Installation Guide

15
Sizing Methods and Examples
Example 4: Medium Pressure Parallel Arrangement with a Series Branch
This installation has a barbecue installed near the water heater. Given the number of appli-
ances, a parallel arrangement was selected for the system, with a single run supplying the
barbecue and the water heater in series.
Step 1 Size Section A: Determine the length of the lon-
gest run (from gas meter to appliance) and total load
required by the system.
• Total system load = range + dryer + furnace
+ water heater + BBQ = 205,000 BTUH =
205 CFH.
• Longest run is from meter to the BBQ: A + E + F = 60 feet.
• Supply pressure is 12-14 inches w.c. (½ PSI), and allowable pressure drop is 6
inches w.c., so Table 7.4 is the correct table.
• At a length of 60 feet, ½" tubing can supply a maximum of 96 CFH. The system
requires at least 205 CFH, so ½" is too small. ¾" Tubing can supply a maximum of
329 CFH. ¾" Tubing is the correct size.
Step 2 Size Section B: Measure the length from the meter to the range to determine
appropriate size.
• Total length is 35 feet (A + B), and appliance load is 40 CFH.
• 35 feet is not an option on the table, so we round up to 40 feet. ½" Tubing has a
maximum capacity of 116 CFH at 40 feet, so ½" is the correct size for this run.
Step 3 Size Section C: Determine the length from meter to the dryer:
• Total length is 35 feet (A + C) and appliance load is 30 CFH for the dryer.
• ½" Tubing has a maximum capacity of 116 CFH at 40 feet so ½" is the correct size.
Step 4 Size Section D: Determine the length from the meter to the furnace.
• Total Length is 45 feet (A + D) and appliance load is 60 CFH.
• ½" Tubing has a maximum capacity of 104 CFH at 50 feet so ½" is the correct size.
Step 5 Size Section E: Determine the longest length and total load for the section. As there are
two appliances serviced by this run, it is calculated as a series layout like Example 1.
• Section E serves both the water heater and BBQ, so total load is 75 CFH.
• The longest length is from the meter to the BBQ (A + E + F) = 60 feet.
• ½" Tubing has a maximum capacity of 96 CFH at 60 feet so ½" is the correct size.
Gas
Meter
Water
Heater
25,000 BTUH
Range Oven
40,000 BTUH
Med Pressure
(12-14" w.c.)
1/2 PSI
60,000 BTUH
Furnace
BBQ
50,000
BTUH
30,000 BTUH
Dryer
Figure 3.7 Medium Pressure System—Parallel Arrangement with Series Branch
A
B
C
D
E
G
F
Length of Runs:
A = 25' B = 10' C = 10' D = 20'
E = 20' F = 15' G = 5'
Supply Pressure: 12-14" w.c.
Pressure Drop: 6" w.c.