Any advice would be much appreciated!

I've tried reading up on georgia hvac codes, but I can't make heads or tails of them.

I'm trying to figure out if I can condense a 4ftx2ft space that goes from the basement up to the attic and it contains hvac/exhaust stuff. It takes up valuable space in both the kitchen and the second floor master bathroom. I've attached a rough sketch of what is inside the wall and approximate space between everything.

I would imagine there are codes on how much clearance has to be around the flue pipe? Can the exhaust be routed out the side of the house and not the roof if it isn't a high efficiency furnace/hot water heater?

It just seems like there is a whole lot of wasted space that I would much rather use in the kitchen!

Thanks!