Size section #6 in the drawing above using the longest length method and the pipe sizing tables in the International Fuel Gas Code. The material is schedule 40 black iron pipe.

Steps to Solve

1. Identify the Total Demand First, sum the BTU demands of all outlets connected downstream of section #6.

• Water Heater (Outlet C): 50,000 Btu/h
• Furnace (Outlet D): 110,000 Btu/h
• Range/Oven (Outlet B): 80,000 Btu/h
• Clothes Dryer (Outlet A): 35,000 Btu/h

Total Demand: $$ 50,000 + 110,000 + 80,000 + 35,000 = 275,000 \text{ Btu/h} $$

2. Determine the Length of Pipe Next, use the lengths for each outlet connected to section #6 from the diagram:

• From Point of Delivery to section #6: 20 ft
• From section #6 to Outlet B: 15 ft
• From section #6 to Outlet D: 5 ft
• From section #6 to Outlet A: 8 ft
• From section #6 to Outlet C: 5 ft

Total Length to section #6: $$ L = 20 + 15 + 5 + 8 + 5 = 53 \text{ ft} $$

3. Use Pipe Sizing Tables for Sizing From the International Fuel Gas Code tables, refer to the appropriate section for sizing based on the total demand of 275,000 Btu/h and the pipe length of 53 ft.

4. Calculate the Pressure Drop Considering the maximum allowable pressure drop is 0.5 inches W.C., check the table to find the appropriate pipe diameter for the given demand and length that maintains the pressure drop within limits.

5. Determine the Correct Pipe Size Based on the findings from the sizing tables, the matching pipe size for the demand and the length calculated will help select the right diameter.