Installation Guide

17
Sizing Methods and Examples
Step 6 Size Section F: Determine the total length and load.
• The BBQ load is 50 CFH and the length is 60 feet (A + E + F).
• ½" Tubing has a maximum capacity of 96 CFH at 60 feet so ½" is the correct size.
Step 7 Size Section G: Determine the total length and load.
• The water heater load is 25 CFH and the length is 50 feet (A + E + G).
• ½" Tubing has a maximum capacity of 104 CFH at 50 feet, so ½" is the correct size.
Hybrid CSST & Black Iron Rigid Pipe Systems
In low and medium pressure systems with high loads and/or long runs, it can be advanta-
geous to use both black steel pipe and HOME-FLEX® tubing to minimize pressure drops.
Sizing Hybrid HOME-FLEX® and Black Iron Systems
Proper sizing of hybrid HOME-FLEX® and rigid black steel pipe requires the use of the standard
gas piping capacity tables used for black steel pipe (these can be found in many plumbing
and mechanical codes as well as the National Fuel Gas Code) as well as the HOME-FLEX®
capacity tables in this manual. For your convenience, a black steel capacity table for sizing is
printed in Table 7.11 (p. 46) of this book.
Example 5: Low Pressure Hybrid System in a Series Arrangement
The system in Figure 3.9 is a commercial building with three unit heaters and a water heater.
The source is standard low pressure with a 6 inch w.c. supply and 0.5 inch w.c. maximum
allowable pressure drop. Sizing this system requires sizing the rigid black pipe section as well
as the HOME-FLEX® CSST runs to the appliances.
Step 1 Size the rigid black steel pipe: Determine
length of longest run and total load.
• The longest run from the meter is A1 +
A2 + A3 + A4 + E = 70 feet.
• Total load is 600,000 BTUH = 600 CFH.
Consulting Table 7.11, at a 70 foot
length, the diameter of black steel
pipe that can supply 600 CFH or greater is 1½" with a maximum capacity of 750
CFH. The correct size for section A1 is 1½".
• To size section A2, we can reduce the load already carried by A1, in this case 200
CFH from the rst heater. The length, however, remains 70 feet. Total load then is
A1 A2 A3 A4
B C D
E
Gas
Meter
Low Pressure
(6" w.c.)
60,000
BTUH
200,000
BTUH
Heater
200,000
BTUH
Heater
200,000
BTUH
Heater
Water
Heater
Figure 3.9 Low Pressure Hybrid System—Series Arrangement
Length of Runs:
A1 = 10' A2 = 20' A3 = 20' A4 = 5'
B = 10' C = 10' D = 10' E = 15'
Supply Pressure: 6" w.c.
Pressure Drop: 0.5" w.c.