
Parker Hannifin Corporation
Parflex Division
Ravenna, Ohio
Bulletin No. 4660-PGP2T
Parflex
®
Flexible Gas Piping System
Design and Installation Guide
Section 3.0 System Configuration & Sizing
3.2.5
Parallel Elevated System Example
Elevated Parallel
This example shows a rooftop application to six
HVAC Units. Each unit requires 225,000 BTUH
Natural Gas.
In this example, we are supplied with 5 psig and
the gas company has stated the specific gravity
of the natural gas is 0.60. Local codes require a
pressure drop of 3.5 psig.
The HVAC Units have been spaced so they are
equal in distance.
1. Determine the total gas load for each appli-
ance in cubic feet per hour:
2. Measure the length of each run and deter-
mine the maximum length from the meter to
the farthest appliance.
A = 75 ft., B = 25 ft., C = 25 ft., D = 25 ft., E = 25
ft., F = 25 ft. G = 25ft. H = 25ft. I = 25ft.
Farthest Unit = A + B + C + H = 75 ft. + 25 ft. +
25 ft. + 25 ft. = 150 ft.
The longest run is from the meter to the last
HVAC Unit at 150 ft.
3. Sizing Section A – Length A must be sized to
handle the total load of all appliances and
the total pressure drop from the meter to the
farthest appliance. The total appliance load
is 1,350 CFH. Using the longest length sizing
method, the length is 150 ft. to the last HVAC
Unit. Referring to Table 11 (5.0 psig; Pressure
Drop: 3.5 psig) under the 150 ft. length column,
we find that 1 inch Parflex tubing (PGP-16) has a flow capacity exceeding 1,350 CFH (1,539 CFH). Use 1
inch Parflex tubing (PGP-16) to run Section A.
4. Sizing Section B – Section B must supply four HVAC Units. The total pressure drop for the system is
considered to be from the meter to the last HVAC Unit. The total appliance load is 225 + 225 + 225 + 225
= 900 CFH. Using the longest length sizing method, the length is 150 ft. Referring to Table 11 under the
150 ft. length column, we find that size 1 inch Parflex tubing (PGP-16) has flow capacity over 900 CFH
(1,539 CFH). Use 1 inch Parflex tubing (PGP-16) to run Section B.
5. Sizing Section C – Section C must supply the final two HVAC Units. The total appliance load is 225 + 225
= 450 CFH. Using the longest length method, the length is 150 ft. Referring to Table 11 under the 150 ft.
length column, we find that 3/4 tubing (PGP-12) has flow capacity above 450 CFH (570). Use 3/4 Parflex
tubing (PGP-12) to run Section C.
6. Sizing Section D – Section D supplies the first HVAC Unit. The total load is 225 CFH and the total length
is 25 ft. + 75 ft. = 100 ft. Refer to Table 11 under the 100 ft. column. We find that 1/2 inch (PGP-8) has
capacity of 225 CFH (363). Use 1/2 inch (PGP-8) to run Section D.
7. Sizing Section E – Section E supplies the second HVAC Unit. The total load is 225 CFH and the total
length is 25 ft. + 75 ft. = 100 ft. Refer to Table 11 under the 100 ft. column. We find that 1/2 inch (PGP-8)
has capacity of 225 CFH (363). Use 1/2 inch (PGP-8) to run Section E.
8. Sizing Section F – Section F supplies the third HVAC Unit. The total load is 225 CFH and the total length
is 75 ft. + 25 ft. + 25 ft. = 125 ft. Referring to Table 11 under the 125 ft. column, we find that 1/2 inch
(PGP-8) has capacity above 225CFH (326). Use 1/2 inch (PGP-8) to run Section F.
Parallel Elevated System
Appliance Loads
Lengths
Tube Size
-
A = 75 ft.
PGP-16 (1")
B = 25 ft.
PGP-16 (1")
C = 25 ft.
PGP-12 (3/4")
HVAC Unit (225 CFH)
D = 25 ft.
PGP-12 (3/4")
HVAC Unit (225 CFH)
E = 25 ft.
PGP-8 (1/2")
HVAC Unit (225 CFH)
F = 25 ft.
PGP-8 (1/2")
HVAC Unit (225 CFH)
G = 25 ft.
PGP-8 (1/2")
HVAC Unit (225 CFH)
H = 25 ft.
PGP-8 (1/2")
HVAC Unit (225 CFH)
I = 25 ft.
PGP-8 (1/2")
Total 1,350 CFH