PEX Installation Manual

IM-PF 724596 0416
20
9.2 Combination systems
PEX combination systems can be sized in a similar
manner as a typical branch-and-tee system.
Refer to your local or model plumbing code for
the required tube and manifold sizing based on
the system demand (Water Service Fixture Units,
WSFU). If low service pressure is present, Viega
provides the equivalent feet of PEX tubing factors
for PEX ttings to ensure any additional pressure
drop is accounted for in your design.
9.3 Branch-and-tee systems
The same general sizing practices can be applied
to a PEX branch-and-tee system as with any code-
approved piping material. Refer to your local or
model plumbing code for proper tube sizing.
Design factors for installing combination systems
Design the layout as condensed as possible
Keep the main hot supply line close to the fixture
groups with the branch lines shorter than six feet.
This will help provide hot water in a reasonable
amount of time with less wasted water.
The limiting factor for installers to accomplish an
optimal design is how spread out the fixture groups
are within the structure.
If there is a floor plan that incorporates stacked or
back-to-back fixture groups, a combination system
can be an effective alternative to a parallel system.
Design factors for installing branch-and-main
systems
Just like the combination system, condensed floor
plan layouts are preferable to minimize the length and
the amount of water stored in the main supply line,
minimizing the amount of water purged before hot
water reaches the fixtures. These systems can also
suffer from fluctuating pressure during multiple fixture
use.
If the fixture groups are not condensed, a branch-and-
main system will have slow hot water delivery times
and substantial water waste.