Energy Efficient water heaters
 For most of you this picture may not look
like a water heater and you may be wondering why we would use it.
The reason is that your next energy efficient water heater may not be
a conventional boiler at all. Instead it might be what is shown
which is a tankless on demand water heater which heats water
only when you use it. These types of water heaters are designed
to overcome one of the major energy problems with most traditional
water heaters, which is to heat that they waste energy keeping the hot
water at a constant temperature (usually around 140 degrees) even when
it is not being used. This wasted energy can be especially high
if you have an older model water heater which often do not have much
insulation causing energy to be lost rather quickly.
On demand water heaters are extremely popular in Europe but are
just beginning to catch on in the United States. They offer a
number of advantages. First, the energy savings can be significant,
especially in homes where the water demand occurs mainly at night or
in the morning. Energy savings can vary between 20% to as high
as 50%. Second, on demand hot water systems provide the hot
water immediately. No more wasting water while you wait for the cold
water in the pipes to empty out so you can get to the hot water from
the tank. A third advantage is that instant on water heaters can be
dedicated to specific uses to ensure an even steady supply of hot
water. You would no longer have to endure sudden jolts of cold water in the shower just because the washing
machine happened to kick in. A final advantage of an on demand
water heater is that they have a much smaller physical foot print than
a conventional tank water heater. Because there is no need for a
tank the heating elements can be placed in fairly small spaces close
to the source of the water use. This also means that there is
less piping and therefore less heat loss from hot water pipes in your home.
Below is a
picture showing the structure of a typical electric on demand water
heater.  On
demand water heaters come in both electric and gas fired models.
As a general rule the gas on demand water heaters can support a higher
flow rate than electric models. When the hot water tap is turned on, cold
water travels through a pipe into the unit. Then either a gas
burner or an electric element heats the water very rapidly so that it
is available for immediate use.
Another energy efficient option you may wish to consider is using a
solar hot water heater. More than 20% of the energy use in most
homes goes to heating hot water. A solar water heater can
provide much if not all of your hot water needs and can leverage your
existing hot water heating system. Some people believe that
solar water heating only works in warm climates, but in fact, this
approach to water heating can work even in very cold climates.
To find out more about solar hot water heating look in the Energy
Bible solar energy section.
The Energy Star program does not rate tank style hot water heaters.
However, in 2004 the Federal government came out with new energy ratings for hot water heating systems which can be used to
determine which models are most efficient.
The yellow Energy Guide labels on the appliance indicate the Energy Factor (EF), a water heater's overall energy efficiency based on the amount of hot water produced per unit of fuel consumed over a typical day. This includes the following:
- Recovery Efficiency – how efficiently the heat from the energy source is transferred to the water
- Standby Losses – the percentage of heat loss per hour from the stored water compared to the heat content of the water (water heaters with storage tanks)
- Cycling Losses – the loss of heat as the water circulates through a water heater tank, and/or inlet and outlet pipes.
The labels will also provide an estimate of the annual water
heating cost based on the assumption that a typical consumer heats 64
gallons of hot water per day.
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