A drip leg is required at the base of how many risers when water vapor is present in gas?

A drip leg is necessary at the base of all risers in a system where water vapor is present in gas. This is critical because water vapor can condense within the gas supply line, leading to the accumulation of liquid water that can affect the performance of the gas appliances and systems downstream. By having a drip leg at each riser, any collected condensate can effectively drain away, preventing potential issues such as corrosion, gas blockages, or equipment malfunction. This requirement adheres to safety protocols and ensures that the gas remains uncontaminated, promoting efficiency and reliability in gas delivery systems.