Handbook

3. DESIGN AND INSTALLATION DATA
Pressure System Sizing
Designing a copper tube water supply system is
a matter of determining the minimum tube size
for each part of the total system by balancing
the interrelationships of six primary design
considerations:
1. Available main pressure;
2. Pressure required at individual xtures;
3. Static pressure losses due to height;
4. Water demand (gallons pter minute) in the total
system and in each of its parts;
5. Pressure losses due to the friction of water ow
in the system;
6. Velocity limitations based on noise and erosion.
Design and sizing must always conform to applicable
codes. In the nal analysis, design must also reect
judgment and results of engineering calculations.
Many codes, especially the model codes, include
design data and guidelines for sizing water
distribution systems and also include examples
showing how the data and guidelines are applied.
Small Systems
Distribution systems for single-family houses can
usually be sized easily on the basis of experience
and applicable code requirements, as can other
similar small installations. Detailed study of the six
design considerations above is not necessary in
such cases.
In general, the mains that serve xture branches can
be sized as follows:
 Up to three 3/8-inch branches can be served by
a 1/2-inch main.
 Up to three 1/2-inch branches can be served by
a 3/4-inch main.
 Up to three 3/4-inch branches can be served by
a 1-inch main.
The sizing of more complex distribution systems
requires detailed analysis of each of the sizing design
considerations listed above.
Pressure Considerations
At each xture in the distribution system, a minimum
pressure of 8 psi should be available for it to function
properly - except that some xtures require a higher
minimum pressure for proper function, for example:
 Flush valve for blow-out and syphon-jet closets
- 25 psi
 Flush valves for water closets and urinals
- 15 psi
 Sill cocks, hose bibbs and wall hydrants
- 10 psi
Local codes and practices may be somewhat
dierent from the above and should always be
consulted for minimum pressure requirements.
The maximum water pressure available to supply
each xture depends on the water service pressure
at the point where the building distribution system
(or a segment or zone of it) begins. This pressure
depends either on local main pressure, limits set
by local codes, pressure desired by the system
designer, or on a combination of these. In any case,
it should not be higher than about 80 psi (pounds per
square inch).
However, the entire water service pressure is not
available at each xture due to pressure losses
inherent to the system. The pressure losses include
losses in ow through the water meter, static losses
in lifting water to higher elevations in the system, and
friction losses encountered in ow through piping,
ttings, valves and equipment.
Some of the service pressure is lost immediately
in ow through the water meter, if there is one. The
amount of loss depends on the relationship between
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CDA Publication A4015-14/20: Copper Tube Handbook
3. DESIGN DATA