Really underground garage
Join Date: Aug 2010
Location: mnts of Va
Independently owned muffler shops can be a huge resource for under 4" tubing.
After that,its a sheet metal shop.And NOT necessarily an HVAC joint(ha).A roofing biz can and will have scraps/drops of heavier than typical HVAC metal,usually for the asking.
There's a cpl ways to make a sleeve for your connection,if you're the type that wants to keep it in house.If you came in our shop I'd give it to you,takes all of a cpl minutes.It can be an in'y,or an out'y...haha.Inside is quicker by a minute or so.But the outer is a touch more secure.The combination of BOTH,is bullet proof.
Good luck with your project,BW