 | Demand (tankless
or instantaneous) water heaters provide hot water only as it is needed. They
don't produce the standby energy losses associated with storage water
heaters, which can save you money. Here you'll find basic information about
how they work, whether a demand water heater might be right for your home,
and what criteria to use when selecting the right model. |
How They Work:
| Demand water heaters heat water directly without the use of a storage
tank. Therefore, they avoid the standby heat losses associated with storage
water heaters. When a hot water tap is turned on, cold water travels through
a pipe into the unit. Either a gas burner or an electric element heats the
water. As a result, demand water heaters deliver a constant supply of hot
water. You don't need to wait for a storage tank to fill up with enough hot
water. However, a demand water heater's output limits the flow rate. |
| Typically, demand water heaters provide hot water at a rate of 2–5
gallons (7.6–15.2 liters) per minute. Gas-fired demand water heaters produce
higher flow rates than electric ones. Sometimes, however, even the largest,
gas-fired model cannot supply enough hot water for simultaneous, multiple
uses in large households. For example, taking a shower and running the
dishwasher at the same time can stretch a demand water heater to its limit.
To overcome this problem, you can install two or more demand water heaters,
connected in parallel for simultaneous demands of hot water. You can also
install separate demand water heaters for appliances—such as a clothes
washer or dishwater—that use a lot of hot water in your home. |
Other applications for demand water heaters include the following:
| Remote bathrooms or hot tubs |
| Booster for appliances, such as dishwashers or clothes washers
|
| Booster for a solar water heating system. |
Pilot & Ignition considerations:
| Although gas-fired demand water heaters tend to have higher flow rates
than electric ones, they can waste energy if they have a constantly burning
pilot light. This can sometimes offset the elimination of standby energy
losses when compared to a storage water heater. In a gas-fired storage water
heater, the pilot light heats the water in the tank so the energy isn't
wasted. The cost of operating a pilot light in a demand water heater varies
from model to model. Ask the manufacturer how much gas the pilot light uses
for the model you're considering. If you purchase a model that uses a
standing pilot light, you can always turn it off when it's not in use to
save energy. Also consider models that have an intermittent ignition device
(IID) instead of a standing pilot light. This device resembles the spark
ignition device on some gas kitchen ranges and ovens. |
| For homes that use 41 gallons or less of hot water daily, demand water
heaters can be 24%–34% more energy efficient than conventional storage tank
water heaters. They can be 8%–14% more energy efficient for homes that use a
lot of hot water—around 86 gallons per day. You can achieve even greater
energy savings of 27%–50% if you install a demand water heater at each hot
water outlet. |
Selecting a Demand Water Heater:
| Demand water heaters cost more than conventional storage water heaters.
However, you may find that a demand water heater may have lower operating
and energy costs, which could offset its higher purchase price. |
Before buying a demand water heater, you also need to consider the
following:
| Size |
| Fuel type and availability. |
| Energy efficiency (energy factor) |
| Estimate costs. |
Installation and Maintenance:
| Proper installation and maintenance of your demand water heater can
optimize its energy efficiency. |
| Proper installation depends on many factors. These factors include fuel
type, climate, local building code requirements, and safety issues,
especially concerning the combustion of gas-fired water heaters. Therefore,
it's best to have a qualified plumbing and heating contractor install your
demand water heater. |
Do the following when selecting a contractor:
| Request cost estimates in writing |
| Ask for references |
| Check the company with your local Better Business Bureau
|
| See if the company will obtain a local permit if necessary and
understands local building codes, etc. |
| If you're determined to install your water heater yourself, first consult
the manufacturer. Manufacturers usually have the necessary installation and
instruction manuals. Also, contact your city or town for information about
obtaining a permit, if necessary, and about local water heater installation
codes. |
| Most tankless water heaters have a life expectancy of more than 20 years.
They also have easily replaceable parts that extend their life by many more
years. In contrast, storage water heaters last 10–15 years. Periodic water
heater maintenance can significantly extend your water heater's life and
minimize loss of efficiency. Read your owner's manual for specific
maintenance recommendations. |
Improving Energy Efficiency:
| After your demand water heater is properly installed and maintained, try
some additional
energy-saving strategies to help lower your water heating bills. Some
energy-saving devices and systems are more cost-effective to install with
the water heater. |
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