What is the length of the vent system?
The length of vent system and number of elbows should be kept to a minimum to provide efficient performance. The maximum equivalent length of the vent system is 60 ft (18.3 m). For altitudes above 4,500 ft (1372 m), reduce recommended vent run by 20% for best performance.
Was the correct vent material used?
Use 26-gauge minimum galvanized or 25-gauge minimum aluminum metal vent. Poor quality pipe fittings can reduce airflow. Flexible metal vent is not recommended. Metal duct may be reduced to 30-gauge galvanized steel or 26-gauge aluminized steel if allowed by local codes. This reduction is based on information in the International Residential Codes Section M1601.1 (2006 edition).
NOTE: Local codes may require a heavier gauge material.
How many elbows were used?
- Use no more than three 90° elbows.
- Do not install 2 elbows together. Make sure there is a minimum of 18" (45.7 cm) of straight vent between the elbows if more than one elbow is used.
- If an elbow is used, install it as far away as possible from the hood’s vent motor exhaust opening.
- Elbows too close together can cause excess turbulence that reduces airflow.
- Do not use a 5" (12.7 cm) elbow in a 6" (15.2 cm) or 3¼" x 10" (8.3 x 25.4 cm) system.
Follow the instructions below for best performance:
- Do not reduce to a 5" (12.7 cm) system after using 6" (15.2 cm) or 3¼" x 10" (8.3 x 25.4 cm) fittings.
- Avoid forming handmade crimps. Handmade crimps may restrict airflow.
- Use a vent cap for proper performance. If an alternate wall or roof cap is used, be certain the cap size is not reduced and that it has a back draft damper.
- Use vent clamps to seal all joints in the vent system.
- Use caulking to seal exterior wall or roof opening around the cap.
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