clear from the bathroom sizing that 1⁄2″ pipe will
also be sufficient for this part of the installation.
The fixture units assigned to a laundry
group (laundry tub and clothes washer) are 1.8
respectively. Therefore, 1⁄2″ pipe will also be
sufficient for these runs.
The short lengths of pipe between the water
heater and the tee that creates separate
branches to the kitchen and laundry room must
carry the combined load for the kitchen and
laundry. The hot water pipe supplies 3.7 fixture
units, and the cold water pipe total is 2.8 fixture
units. In both cases, 1⁄2″ pipe is prescribed by the
reference table.
The cold water pipe from the water heater
to the branch serving hose bibb B carries a
combined load of 14.7 fixture units. The total is
obtained by adding the combined hot and cold
water load for two bathroom groups, a laundry
group, a kitchen group, and a hose bibb. The
table from the model code indicates that 3⁄4″
pipe is required in this location. Changing from
1⁄2″ to 3⁄4″ pipe for this run is warranted because
one branch at the outlet end of this fitting
becomes the hot water piping and the other
branch continues to carry cold water. The cross
sectional area of a 3⁄4″ diameter pipe is approxi-
mately double that of a 1⁄2″ diameter pipe.
Therefore, a sufficient volume of water is avail-
able for both hot and cold water. The 8′ of pipe
from the tee of the branch to hose bibb B to the
water filter, carries a total load of 17.2 fixture
units and also needs to be 3⁄4″ in diameter. The
specifics of sizing water supply piping may be
different for the plumbing code in your area.
You need to become thoroughly familiar with
the requirements of local code to ensure that
your work passes inspection.
Locating Valves and Water
Hammer Arrestors
Before beginning installation, consider
where valves and water hammer arrestors are
needed. Plumbing codes generally require a
valve on the cold water pipe entering the water
heater. Stop and waste valves are required for
hose bibbs that are subject to freezing, unless
frost-proof hose bibbs are installed to extend
through the insulation into heated space. An
individual shut-off valve is required for each
water closet. Valves for water closets are
installed during the finish stage of plumbing
installation. A valve may be installed ahead of
the filter to turn off the water when the filter
cartridge needs to be changed. The water may
also be turned off using the valve installed at
the water supply pipe entry point on the
building. A separate valve ahead of the filter is
primarily a matter of convenience and depends
on the location of the filter, relative to the valve
near the meter.
Code generally requires water hammer
arrestors near quick closing valves. This
includes washing machines and water closets.
The purpose of water hammer arrestors is to
absorb the energy of flowing water when a
valve is closed quickly. This reduces noise in the
piping system and may prevent failure of the
piping system. Many plumbers install air cham-
bers at each stub-out to act as water hammer
arrestors. These air chambers are effective as
long as they do not fill with water. The code
typically does not prohibit the use of air cham-
bers at each stub-out; however, air chambers
may not meet the code requirement for water
hammer arrestors near quick closing valves.
In some cases, valves are installed on major
branches of the piping system to permit just a
portion of the system to be shut off for repairs.
For example, a valve at the beginning of the
branches serving the kitchen and laundry areas
permits continued use of the bathrooms while
repairs are being made in the kitchen or
laundry. Another alternative is to install a valve
at each stub-out so that every fixture is individ-
ually isolated. If installing valves at major
branches, these are installed as the second
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Section 3 Plumbing System Design and Installation
Laundry group: Laundry tub and clothes washer.
Water hammer arrestors: Devices that absorb the
energy of flowing water when a valve is closed
quickly, required by code to be installed near quick
closing valves, such as washing machines and water
closets.