How to make ceiling vent go around ceiling beam?

Question

I discovered my house kitchen vent doesn't actually vent anywhere. Since I cook a lot of Chinese food, it means the air is always oily.

I bought a brand new high-powered ceiling fan, pulled out the old unit and and installed this with the help of an electrician. The plan was to drill a 6" hole directly above, which is an attic crawl space, then to add another 10 feet of horizontal 6" pipe to let it vent out a horizontal wall of the house.

But in trying to make a 6" hole above the cabinet, I found that directly above the vent is huge ceiling beam, that is 3" wide and probably 8" tall. I really don't want to cut this beam, especially as it appears the entire cabinet is hanging under this.

So, if I send the 6" ducts directly up, they are met by this huge wooden beam cutting through 3" of it. There is only about 3" free space one side of the beam where I could go around it.

If I redirect the pipe anywhere but directly up, it requires making the pipe visible and sending it through multiple walls to the outside; something the wife won't agree too.

I think I could crush some bendy vent pipe to fit, but worry that would reduce the air flow significantly:

What I think I need to get around this problem is some kind of fixture that is similar to this vaccuum attachment (pictured), going from a circular shape to a broader shape:

It there any adapter that goes from 6" inch circular duct to something like a 3"x12" wide shape and back, so I can fit it around the giant beam, without having a loss of air flow?

Answer 1

Your idea is quite reasonable, and there are round-to-rectangular vent adapters listed at Home Depot and Amazon, for example. you might use two to transition across the beam, and back to round pipe to the outside vent.

A transition from round to rectangular cross-section could restrict airflow, to some extent. To reduce the risk of fire, clean the duct, perhaps yearly, since you state cooking with oil is frequent.

That said, any outside ventilation would be far better than accumulating oil in the hood or attic!

Answer 2

Yes, of course. With the constraint you have it might be worth having a local HVAC company build you a custom adapter rather than try to find pre-made ones to suit. You also don't need to go back to round after passing the beam, or if you do you haven't explained the reason you think you do.

Here's an example of a round-to-rectangle duct adapter.

Image source, no endorsement.