kitchen grease duct through a loading dock.

[rmusa]

We have a 4500 cfm grease exhaust duct tied to a hood. The duct will penetrate wall behind kitchen and then go through a two bay loading dock and then to the exterior. The walls around the loading dock are 3 hr rated.

The duct will have standard 2 hour rating, double wall manufactured with insulation. Fire dampers are not allowed in the duct. How can this duct be installed in the loading dock?
Does the rating of the duct need to be increased to 3 hour? Will 2 hour duct work?
Can we build a 1 hour enclosure around the duct. Is 2 + 1 hour additive?

 

[DrRTU]

Not additive in this case. Build 3 hour chase around the duct to separate the duct from the room. Delta $ between 1 hr and 3 hr. chase would justify the labeling requirements or future questions.

 

[berkshire]

If this is a horizontal grease duct, make sure drain pans and cleanout doors are accessible.
B.E.

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