Installation Guide

15
Sizing Methods and Examples
Step 4 Size Section D: Determine the length from the meter to the water heater.
• A + D = 32 feet, and the load of the water heater is 25,000 BTUH = 25 CFH.
• Table 7.4 shows that ½" tubing has a total load capacity of 116 CFH at 40 feet, so
½" tubing is the correct size.
Step 5 Size Section E: Determine the length from the Range oven to the Furnace.
• A + E= 30 feet and the load of the furnace is 40,000 BTUH = 40 CFH.
• Table 7.4 shows that ½" tubing, with a maximum capacity of 133 CFH, is correct.
Elevated Pressure Systems
Example 3: Elevated Pressure System in a Parallel Arrangement
In this example, an extended tubing run is required from the gas meter to the desired appli-
ance locations. This scenario is common in single and multifamily locations. 2 PSI elevated
systems are ideal for the long runs required in multifamily buildings that have a central gas
meter bank.
Step 1 Size Section A:
• Maximum load = furnace + range oven + water heater + dryer = 190,000 BTU = 190
CFH and the distance to the regulator is 100 feet.
• Supply pressure is 2 PSI and allowable drop is 1 PSI. Table 7.5 is the correct table.
• Scanning the 100' column, ½" tubing has a maximum capacity of 129 CFH which
is not adequate. ¾" Tubing has a maximum capacity of 471 CFH. As this meets or
exceeds our required capacity of 190 CFH, ¾" tubing is the correct size.
Step 2 Size Sections B-E: From the regulator outlet, the system is supplying 8 inches w.c. with
an allowable drop of 3 inches w.c. Table 7.3 is the correct table for this section of the system.
• Section B is 10 feet with a an appliance load of 90 CFH for the furnace. ½" Tubing
has a maximum capacity of 160 CFH at 10 feet, so ½" is the correct size.
• Section C is 20 feet with an appliance load of 40 CFH for the range oven. ½" Tubing
has a maximum capacity of 116 CFH at 20 feet, so ½" is the correct size.
• Section D has a length of 25 feet with an appliance load of 25 CFH. ½" Tubing has a
maximum capacity of 104 CFH at 25 feet, so ½" is the correct size.
• Section E has a length of 20 feet with an appliance load of 35 CFH. ½" Tubing has a
maximum capacity of 116 CFH at 20 feet, so ½" is the correct size.
Gas
Meter
25,000 BTUH
Range Oven
40,000 BTUH
Elevated
Pressure
2 PSI
35,000 BTUH
Furnace
90,000 BTUH
Water
Heater
Furnace
Dryer
Figure 3.7 Elevated Pressure System—Parallel Arrangement
A
B
C
D
E
Length of Runs:
A = 100' B = 10' C= 20'
D = 25' E = 20'
Supply Pressure: 2 PSI
Pressure Drop: 1 PSI to reg.,
3" w.c. from reg. to appliances