What is the base capacity of a 6-inch vent before the reduction?

What is the base capacity of a 6-inch vent before the reduction?

• A. 122 MBtu/h
• B. 110 MBtu/h
• C. 167 MBtu/h
• D. 186 MBtu/h

Answer: (D)

In vent sizing, the base capacity is the amount of gas input a vent size can carry before any reductions are applied. It’s determined by the vent diameter: larger diameters allow higher base capacities because they can move more exhaust without restriction. For a 6-inch vent, the base capacity is 186 MBtu/h, which is why that value is the correct choice. This is the starting point you use before accounting for reductions due to vent length, number of fittings, number of appliances on the same vent, and other installation factors. If the total input of the connected appliance(s) after applying those reductions is within this base capacity, the 6-inch vent is adequate.

In vent sizing, the base capacity is the amount of gas input a vent size can carry before any reductions are applied. It’s determined by the vent diameter: larger diameters allow higher base capacities because they can move more exhaust without restriction. For a 6-inch vent, the base capacity is 186 MBtu/h, which is why that value is the correct choice. This is the starting point you use before accounting for reductions due to vent length, number of fittings, number of appliances on the same vent, and other installation factors. If the total input of the connected appliance(s) after applying those reductions is within this base capacity, the 6-inch vent is adequate.