Where should drains be provided in horizontal duct runs?

• A. At high points in the horizontal ducts
• B. At the end of the duct
• C. Drains shall be provided at low points in the horizontal ducts
• D. At midpoints between bends

Answer: (C)

Condensate in horizontal duct runs tends to settle at the lowest points due to gravity. Placing drains at those low points lets the collected moisture flow out naturally, keeping the ducts dry, preventing corrosion and mold, and maintaining steady airflow. Drains at high points wouldn’t drain water, since gravity pulls it downward, and draining only at the end or midpoints might miss other low spots. By routing the duct with a slight downward slope toward the drain at each low point, condensate can be reliably removed.