To keep outdoor air ductwork clean, what is recommended?

• A. Install UV lights in the ducts
• B. Clean ducts monthly with solvents
• C. Use metal ducts only
• D. Install filters at the outdoor air intakes

Answer: (D)

Filtering incoming outdoor air at the intake is the most effective way to keep outdoor air ductwork clean. Outdoor air carries dust, pollen, soot, and microbial particles that can deposit on ducts and coils, fostering buildup and reducing system efficiency. By placing filters right at the outdoor air intakes, you intercept these contaminants before they enter the ventilation system, which helps minimize inside-duct fouling and lowers maintenance needs while improving indoor air quality.

UV lights inside ducts can help control microbes on surfaces but they don’t remove particulates, and they require careful design and maintenance. Cleaning ducts with solvents on a monthly basis is unnecessary and can leave residues or damage ductwork. Relying on duct material alone (like using metal ducts) doesn’t guarantee cleanliness and doesn’t address incoming contaminants. Filtering at the intake directly addresses the source of most outdoor contaminants, making it the recommended approach.