What is the vent size and maximum input for a water heater rated at 50,000 Btuh connected to a masonry chimney with a 2-foot rise and a height of 25 feet?

To determine the correct vent size and maximum input for the specified water heater, it's crucial to consider the heat input rating and the characteristics of the venting system, particularly when connected to a masonry chimney.

For a water heater rated at 50,000 Btuh, the appropriate vent size for effective gas venting needs to accommodate the products of combustion without causing backdraft or excessive pressure drop. A 4-inch diameter vent is acceptable for this type of equipment given its heating value.

The maximum input of gas (measured in cubic feet per hour, cfh) that the vent can safely handle is influenced by several factors including the height of the chimney and the rise of the vent. In this scenario, the masonry chimney has a 2-foot rise and is 25 feet tall, which allows for a greater draft, making it possible to achieve a higher cfH rating.

Among the choices provided, a 67 cfh output for a 4-inch diameter vent corresponds to the correctly calculated maximum input for this setup, taking into account the rise and overall length of the chimney. Vent sizing tables and codes typically provide these values, ensuring the vent won’t exceed its capacity for those rated inputs, thus maintaining safety and efficiency in operation.