Optional Water Efficiency Measure: May contribute to the 30 percent water efficiency requirement,
depending on the chosen WaterSense® Approved Certification Method (WACM).

UNDERSTAND
Efficient hot water delivery (HWD) systems provide hot water to fixtures faster, wasting less time, water,
energy, and money.
To design efficient HWD systems, minimize pipe run lengths and right-size pipe diameters.
Residential HWD systems come in a variety of design installation methods and materials. Some of the
most common are summarized in the table below.
HWD System Description
Trunk-and-branch systems have one or more
long, large diameter common flow main lines
(trunks) that run from the water heater to the
farthest fixture. "Branches" from the main trunk
supply hot water to different parts of the house,
and "twigs" provide hot water to individual
fixtures.
HWD System Schematic
Fixture Fixture
Fixture
Hot Water Heater
E
E
S Fixture
Fixture
Fixture
Core systems rely on a centrally located water
heater that can supply fixtures with individual
small-diameter pipes.
Fixture
Fixture
Hot Water Heater
Fixture
Fixture
Fixture
Whole-house manifold systems supply a
central manifold with a single, short, large-
diameter pipe and have small-diameter piping
running from the manifold to reach individual
fixtures.
Fixture	Fixture
Fixture Fixture
Manifold —
Fixture Fixture
— Hot Water Heater
Recirculation systems have a continuous loop
of hot water recirculating through the home by
means of a circulating pump. Ensuring the
recirculation is demand-activated (for example
by a push button or motion sensor) ensures
that recirculation does not unnecessarily
increase the energy used to heat water.
Fixture Fixture Fixture Fixture
Hot Water
Heater
Check Circulating
Valve Pump

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BUILD
•	DESIGN a hot water distribution system that meets the needs
of the homeowner and achieves performance by considering
the layout of the home and the most appropriate type of
piping for the system.
•	AIM to design and install a system that has the lowest volume
of water between the water heater and each end use
possible. A good target is 0.5 gallons or less between each
end use (e.g., shower, faucet).
•	COORDINATE verification of the HWD system by a
WaterSense home verifier, if possible, prior to installation of
drywall.
VERIFY
•	VERIFY the volume and time needed to detect a 10°F
temperature change by identifying the fixture farthest from
the hot water source. Place a bucket under the hot water
fixture, turn the hot water completely on, and use a
thermometer to record the starting temperature. Once the
water temperature has increased by 10°F, turn off the water.
Measure and record the volume of water collected.
•	CONFIRM that a demand-initiated recirculation pump has
been installed, if applicable.
*NOTE: Consult with the Home Certification Organization (HCO) for
specific verification protocols.
Energy-Saving Heat Pumps
Water heaters use about 20
percent of a home's energy.
Builders can install an
ENERGY STAR0 certified
heat pump water heater to
help reduce energy use
associated with heating
water. Visit the ENERGY
STAR Super-Efficient Water
Heater web page at
www.energystar.gov/produc
ts/energy star home upgra
de/super efficient water he
aterto learn more and find
eligible models.
Piping Materials
There are several choices for pipe
materials, although their selection may
be influenced by the type of system
being installed:
•	Trunk-and-branch and core
systems traditionally use copper
pipes but can use any type of
piping.
•	Whole-house manifold systems
use flexible piping, such as types
of cross-lined polyethylene (PEX).
•	Demand-initiated recirculation
systems can use any type of
piping.
Consider the effect of pipe diameter on
efficiency and performance of the
system. For example, smaller diameter
piping may be acceptable to deliver
water from the main supply line to
individual fixtures, whereas the main
line requires larger diameter piping to
ensure adequate flow.
Pipe insulation can further improve
HWD efficiency, as it reduces the
overall rate of heat loss from water
stored in the piping. Pipe insulation
with a minimum R value of R-3 should
be used.
Learn More
Check out WaterSense's Guide for
Efficient Hot Water Delivery Systems at
www.epa.gov/watersense/watersense-
labeled-homes-hot-waterto learn
about designing hot water delivery
systems to reduce wait times and
maximize water efficiency.
This technical fact sheet is part of EPA's Technical Reference Manual for
WaterSense Labeled Homes. For the full document and other tools and	EPA-832-F-23-016
resources for homes, visit www.epa.gov/waterserise/tools-and-resources.	July 2023

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