What is the adjusted capacity for a 5- inch vent when three elbows are used?

What is the adjusted capacity for a 5- inch vent when three elbows are used?

• A. 110 MBtu/h
• B. 122 MBtu/h
• C. 167 MBtu/h
• D. 100 MBtu/h

Answer: (A)

When sizing a vent, every fitting adds friction and reduces the effective capacity. For a 5-inch vent, the straight-run base capacity is typically 125 MBtu/h. Each elbow reduces capacity by about 4% for this size, so three elbows total a roughly 12% reduction. 125 MBtu/h × 0.88 = 110 MBtu/h. So, the adjusted capacity with three elbows is 110 MBtu/h.

When sizing a vent, every fitting adds friction and reduces the effective capacity. For a 5-inch vent, the straight-run base capacity is typically 125 MBtu/h. Each elbow reduces capacity by about 4% for this size, so three elbows total a roughly 12% reduction. 125 MBtu/h × 0.88 = 110 MBtu/h. So, the adjusted capacity with three elbows is 110 MBtu/h.