Fireplaces, Heating Stoves, Flues and Chimneys - Moving Boiler and Hot water Tank Chimney

Not sure if this is the right place for thsi question, if not ...sorry.

I am remodelling the kitchen. The boiler and hotwater chimneys tie together and go up through a wall that is being removed. (Hopefully)

I want to repipe the chimneys about 8 feet over to another wall and make the chimney chase, run it up the new wall and then back over to the old chimney pipe, once it get back into the attic. (This will save punching a new hole in the roof)

Unfortunatley where the new chimney will need to run is the hot air duct work (main header). To make this work I will need to shorten the hot air main header by two feet and move the take offs further up stream. This will mean a few more elbows in the system. Is there a problem with this? Also how does on go about cutting the main duct?

hmm this is a complex operation that isnt easily answered without fully understanding the nature of your design; best of luck!

Not there cant see it. But i sure dont want to say put 4 L in my flue pipe. That to add more L's to the heat runs ??? One L is like 5 more ft of drag on the run.
To cut the duct get a left and right hand snips cut like a 2" slip out of it. Hammer a screwdriver sideways in the duct to start.

ED