Why are back-draft or relief dampers sometimes required in kitchen exhaust designs?

Why are back-draft or relief dampers sometimes required in kitchen exhaust designs?

• A. To prevent reverse airflow when there is negative pressure or door openings and to protect the space from infiltration.
• B. To increase air velocity in the duct.
• C. To reduce maintenance costs.
• D. To improve aroma.

Answer: (A)

Back-draft or relief dampers are used to prevent reverse airflow in kitchen exhaust systems when the building experiences pressure fluctuations, such as negative pressure or when doors and openings are moved. The exhaust hood creates a one-way path for air to leave the kitchen, but if outside wind, opening doors, or other equipment pull air in the opposite direction, air can infiltrate the space through the ductwork. A back-draft damper stays closed unless there’s forward airflow, and then it opens to let the exhaust escape. This blocks the unwanted reverse flow, helping keep odors, smoke, and contaminants from moving back into the kitchen or other parts of the building, and it also reduces energy loss by preventing conditioned air from being drawn out through the exhaust when the system isn’t actively exhausting. Relief dampers work similarly to relieve excessive positive pressure, preventing air from being forced back into the space. This is not about increasing duct velocity or lowering maintenance costs, and it doesn’t directly improve aroma—those are not the functions of these dampers.

Back-draft or relief dampers are used to prevent reverse airflow in kitchen exhaust systems when the building experiences pressure fluctuations, such as negative pressure or when doors and openings are moved. The exhaust hood creates a one-way path for air to leave the kitchen, but if outside wind, opening doors, or other equipment pull air in the opposite direction, air can infiltrate the space through the ductwork. A back-draft damper stays closed unless there’s forward airflow, and then it opens to let the exhaust escape. This blocks the unwanted reverse flow, helping keep odors, smoke, and contaminants from moving back into the kitchen or other parts of the building, and it also reduces energy loss by preventing conditioned air from being drawn out through the exhaust when the system isn’t actively exhausting. Relief dampers work similarly to relieve excessive positive pressure, preventing air from being forced back into the space.

This is not about increasing duct velocity or lowering maintenance costs, and it doesn’t directly improve aroma—those are not the functions of these dampers.