Makeup air is required when a clothes dryer exhaust exceeds which threshold?

Makeup air is required when a clothes dryer exhaust exceeds which threshold?

• A. Makeup air is required for any dryer regardless of CFM
• B. Makeup air is required when exhaust exceeds 200 CFM
• C. Makeup air is never required for clothes dryers
• D. Makeup air is required only for gas dryers

Answer: (B)

Air balance in a home becomes a concern whenever a clothes dryer exhausts air to the outdoors. The vent pulls warm, humid air out, and without replacement air the indoor pressure can drop, increasing the risk of backdrafting and related safety or comfort issues. The point at which makeup air is required is when the exhaust rate reaches 200 cubic feet per minute. If the dryer exceeds 200 CFM, makeup air must be provided to replace the air being vented, helping maintain proper indoor pressure. This makeup air can come from a passive outdoor opening or a dedicated mechanical makeup air system. It isn’t about electric versus gas—it's about how much air is being exhausted. Many residential dryers operate below the threshold, but when the exhaust is high or venting is long or complex, makeup air becomes necessary.

Air balance in a home becomes a concern whenever a clothes dryer exhausts air to the outdoors. The vent pulls warm, humid air out, and without replacement air the indoor pressure can drop, increasing the risk of backdrafting and related safety or comfort issues. The point at which makeup air is required is when the exhaust rate reaches 200 cubic feet per minute. If the dryer exceeds 200 CFM, makeup air must be provided to replace the air being vented, helping maintain proper indoor pressure. This makeup air can come from a passive outdoor opening or a dedicated mechanical makeup air system. It isn’t about electric versus gas—it's about how much air is being exhausted. Many residential dryers operate below the threshold, but when the exhaust is high or venting is long or complex, makeup air becomes necessary.