For a water heater installed in a residential attic, the drain pipe must be at least what size?

For a water heater installed in a residential attic, the drain pipe must be at least what size?

• A. 1/2 inch
• B. 3/4 inch
• C. 1 inch
• D. 1 1/4 inch

Answer: (B)

When a water heater is installed, the discharge path from the relief valve (and from any drain pan) must be able to carry the potential flow if the valve ever opens. The outlet on common residential water heater relief valves is a 3/4 inch size, and codes require the discharge piping to be at least that size to avoid bottlenecks that could trap hot water or steam. In an attic installation, a clear, adequately sized drain path is especially important to prevent water damage from any overflow, so using a minimum of three-quarters of an inch ensures reliable drainage. A smaller pipe would risk blockage or backflow, while a larger pipe isn’t required by the standard and adds unnecessary cost.

When a water heater is installed, the discharge path from the relief valve (and from any drain pan) must be able to carry the potential flow if the valve ever opens. The outlet on common residential water heater relief valves is a 3/4 inch size, and codes require the discharge piping to be at least that size to avoid bottlenecks that could trap hot water or steam. In an attic installation, a clear, adequately sized drain path is especially important to prevent water damage from any overflow, so using a minimum of three-quarters of an inch ensures reliable drainage. A smaller pipe would risk blockage or backflow, while a larger pipe isn’t required by the standard and adds unnecessary cost.