The size of the duct will determine the total CFM rating that is possible with any range hood, regardless of the brand, model, or blower strength. Please review the details below regarding how much CFM each duct size can handle.

CFM Rating by duct size

How the square inch opening impacts suction

The square inch opening of the duct is a crucial component in determining how much suction a range hood will have and effective it will be.

Ducting Scenario Example

Components:

• 750 CFM Twister 30" Range Hood
• 6" Duct Size
• 6" Metal Wall Cap from VICTORY

A 6" duct size has a square inch opening of ~ 28 inches. The VICTORY 6" Wall Caps are made with a square inch opening of at least this size to allow for the full function of the unit.

The Twister model in this scenario has a 750 CFM blower internally, and the unit comes with 8" and 6" duct size options. Selecting the 6" duct size will limit the range hood to 600 CFM maximum. The unit is made to work with both duct sizes and is tested with both for good performance and noise levels.

Reducing the duct size to anything lower than 6" will reduce the square inch opening. Reducing the outside wall or roof cap to a vent with a smaller square inch opening would also impact suction.

How square inches impact suction:

Example 1 - Reducing a 6" duct size to a 5" duct

• The square inch opening is reduced from 28" to ~ 19.6"
• This is a square inch reduction of 30%
• It is safe to expect a 30% reduction in overall suction and efficiency
• The estimated CFM of one of our 600 CFM range hoods with a 5" duct is ~ 400 CFM

Example 2 - Using an inadequate or smaller than recommended wall cap or roof cap

Some wall and roof caps have a smaller than required duct opening in order to achieve a slimmer or more aesthetically pleasing design, but this is not ideal for suction.

• In this example, the square inch opening is reduced from 28" to ~ 22"
• This is a square inch reduction of 21%
• It is safe to expect a 21% reduction in overall suction and efficiency
• The estimated CFM of one of our 600 CFM range hoods with this type of vent cap is ~ 475 CFM

Getting help with CFM calculations

If you require assistance with calculating the expected CFM rating of your new VICTORY range hood, please contact our team at support@victoryrangehoods.com or create a Support Ticket online.