Gas Fitter Practice Test

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What is the minimum size of a single wall vent connector for a natural draft appliance with an input of 1,000,000 Btuh?

8 inch diameter
10 inch diameter
12 inch diameter
16 inch diameter

The correct answer is: 12 inch diameter

For a natural draft appliance with an input of 1,000,000 Btuh, the minimum size of a single wall vent connector is determined by the standards set in the National Fuel Gas Code (NFPA 54) or the Uniform Mechanical Code (UMC). Generally, the sizing of vent connectors is necessary to ensure proper draft and to prevent excessive backpressure or flue gas spillage. When calculating the minimum diameter for vent connectors, the value of the appliance's input is essential since larger input ratings require larger vent diameters to facilitate adequate airflow and venting capacity. As per the codes, a natural draft appliance with an input of 1,000,000 Btuh is recommended to use a vent connector diameter of at least 12 inches to ensure safe and efficient operation. Selecting a diameter that is too small could lead to inadequate venting, posing safety risks such as combustion gases returning to the appliance or the living area. Therefore, the choice of a 12-inch diameter as the minimum size is based on these critical guidelines and ensures that the venting system operates within safe limits.