Which damper is required at the termination point of a mechanical exhaust discharge?

Which damper is required at the termination point of a mechanical exhaust discharge?

• A. A back draft damper
• B. A fire damper
• C. A motorized damper
• D. A relief damper

Answer: (A)

At the end of a mechanical exhaust duct, the main purpose is to prevent air from flowing backward into the building when the fan isn’t exhausting or when outdoor conditions try to push air back through the duct. A backdraft damper accomplishes this by staying closed when there’s no exhaust flow and opening only to let air out when the fan is on. This keeps drafts, odors, and unwanted air infiltration from disturbing the conditioned space and helps maintain the proper indoor pressure relationship. Other dampers serve different roles. A fire damper protects against fire spread through ducts at fire-rated barriers, which is a separate requirement tied to fire resistance. A motorized damper is an optional control device used where automatic control is needed, not a universal termination requirement. A relief damper is used to relieve excessive pressure, not primarily to prevent backflow at the outdoor discharge.

At the end of a mechanical exhaust duct, the main purpose is to prevent air from flowing backward into the building when the fan isn’t exhausting or when outdoor conditions try to push air back through the duct. A backdraft damper accomplishes this by staying closed when there’s no exhaust flow and opening only to let air out when the fan is on. This keeps drafts, odors, and unwanted air infiltration from disturbing the conditioned space and helps maintain the proper indoor pressure relationship.

Other dampers serve different roles. A fire damper protects against fire spread through ducts at fire-rated barriers, which is a separate requirement tied to fire resistance. A motorized damper is an optional control device used where automatic control is needed, not a universal termination requirement. A relief damper is used to relieve excessive pressure, not primarily to prevent backflow at the outdoor discharge.