if nothing is drawn from the tank
(and cold h2o enters the tank), it will operate periodically to
maintain the temperature. This is due to "standby losses":
the heat conducted and radiated from the walls of the tank—and in
gas-fired models—through the flue pipe. These standby losses
represent 10% to 20% of a household’s annual costs. One
way to reduce this expenditure is to use a demand (also called
"tankless" or "instantaneous") models.
Demand models are common in Japan and Europe.
They began appearing in the United States about 25 years ago. Unlike
"conventional" models, tankless models heat
water only as it is used, or on demand. A tankless unit has a heating
device that is activated by the flow of h2o when a valve is
opened. Once activated, the unit delivers a constant supply. The output of the
unit, however, limits the rate of the heated flow.
Gas and Electric Models
Demand units are available in propane (LP),
natural gas, or electric models. They come in a variety of sizes for
different applications, such as a whole-house units, a
source for a remote bathroom or Jacuzzi, or as a boiler to provide for a home heating system. They can also be used as a booster for
dishwashers, washing machines, and a solar or wood-fired domestic system.
You may install a demand water heater centrally or at
the point of use, depending on the amounts required. For
example, you can use a small electric unit as a booster for a remote
bathroom or laundry. These are usually installed in a closet or underneath
a sink. The largest gas units, which may provide all the needs
of a household, are installed centrally. Gas-fired models have a higher output than electric models. As with many tank
models,
even the largest whole house tankless gas models cannot supply enough for simultaneous, multiple uses
(i.e., showers and
laundry). Large capacity users, such as the clothes washer and
dishwasher, need to be operated separately. Alternatively, separate demand
heating units can be installed to meet individual demands, or two
or more units can be connected in parallel for simultaneous demand. Some manufacturers of tankless heaters claim that
their product can match the performance of any 40 gallon (151 liter) tank
unit.
Life Expectancy
Most tankless models have a life expectancy of more than
20 years. In contrast, storage tank models last 10 to 15 years.
Most tankless models have easily replaceable parts that can extend their
life by many years more.
Bibliography
This list does not cover all available sources of
information on tankless water heater units, nor is the mention of any
publication, product, service, or organization to be considered a
recommendation or endorsement.
For additional articles on this subject use the
following link
http://www.eere.energy.gov/consumerinfo/refbriefs/bc1.html
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