How to connect vent duct to roof jack?

[Chris]

We are going to have a 10" round duct installed from our kitchen vent hood and it will exhaust thru the roof. I can't find a roof jack off the shelf anywhere that will fit that large a duct, so we might end up getting one made. So, I don't know what size to make it, and I think it depends on how the duct is attached to the roof jack. The roof jacks I've seen are tapered, wider at the bottom than the top. One person suggested that the *top* of it (the narrow end) should be 10" so you can attach the duct there. Someone else said it should be 10" at the bottom and narrow to 8" at the top.

So, having never attached a duct to a roof jack...how do they normally attach, and what size does it need to be? It's a smooth metal duct.

Thanks, Chris

[Wayne Whitney]

Typically the duct passes through the roof jack, with a rubber flange at the top of the cone of the roof jack making a water tight seal against the side of the duct. So for your 10" diameter duct, your custom roof jack should have a 10" opening at the top of the cone.

Cheers, Wayne

[Joe]

Some building codes also require a storm collar above the roof jack. This is cheap insurance against roof leaks. Some installers will secure the duct with braces before it exits through the roof, then the roof jack is sealed to the duct with silicone sealant and the storm collar in turn sealed the same way. HTH

Joe

[3G]

what you want is a "RCVS series vent" no rubber, no plastic.............just metal.

if your ducting is 8", you need an 8" female end on the bottom of the roof vent adapter

[Deke]

DAmn.

Just how much leakage do you get thru that huge oversized duct back into your house?