What is the minimum size of a single wall metal pipe vent on a gas water heater?

The minimum size of a single wall metal pipe vent on a gas water heater is 3 inches. This specification is based on the need to ensure adequate venting for combustion gases produced by the water heater. A vent that is too small might not effectively carry away the combustion byproducts, which could lead to dangerous situations such as carbon monoxide buildup or incomplete combustion.

In certain installations, local codes or manufacturer specifications may dictate larger vent sizes, but for standard applications, a 3-inch vent is generally accepted as the minimum. This size allows for proper draft and reduces the risk of condensation within the vent, which can lead to corrosion and other issues over time. Proper venting is crucial to the safe operation of gas appliances, and adhering to the minimum size requirements helps maintain safety standards and efficiency in gas water heaters.