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Automatic
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Energy
Efficient Water Heating
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New
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The next time you pay your utility bill, try one simple calculation.
Divide the total amount by seven. The result is the amount you
spend to heat your water. (If you receive separate utility bills
for gas and electricity, use the gas bill for this calculation
if you have a gas water heater; use the electric bill if you have
an electric water heater.) Of course, you may think this cost
is a small price to pay for the convenience of a hot shower. But
during the course of a year, this cost adds up. And when you consider
that 95 million households in this country pay the same percentage,
it is easy to see how much money--and energy--is used to heat
water.
Several measures can help you decrease water-heating costs in
your home. Some specific actions include reducing the amount of
hot water used, making your water-heating system more energy efficient,
and using off-peak power to heat water.
Reducing the Amount of Hot Water Used
Generally, four destination points in the home are recognized
as end uses for hot water: faucets, showers, dishwashers, and
washing machines. Now, you do not have to take cold showers, dine
on dirty dishes, or wear dirty clothes to reduce your hot-water
consumption. Less radical measures are available that will be
virtually unnoticeable once you apply them.
Faucets and Showers
Simply repairing leaks in faucets and showers can save hot water.
A leak of one drip per second can cost $1 per month, yet could
be repaired in a few minutes for less than that. And some apparently
insignificant steps, when practiced routinely at your household,
could have significant results. For example, turning the hot-water
faucet off while shaving or brushing your teeth, as opposed to
letting the water run, can also reduce water-heating costs. Another
option is limiting the amount of time you spend in the shower.
Other actions may require a small investment of time and money.
Installing low-flow showerheads and faucet aerators can save significant
amounts of hot water. Low-flow showerheads can reduce hot-water
consumption for bathing by 30%, yet still provide a strong, invigorating
spray. Faucet aerators, when applied in commercial and multifamily
buildings where water is constantly circulated, can also reduce
water-heating energy consumption.
Older showerheads deliver 4 to 5 gallons (15.1 to 18.9 liters)
of water per minute. However, the Energy Policy Act of 1992 sets
maximum water flow rates at 2.5 gallons (9.5 liters) per minute
at a standard residential water pressure of 80 pounds per square
inch (552 kilopascals).
A quick test can help you determine if your shower is a good
candidate for a showerhead replacement. Turn on the shower to
the normal pressure you use, hold a bucket that has been marked
in gallon increments under the spray, and time how many seconds
it takes to fill the bucket to the 1-gallon (3.8-liter) mark.
If it takes less than 20 seconds, you could benefit from a low-flow
showerhead. A top-quality, low-flow showerhead will cost $10 to
$20 and pay for itself in energy saved within 4 months. Lower
quality showerheads may simply restrict water flow, which often
results in poor performance.
Because of the different Uses of bathroom and kitchen faucets,
you may need to have different water flow rates in each location.
For bathroom faucets, aerators that deliver 0.5 to 1 gallon (1.9
to 3.8 liters) of water per minute may be sufficient. Kitchen
faucets may require a higher flow rate of 2 to 4 gallons (7.6
to 15.1 liters) per minute if you regularly fill the sink for
washing dishes. On the other hand, if you tend to let the water
run when washing dishes, the lower flow rate of 0.5 to 1 gallon
per minute may be more appropriate. Some aerators come with shut-off
valves that allow you to stop the flow of water without affecting
the temperature.
Automatic Dishwashers
A relatively common assumption is that washing dishes by hand
saves hot water. However, washing dishes by hand several times
a day could be more expensive than operating some automatic dishwashers.
If properly used, an efficient dishwasher can consume less energy
than washing dishes by hand, particularly when you only operate
the dishwasher with full loads.
The biggest cost of operating a dishwasher comes from the energy
required to heat the water before it ever makes it to the machine.
Heating water for an automatic dishwasher can represent about
80% of the energy required to run this appliance.
Average dishwashers use 8 to 14 gallons (30.3 to 53 liters) of
water for a complete wash cycle and require a water temperature
of 140 degrees F (60 degrees C) for optimum cleaning. But setting
your water heater so high could result in excessive standby heat
loss. This type of heat loss occurs because water is constantly
heated in the storage tank, even when no hot water is used. Furthermore,
a water heater temperature of 120 degrees F (48.9 degrees C) is
sufficient for other uses of hot water in the home.
The question, then, is must you give up effective cleaning for
hot-water energy savings? The answer is no. A "booster"
heater can increase the temperature of the water entering the
dishwasher to the 140 degrees F recommended for cleaning. Some
dishwashers have built-in boosters that will automatically raise
the water temperature, while others require manual selection before
the wash cycle begins. A booster heater can add about $30 to the
cost of a new dishwasher but should pay for itself in water-heating
energy savings in about 1 year if you also lower your water heater
temperature. Reducing the water heater temperature is not advisable,
however, if your dishwasher does not have a booster heater.
Another feature that reduces hot-water use in dishwashers is
the availability of cycle selections. Shorter cycles require less
water, thereby reducing the energy cost. The most efficient dishwasher
currently on the market can cost half as much to operate as the
most inefficient model. If you are planning to purchase a new
dishwasher, check the EnergyGuide labels and compare the approximate
yearly energy costs among brands. Dishwashers fall into one of
two categories: compact capacity or standard capacity. Although
compact-capacity dishwashers may appear to be more energy efficient,
they hold fewer dishes and may force you to use the appliance
more frequently than you would use a standard-capacity model.
In this case, your energy costs could be higher than with the
standard-capacity dishwasher.
Washing Machines
Like dishwashers, much of the cost--up to 90%--of operating washing
machines is associated with the energy needed to heat the water.
Unlike dishwashers, washing machines do not require a minimum
temperature for optimum cleaning. Either cold or warm water can
be used for washing most laundry loads; cold water is always sufficient
for rinsing. Make sure you follow the cold-water washing instructions
for your particular laundry detergent. Washing only full loads
is another good rule of thumb for reducing hot-water consumption
in clothes washers.
As you would for dishwashers, consult the Energy Guide labels
when shopping for a new washing machine. Inefficient washing machines
can cost three times as much to operate as efficient machines.
Select a machine that allows you to adjust the water temperature
and water levels for the size of the load. Also, front-loading
machines use less water and, consequently, less energy than top
loaders. However, in this country, front loaders are not as widely
available as top loaders. Keep in mind that the capacity of front
loaders may be smaller than that of most top-loading machines.
Smaller capacity washing machines often have better Energy Guide
ratings. However, a reduced capacity might cause you to increase
the number of loads you wash and possibly increase your energy
costs.
Faucets, showerheads, dishwashers, and washing machines are only
destination points for hot water in your home. The journey of
your hot water before it reaches these outlets can be fraught
with opportunities for energy losses. Fortunately, you can reduce
the incidence of water heat loss from the point of departure to
the point of arrival by applying a few basic measures.
Increasing Water-Heating System Efficiency
Reducing hot-water usage is primarily a matter of common sense
and exerting a little extra effort to not be wasteful. Once you
have applied a few simple, low-cost measures for reducing hot-water
consumption, you may want to consider water-heating system improvements
if you wish to further reduce your energy bill.
Lower Your Water Heater Thermostat
One simple step for reducing water-heating energy costs is lowering
the thermostat setting on your water heater. Although some manufacturers
set water heaters at 140 degrees F (60 degrees C), 120 degrees
F (48.9 degrees C) is satisfactory for most household needs. Furthermore,
when heated to 140 degrees F, water can pose a safety hazard (i.e.,
scalding). For each 10 degrees F (5.6 degrees C) reduction in
water temperature, water-heating energy consumption can be reduced
3% to 5%.
If your dishwasher does not have a booster heater, lowering the
water-heating temperature is not recommended. Also, many dishwasher
detergents are formulated to clean effectively at 140 degrees
F and may not perform adequately at lower temperatures. (See previous
discussion on Automatic Dishwashers.)
On gas water heaters, thermostats are usually visible. Electric
water heaters, on the other hand, may have thermostats positioned
behind screw-on plates. As a safety precaution, shut off electric
current to the water heater before removing the plates. Keep in
mind that electric water heaters may have two thermostats to adjust--one
each for the upper and lower heating elements--and adjusting these
is tricky. Talk to your local water-heating professional for help
with this.
When you plan to be away from home for an extended period of
time (at least 3 days), turning the water heater thermostat down
to the lowest setting, or even turning the heater off completely,
can help you achieve additional savings. Be sure you know how
to relight the pilot light on your gas heater, though, before
you turn it off.
Insulate Hot-Water Pipes and the Storage Tank
When you turn on a hot-water faucet during cold weather, it may
take several seconds for the water to become hot. This happens
because the water travels through pipes from the water heater
to the faucet, and some of the pipes may pass through unheated
sections of the house, such as the basement. As a result, the
hot water loses some of its heat to the surrounding space.
This heat loss can be reduced by insulating hot water pipes wherever
they are accessible--especially in unheated areas. Use quality
pipe insulation wrap, or neatly tape strips of fiberglass insulation
around the pipes. Eventually the water will cool, but it will
remain warmer much longer inside insulated pipes.
Insulating your water-heater storage tank is a fairly simple
and inexpensive improvement that can help maintain the water temperature
at the thermostat setting. Some newer models of water heaters
are well insulated and do not need an added layer, but a heater
that is warm to the touch needs additional insulation.
Easy-to-install, pre-cut blankets (or jackets) for electric water
heaters are widely available and range in cost from $10 to $20.
Your local utility company may offer them at a lower price, give
you a rebate, or even install them at no cost. When properly installed,
a water heater blanket on an electric water heater will pay for
itself in energy saved within 1 year. Installation is more difficult
on gas- and oil-fired heaters. Ask your local furnace installer
for instructions.
If your water heater is at least 7 years old, you should carefully
evaluate your water-heating needs and investigate the types of
heaters that could replace your current one. Although most water
heaters last 10 to 15 years, early investigation and timely replacement
can ensure a wiser purchase. For more information on the types
of water heaters now available, contact the Energy Efficiency
and Renewable Energy Clearinghouse (EREC--see Source List).
Using Off-Peak Power to Heat Water
Most consumers use more hot water in the evenings and mornings
than at other times of the day. For those who have an electric
water heater, this usage contributes to the electric utility company's
"peak load," or the largest amount of power demand that
they have to meet on a daily basis. Some utilities are required
to offer their customers "time of use" rates that vary
according to the demand on their system. Lower rates may be charged
at "off-peak" times and higher rates at "on-peak"
times. You may be able to lower your electric bills if you can
take advantage of these rate schedules. Check with your local
electric utility to find out if it offers time-of-use rates for
residential customers, and if so, what the rate schedules are.
Some utilities even offer incentives for customers who allow their
utility to install control devices that shut off electric water
heaters during peak demand periods.
Simple Actions, Big Results
Some ways to save on water-heating bills require greater financial
investments than others. You may wish to consider the no- or low-cost
options before making large purchases. Also allow for circumstances
that may be unique to your household when deciding on the appropriate
options (e.g., a small-capacity washing machine could meet the
needs of a one-person household efficiently).
Although it is not feasible to eliminate water heating in your
home, it is possible to substantially reduce water-heating costs
without sacrificing comfort and convenience. The tips in this
publication can help decrease your costs for heating water.
Installing an Insulation Blanket on an Electric Water Heater
Note: Installation is more difficult on gas- and oil-fired heaters.
Ask your local furnace installer for instructions.
- Cut the tank top insulation to fit around the piping in the
top of the tank. Tape the cut section closed after the top has
been installed.
- Fold the corners of the tank top insulation down and tape
to the sides of the tank (Figure 1).
- Position the insulating blanket around the circumference of
the tank. For ease of installation, position the blanket so
that the ends do not come together over the access panels in
the side of the tank. Some tanks have only one access panel.
- Secure the blanket in place with the belts provided. Position
the belts so they do not go over the access panels (Figure 2).
Belts should fit snugly over the blanket but not compress it
more than 15% to 20% of its thickness. The installation is easier
with two people. If working alone, use tape to hold the blanket
to the top until you get the belts into position.
- If your water heater has the temperature/pressure relief valve
and the overflow pipe on the side of the tank instead of on
the top, install the blanket so these items are outside of the
blanket. Depending on the piping arrangement and location, you
may need to compress, or even cut, the blanket.
- Locate the four corners of the access panel(s). Make an x-shaped
cut in the insulating blanket from corner to corner of each
access panel (Figure 3).
- Fold the triangular flaps produced by the cuts underneath
the insulating blanket (Figure 4). Repeat steps 6 and 7 for
the rating/instruction plate.
- The blanket must not be installed on a leaking tank.
Source List
The following organizations and publications provide more information
on hot-water energy efficiency. Much of the information included
in this publication was obtained from several of these sources.
This list does not cover all the available books, reports, and
articles on hot-water energy efficiency, nor is the mention of
any publication to be considered a recommendation or endorsement.
To obtain the publications in this list, contact your local library
or bookstore or the publisher. Check publication prices through
your bookstore or the publisher before placing an order.
- American Council for an Energy-Efficient Economy (ACEEE) 1001
Connecticut Avenue, NW, Suite 801 Washington, DC 20036 (202)
429-8873 or 2140 Shattuck Avenue, Suite 202 Berkeley, CA 94704
- ACEEE provides general and technical information on energy
efficiency, including these publications: The Consumer Guide
to Home Energy Savings, The Most Energy-Efficient Appliances,
and Saving Energy and Money with Home Appliances. These publications
can be ordered by writing the ACEEE office in Berkeley, California.
- Association of Home Appliance Manufacturers (AHAM) Information
Center 20 North Wacker Drive Chicago, IL 60606 (312) 984-5800
ext. 315
- AHAM provides energy efficiency information for specific brands
of major appliances. The association also runs a certification
program for certain types of appliances.
- Gas Appliance Manufacturers Association, Inc. (GAMA) 1901
North Moore Street, Suite 1100 Arlington, VA 22209 (703) 525-9565
- GAMA has information on residential gas appliances and equipment,
electric and oil-fired water heaters, and oil-fired warm air
furnaces.
- U.S. Department of Energy Energy Information Administration
(EIA) National Energy Information Center EI-231, Room 1F-048
Forrestal Building Washington, DC 20585 (202) 586-8800
- EIA compiles a wide range of statistics for the energy professional
on energy sources and energy consumption. EIA s Household Energy
and Consumption and Expenditures contains information on residential
energy use.
Further information about efficient water heating can be obtained
by contacting:
- The Energy Efficiency and Renewable Energy Clearinghouse (EREC)
P.O. Box 3048 Merrifield, VA 22116 (800) 363-3732
- EREC provides free general and technical information to the
public on a wide spectrum of topics and technologies pertaining
to energy efficiency and renewable energy.
- Also contact your state and local government energy offices
and utility for additional information on energy-efficient water
heaters, installation, and rebate or incentive programs.
Reading List
- Books and Reports Consumer Reports 1992 Buying Guide Issue,
Consumers Union of the United States, Inc., 101 Truman Avenue,
Yonkers, NY 10703-1057, December 1991.
- The Water Heater Workbook: A Hands-on Guide to Water Heaters,
published by Elemental Enterprises, P.O. Box 928, Monterey,
CA 93942, 1992.
- "Water Heating," Energy Edge, Pennsylvania Energy
Office, 116 Pine Street, Harrisburg, PA 17101 (printed by DOE).
Articles
- "An Investigation of Off-Peak Domestic Hot Water Heating,"
ASHRAE Journal, p. 32, January 1990.
- "Dishwashers," Consumer Reports, p. 637, October
1993.
- "Hot Water Energy Conservation: Heating Water Accounts
for 15% to 25% of an Average Family s Energy Budget," Consumer
s Research Magazine, p. 19, January 1991.
- "Safer Water Filters, Cheaper Water-Heating Systems,
and More," Home Mechanix, p. 37, June 1993.
- "Showering Them With Gas," American Gas, p. 22,
April 1989.
This document was produced for the U.S. Department of Energy
(DOE) by the National Renewable Energy Laboratory (NREL), a DOE
national laboratory. The document was produced by the Information
Services Program, under the DOE Office of Energy Efficiency and
Renewable Energy. The Energy Efficiency and Renewable Energy Clearinghouse
(EREC) is operated by NCI Information Systems, Inc., for NREL/DOE.
The statements contained herein are based on information known
to EREC and NREL at the time of printing. No recommendation or
endorsement of any product or service is implied if mentioned
by EREC.
DOE/GO-10095-063 FS 204 January 1995
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