Remove square, and install flex round, change routing

[Jetboy55]

Hello all, thanks for any help you can give. I have done almost no HVAC work, so I need some advice. I am remodeling my main bath (1 story ranch with full basement). The wet wall of the bath is right above this duct work and the duct is making the plumbing work unnecessarily complicated and hard to reach. I want to remove the square (8x12in) ducting, stopping it just to the right of the middle top takeoff in the picture. There is also a takeoff at the end cap at the far left. Both takeoffs are 5 inch round. I would like to end the square duct as mentioned and transition to round, or flexible round to supply the two 5in round ducts, that way I can reroute them so they aren't in the way of the wet wall plumbing. How would I go about doing this? Flexible duct seems the easiest to reroute around the plumbing area, but if that won't work, how else should I do it? Regular round fittings I am familiar with, but how to cap off the end of the 8x12 square duct and have attachment points for the two round ducts is out of my experience. Thanks for the advice and suggestions.

Note: I don't have any HVAC tools beyound aviation snips and normal DIY tools (hand tools, cordless drill, reciprocating saw, jigsaw, ect....).

 

[Breplum]

I highly recommend a pro help.
Just getting air tight connections has lots of details.
I am surely impressed that you have the smarts, but airflow sheetmetal is an art of sorts also.
12 x 8 duct round equivalent is about 10.7". So, 12" is the nearest equivalent.
Rectangular large duct is not stocked much on our west coast but I know rectangular is more popular due to a lot more basements than us.
So, I see online Broan makes an adapter for $100 and I'd venture that local sheet metal shops stock or can readily get.
maybe look up connecting flex to round on youtube.
Use adjustable 12" 90 for tighter bend if you like. Three hex head screws to join sheet metal. You'd need snap-tie tensioning tool and not junky duct tape but "listed" UL181B-FX tape. I guess you heat your basements, so the leaks are somewhat ok even if not tight. But, nevertheless, listed tape will not break down (so the engineers tell us).
Plumbing: Rubber unshielded couplings are not listed for indoors and are somewhat unreliable as they tend to offset under stress.
PVC must be rigidly supported every 4' (no plumber's tape).

 

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[Jetboy55]

Thanks for the info. I am not trying to duplicate the 8x12 duct capacity in round equivalent. Both takoffs that I want to move are 5 inch, so really I just want to change the location of the 5 inch take offs to further upstream so I can shorten the 8x12 for clearance purposes.