What is the required slope for the horizontal portion of a vent connector on residential oil-fired water heaters toward the chimney, in inches per foot?

• A. 1/8 inch per foot
• B. 1/4 inch per foot
• C. 1/2 inch per foot
• D. 0 inch per foot

Answer: (B)

When venting a residential oil-fired water heater, the horizontal vent run must have a slight slope toward the chimney so condensate can drain out of the line instead of pooling. The required slope for that horizontal section is 1/4 inch per foot.

This value is chosen to reliably move moisture toward the chimney without making the pipe overly steep, which could cause sagging or alignment issues. If there were no slope (0 inch per foot), condensate could pool and hinder venting. A smaller slope (1/8 inch per foot) might not drain effectively, while a steeper slope (1/2 inch per foot) is typically unnecessary and could introduce other installation problems.