Performance test for under cabinet models (rear vented)

 Steps to Diagnose Suction or Noise Issues

1. Remove the baffle filters (the stainless steel grills) to expose the fan grills
2. Prepare two paper towels large enough to cover both fan grills.
3. Turn the unit on speed two or three, and hold the paper towels over the fan grills:
   • If the towels stick flat to the grills: The damper blades are opening properly. That’s a good sign — but we’ll still want to confirm that your duct setup is optimized for maximum airflow.
   • If the towels flutter or fall: The blades may not be opening fully, or there may be a blockage somewhere in the duct system.
4. Next step: Inspect the damper blade on the back
   • Look inside the unit from the outside wall for the small flap (internal damper blade).
   • Ensure it opens fully and isn’t stuck or blocked by debris like drywall dust.
   • If your unit is not vented directly outside, and the duct makes a 90-degree turn straight up the wall, this can significantly reduce airflow if the blade is present, as the damper blade blocks 50% or more of the suction in this setup. To resolve this, remove the blade.
5. Check the external damper (this is your wall cap)
   • Ensure it opens smoothly and isn’t blocked by dirt or obstructions.
6. Inspect the seal
   • Check the connection between the hood and the ductwork for gaps or air leaks. A tight seal improves suction.

Duct Guidelines for Best Performance

Use consistent duct size, shape, and material

• Stick with 3-1/4" x or transition to a higher surface area or longer runs 
• Avoid reducing size, changing shape, or mixing materials (e.g., switching from rectangular to round).
• Best practice: Use semi-rigid or rigid ducting.

Keep ducting short and straight

• Max total length: 14 feet.
• Include at least 12 inches of straight ducting coming directly out of the unit before any bends. If you do a 90º elbow out the back, this will reduce performance and can only be fixed by either venting directly out the exterior wall or switching to the top venting option, where you can at least go up 12" before you make a transition.

Avoid airflow restrictions

• Minimize 90-degree turns.
• Do not reduce duct size — reducing the duct size significantly reduces performance and increases noise.

Tips

• Remove damper blade: If your home already has an external roof or wall cap with dampers, you may consider removing the internal damper blade on the back of the unit to improve suction and reduce noise.
• Do not reduce duct size: Reducing the duct size significantly reduces performance and increases noise.
• Minimize 90-degree turns: Doing a 90º angle out the back, will reduce performance and can only be fixed by either venting directly out the exterior wall or switching to the top venting option, where you can at least go up 12" before making a transition.