Energy Efficient Homes: Water Heaters1 - UF/IFAS Edis

Energy Efficient Homes: Water Heaters1
Wendell A. Porter, Kathleen C. Ruppert, and Randall A. Cantrell2
Quick Facts
• Water heating is often the third largest energy expense in
your home, after heating and cooling—it can account for
13%–17% of your utility bill.
• The optimum temperature for both energy efficiency and
function is 120°F. Higher temperatures increase energy
costs and scalding risks. Note: most electric water heaters
have two thermostats (one for each heating element), and
it is important to make sure they are both at the same
setting. For each 10°F reduction in water temperature,
you can save 3%–5% in energy costs.
• Install an Energy Star clothes washer. Most of the energy
consumed when washing clothes is used to heat the water.
• Install an Energy Star dishwasher; as with clothes washers, most of the energy consumed by dishwashers is used
to heat the water.
• Check with your utility company as it may offer rebates
or incentives for certain types of energy-efficient water
heaters. Keep in mind that your choice of water heater
and its fuel source will depend, in part, on where you live
and the space available.
• Install heat traps, one-way valves or loops of pipe, which
prevent heated water in a storage tank from mixing with
cooled water in pipes. Most new water heater models
have factory-installed heat traps. Heat traps can save you
$15–$30 per year by preventing convective heat losses
through the inlet and outlet pipes.
• If you have a tank-style water heater, drain about a quart
of water from the water tank every 3–6 months. This
helps to remove sediment that slows down heat transfer
and lowers the efficiency of your water heater. Follow the
manufacturer’s recommendations for your specific unit.
• If your water heater is more than 10 years old, it is a good
idea to start shopping for a new one now. This will give
you a chance to do some research and select the type
and model that most appropriately meets your needs.
Although most water heaters last 10–15 years, it might be
economically smarter to replace your water heater early;
the lower utility bills could be worth it. Compare costs:
purchase price and lifetime maintenance and operation
• For safety concerns as well as energy efficiency reasons,
when buying fuel-fired water heaters, look for units
with sealed combustion or power venting to avoid back
drafting of combustion gases into your home. If fuel-fired
water heaters are located in interior spaces, such as
interior mechanical rooms connected to conditioned
spaces or laundry rooms, they should include provisions
for outside combustion air. Also, install a hardwired
carbon monoxide alarm (with battery backup) nearby.
1. This document is FCS3277, one of an Energy Efficient Homes series of the Family, Youth and Community Sciences Department, UF/IFAS Extension.
This material was prepared with the support of the Department of Environmental Protection, Florida Energy Office. However, any opinions, findings,
conclusions, or recommendations expressed herein are those of the author(s) and do not necessarily reflect the views of the Florida Department of
Environmental Protection. Original publication date June 2008. Revised February 2015. Visit the EDIS website at
2. Wendell A. Porter, PhD, PE and lecturer, Department of Agricultural and Biological Engineering; Kathleen C. Ruppert, EdD, UF/IFAS Extension scientist,
Program for Resource Efficient Communities; and Randall A. Cantrell, PhD, assistant professor, Department of Family, Youth, and Community Sciences;
UF/IFAS Extension, Gainesville, FL 32611.
The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services
only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status,
national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county’s UF/IFAS Extension office.
U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County
Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.
Terms to Help You Get Started
Energy Factor (EF)—the ratio of energy received from
the water heater to the total amount of energy delivered to
the water heater; the higher the better; determined by U.S.
Department of Energy test procedures.
Energy Star Qualifying Products—Residential waterheater product classes that are eligible for Energy Star as
of April 16, 2015: storage, instantaneous (“tankless”), solar
water, and light duty (see
cfm?c=water_heat.pr_crit_water_heaters for details).
First-Hour Rating (FHR)—The amount of hot water in
gallons a storage water heater can supply per hour (starting
with a full tank of hot water); determined by the manufacturer using U.S. Department of Energy procedures.
Gallons Per Minute (GPM)—The amount of hot water
in gallons a tankless water heater can supply per minute
during a 77°F temperature increase; determined by the
manufacturer using U.S. Department of Energy procedures.
Solar Energy Factor (SEF)—replaces the earlier term “Solar
Fraction (SF)”—Both terms mean the same thing. The
amount of energy provided by the solar technology divided
by the total energy put into the system; used in determining
the efficiency of solar water heaters.
What Do You Need to Know?
No matter how you heat water for your home, be certain to
take advantage of the savings from these easy conservation
• Install shutoff valves on low-flow showerheads and
kitchen faucets. Designed to dribble when closed, the
valve controls flow at the push of a button so that water in
the pipe stays at the selected temperature while soaping,
shaving, or shampooing. These valves are a built-in
feature of many low-flow heads.
• Include low-flow aerators or laminar-flow controls on
sink and lavatory faucets.
• Install low-flow showerheads with well-designed features
that deliver water at about 1.5–2.5 gallons per minute
while still providing plenty of force.
• Insulate. Wrap the outside of your water-heater tank with
an insulation jacket (sometimes called a water-heater
blanket). This is especially useful for older water heaters; new water heaters are often well insulated already.
Insulate the first 3 to 4 feet of the cold and hot water pipes
connected to the unit. Be sure to follow manufacturer’s
Energy Efficient Homes: Water Heaters
directions for installation of any kind of insulation.
Caution should be taken if insulating a natural gas or
propane fired water heater. The insulating blanket can
inadvertently block the air intake causing a health and
fire hazard.
• If you have a system with a long distance between the
water heater and a major hot water demand area, such
as a master bathroom at one end of your house and the
water heater at the other end, then you may want to
consider a hot water recirculation system. These systems
reduce the amount of water that goes down the drain
while you wait for the desired temperature.
• Schedule regular maintenance and performance checks.
Refer to the manufacturer’s manual for your model before
attempting any maintenance procedure.
What Should You Consider When
Purchasing a New Water Heater?
You need a water heater capable of providing adequate
amounts of hot water during your household’s busiest
times of the day. For help in determining your family’s
peak-hour demand for hot water, see the Consumer’s Guide
to Energy Efficiency and Renewable Energy at http://www.
mytopic=12990. In selecting a tank-style water heater,
look for one with a first hour rating (FHR) that matches
within 1 to 2 gallons of your peak-hour demand. The FHR
is a measure of how much hot water the heater will deliver
during a busy hour. Federal law requires this information to
be on the unit’s EnergyGuide label.
For new construction, minimize piping runs to hot water
requiring areas of the home by design or by centrally
locating the water heater. Insulate buried hot-water piping
for new construction to minimize heat loss while hot water
is flowing through or remaining stagnant in the pipes.
Leave the pipe 6 inches below and 6 inches above the slab
free of insulation, as having insulation through the slab may
increase the potential for insect problems. Insulate all hot
water lines in interior walls. Also, insulate all water lines in
attic or floor joists.
Choose an Energy Star–labeled water heater. The new
criteria go into effect on April 16, 2015. Go to http:// to see the new requirements and choose a water
heater that meets the Energy Star criteria.
What Are Your Choices for Water
One of the first steps in choosing a water heater is to
determine the appropriate fuel type. The fuel type or energy
source you use not only affects the water heater’s annual
operating cost, but also its size and energy efficiency. If
considering changing fuel sources, check with your utility
company as it may offer rebates or incentives for switching
to a gas- or solar-powered water heater. Your choice of
water heater and its fuel source will depend, in part, on
what area of the state you live in.
Storage water heaters are the most common type. Water
is heated in an insulated tank. When the hot-water tap
is turned on, hot water flows out of the top of the water
heater, and cold water flows into the bottom of the tank to
replace the hot water in the top of the tank.
Heat-pump water heaters use electricity for moving heat
from one place to another rather than generating heat
directly. Refrigerants and compressors transfer heat from
the surrounding air into an insulated storage tank.
Demand (tankless or instantaneous) water heaters heat
water directly without use of a storage tank. A gas burner or
electric element heats water only when there is a demand.
Note: There has been some concern expressed about using
these units in areas with “hard” water (calcium carbonate
rich). Be sure to check with the manufacturer if this is a
potential problem.
Tankless-coil water heaters use the home’s main heating
system to heat the water. They operate off the house boiler
with no separate storage tank.
Indirect water heaters use the home’s heating system as
the heat source, but the water from the boiler is circulated
through a heat exchanger in a separate, insulated tank.
Because hot water is stored in a tank, the boiler does not
have to turn on and off as often.
Solar water heaters use the sun’s thermal energy to heat
water. These units are usually designed to serve as preheaters for conventional storage or tankless water heaters.
A solar collector absorbs thermal energy from the sun
and transfers this heat to water in a storage tank or water
entering a tankless water heater. Note that all solar energy
systems manufactured or sold in Florida must meet the
standards established by the Florida Solar Energy Center
and display accepted results of approval performance tests.
See Florida law (section 377.705, Florida Statutes) and
Energy Efficient Homes: Water Heaters for more information. Also, see the
Solar Rating and Certification Corporation (SRCC) website
at SRCC is a non-profit
organization whose primary purpose is the development
and implementation of certification programs and national
rating standards for solar energy equipment.
Drain-Water Heat Recovery—sometimes referred to as
heat recovery units (HRU) or grey water recovery units—
systems operate with all types of water heaters, especially
demand and solar types. In essence, the system “captures”
some of the heat from hot water traveling through the pipe
as it goes down the drain. The system then uses this heat
to pre-heat the incoming cold water that goes to the water
heater or a fixture, such as a shower.
Gas-condensing water heaters are similar to conventional
gas storage water heaters with a few exceptions. The major
enhancement these units have over the conventional units
is the ability to capture the heat of condensation of the
combustion gases. The burner heats the water like typical
gas storage models, but the combustion gases are vented
through coils that provide additional heat to the water.
Residential gas-condensing water heaters are popular in Europe, but they are mostly found in commercial applications
in North America. However, manufacturers are considering
developing this product line if a market is available.
In addition to considering the water heater types available
to you and determining the size system you will need, you
will also want it to perform efficiently. Luckily, there are
indicators that will help you do just that.
Energy Factor
The best indicator of a heater’s efficiency is its Energy Factor
(EF). EF is based on recovery efficiency (i.e., how efficiently
the heat from the energy source is transferred to the water);
standby losses (i.e., the percentage of heat lost per hour
from the stored water compared to the heat content of the
water); and cycling losses, based on an average household
use of 64 gallons of hot water per day. The higher the EF,
the more efficient the water heater.
EnergyGuide Label
Look at the bright yellow and black EnergyGuide label
to indicate the estimated annual energy consumption
and operating cost of the water heater (given at a certain
rate). The EnergyGuide label is found on certain types of
storage, instantaneous, and heat-pump type water heaters.
The label provides estimated annual energy consumption
of a particular model on a scale showing its performance
compared to a range of similar models. By comparing a
model’s annual operating cost with the operating cost of the
most efficient model, you can compare efficiencies.
Home Innovation Research Labs. Hot Water Recirculation
Systems. Accessed September 23, 2014.
If considering electric or gas-storage water heaters, use
the U.S. Department of Energy’s interactive Energy Cost
Calculator for Electric and Gas Water Heaters at http:// to help you make your decision.
Home Innovation Research Labs. Solar Water Heaters.
Accessed September 23, 2014.
No matter what type of water heater you look at, be sure to
compare warranties—including those portions applicable to
labor and parts—along with the maintenance requirements
of the unit.
References and Resources
Air Conditioning, Heating, and Refrigeration Institute
(AHRI). Directory of Certified Product Performance.
Accessed January 12, 2015.
ahridirectory/pages/home.aspx. *Search this database—
under the Residential list, click on Water Heaters--to find
available products by energy factor and tank size. Make sure
you specify your energy source, gas type, and heater type
before conducting the search.
American Council for an Energy-Efficient Economy. Water
Heating. Accessed January 12, 2015.
California Urban Water Conservation Council. H2Ohouse
Water Saver Home. Accessed September 23, 2014. http://
Coalition for Energy Star Water Heaters. Accessed January
12, 2015.
Florida Building Code. – especially requirements for fuel-fired appliances, such as water
heaters and furnaces. In particular, “Chapter 7: Combustion
Air” of Florida Building Code, Mechanical. Accessed September 23, 2014.
aspx (Requires JavaScript).
Florida Solar Energy Center. Accessed September 23, 2014.
Home Innovation Research Labs. Heat Pump Water Heaters. Accessed September 23, 2014.
Energy Efficient Homes: Water Heaters
Home Innovation Research Labs. Tankless Water Heaters.
Accessed September 23, 2014.
Hot Water Heaters Reviews. Accessed September 23, 2014.
Solar Rating and Certification Corporation. Accessed
September 23, 2014.
Southface Energy Institute. Accessed September 23, 2014.
U.S. Department of Energy. Energy Saver$ Tips on Saving Energy & Money at Home. Accessed September 23,
U.S. Department of Energy. Water Heating. Accessed
September 23, 2014.
U.S. Environmental Protection Agency. WaterSense.
Accessed September 23, 2014.
U.S. Environmental Protection Agency. Energy Star Product
Specification for Residential Water Heaters. Accessed
January 12, 2015.
U.S. Environmnetal Protection Agency. Residential Water
Heaters Key Product Criteria. Accessed January 12, 2015.
U.S. Government. Electronic Code of Federal Regulations.
Accessed January 12, 2015.