Best way of ducting roof fan?

[Rag]

What is the best way for me to attach ductwork to this opening? It is for simple dust extraction in my warehouse for a fumehood directly below. Im debating between square or round duct, but how would I go about even attaching square duct in the first place?

Would I have to bend out four tabs on each side?

(PS Not an HVAC guy, wont install furnaces/boilers etc)

This is just for a 15ft straight run of ductwork.

 

[Rag]

Anyone?

 

[Sponsor]

 

[WorthFlorida]

You'll probably need to get a sheet metal duct fabricator. Essentially a metal box with one side open and the sides flanged outward to push up against the ceiling. Use this flanges to screw it in as you stated. For the bottom it depends one your hood if it is round or square. If it is round it makes it much easier since there are plenty of round reducers but you cut a hole in the square box and use this starter collar. The box is called a Return Air Box .

https://www.homedepot.com/p/17-5-in-x-28-in-Return-Air-Box-Assembly-RAB-17/202771116
https://www.homedepot.com/p/14-in-S...PIPHorizontal1_rr-_-202771116-_-100136011-_-N

 

[Rag]

You'll probably need to get a sheet metal duct fabricator. Essentially a metal box with one side open and the sides flanged outward to push up against the ceiling. Use this flanges to screw it in as you stated. For the bottom it depends one your hood if it is round or square. If it is round it makes it much easier since there are plenty of round reducers but you cut a hole in the square box and use this starter collar. The box is called a Return Air Box .

https://www.homedepot.com/p/17-5-in-x-28-in-Return-Air-Box-Assembly-RAB-17/202771116
https://www.homedepot.com/p/14-in-S...PIPHorizontal1_rr-_-202771116-_-100136011-_-N

Thanks WesternFlorida!

All I was looking for! The hood below is just a stainless steel commercial kitchen hood and has no collars or attachments. So there will have to be a hole cut in the top of it. (It isn't one of those vent-a-hoods that are popular) Just flat on top. I am assuming then, the easiest might be to just get regular duct (custom made size by fabricator) as you mention, and do the 4 tabs to connect to ceiling and then down onto the flat fume hood attaching the same way with tabs. Does this sound ok?

Also what do you sheet metal guys do with the small gaps in the 4 corners of the duct attachment formed by folding up tabs? Do you use duct butter, or just apply tape over it?

 

[WorthFlorida]

In this situation you probably just use thick foam weather stripping around the vent to act like a gasket.