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Is your heating bill in hot water? An on-demand water heater
might help cool things down.
On-demand water heaters, also known as ‘instantaneous’ or
‘tankless’ water heaters, consume on average 30 per cent less
energy than conventional water heaters.
Hot water accounts for 20 per cent or more of an average
household’s annual energy consumption. On-demand heaters can
reduce this by eliminating stand-by heat loss associated with
storage tank water heaters. Instead, when a faucet draws hot
water, the gas burner or electric heating elements turn on,
heating the water in the pipe as needed.
There are some drawbacks to the on-demand option. Units can cost
roughly three times the purchase price of a standard hot water
tank.
Another potential drawback of the average on-demand water heater
is the limited flow rate. This means flow pressure is reduced when
hot water is used simultaneously at different locations. Because
water is heated instantaneously, you’ll never run out of hot
water, even in large homes, with showers one right after the
other. However, a limited flow rate means you can’t run the
dishwasher and take a shower at the same time. There are ways
around this. One is to buy a larger water heater. Another is to
purchase a second water heater and install it in parallel
sequence.
A
third possibility is to choose a gas-fired heater, since these
tend to have greater flow rates than electric ones. However, gas
units are less energy-efficient than electric units. They are
typically only about 80 per cent efficient, while electric units
tend to be close to 95 per cent efficient.
But consumers should also factor in energy costs — based on
current energy costs in Alberta, it costs about 50 per cent less
to operate a natural gas water heater versus an electrical unit.
As with any major appliance, it’s critical to size your unit to
meet the peak demand. On-demand water heaters are sized in gallons
per minute (gpm) of flow. They typically provide two gallons of
hot water per minute. The rate will depend on the difference
between the temperature of water coming into the appliance and the
temperature it is heated to. As a general rule, the greater the
difference in temperature, the lower the flow rate.
To help you size an on-demand heater, here are the average water
flows for various appliances:
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Faucets: 0.75 gallons (2.84 litres) to 2.5 gallons (9.46 litres)
per minute
-
Low-flow shower heads: 1.2 gallons (4.54 litres) to 2 gallons
(7.56 litres) per minute
-
Older standard shower heads: 2.5 gallons (9.46 litres) to 3.5
gallons (13.25 litres) per minute
-
Washing machines and dishwashers: 1 gallon (3.79 litres) to 2
gallons (7.57 litres) per minute
On-demand water heaters may not be for every home. But they can be
a good option for a one-or two-person household, a vacation home,
as a back-up system for a solar water heater, or as a booster
heater for a dishwasher. They can be expected to last a good 20
years without the sediment build-up associated with traditional
storage tank water heaters, which usually last on average 12
years. |
