Removing part of a chimney structure.

Hi,

i have a weird question about removing part of a chimney... Here we go..

I live in a 125 year old house that has two chimney flues. One is still attached to the fireplace setting and is functional.

The other is walled over in the kitchen area. I presume it was once used as the primary heat or cooking source.
At this point unless you look from outside the house you cant tell it was even there.

What I want to do is break into the front wall of the chimney and install cabinetry on that wall. Is this possible?

the flue its self is about 6 feet wide. its capped and there are no pipes coming out of the top so it doesn't appear to be used for venting other things...

Majority of the flue structure is outside of the house, you can see it it shares a common wall with the inside, which i assume behind the plaster, is bricked over.

I just want to break into the front facing wall about 8 feet high and 7 feet wide. so longer than the chimney. That doesn't mean i have to break down the chimney walls on the side, I can keep the brick in place as a visual and that would be nice, but I would have to at least remove 8 feet of 1 of the 4 walls, leaving 3 walls for support.

is that enough? Do i have to put in a support beam? How do you do that if it were necessary? Will the whole thing collapse as i try to dig into part of it?

We are on the ground floor of the house, and the flue extends 3 stories. I would be removing brick around the bottom of the flue where i presume the old f mouth was.

Removing part of a chimney structure.