Looks like a just a widening where the metal chimneys entered. Maybe something to help with the updraft.

But I'm not sure why you're concerned about this. Is there an attic above? That's where I'd start disassembling the chimney. From the top down - brick by brick until I was at room level.

My WAG is that the bottom 5-6' is solid brick. The box on top and above the ceiling has probably a 8" flue. Start jn the attic and work your way down. Drape with plastic first to control dust. A 12 year old neighbor boy would be real handy about now.

Yeah, that is what I will be doing. Starting in the attic. I just wanted some opinions because I thought they might have been added to support weight making the chimney load bearing (one protrudes into what I believe is a load bearing wall). I doubt it is, but I just wanted some opinions/advice before I start bringing it down in case someone has a chimney like this and wants to caution me to not take it down without shoring up the wall

Just smash it down. The protrusions don't impact anything that isn't chimney, and you're removing that

Start in the attic at the top

Knock the bricks into the chimney one at a time and have someone at the bottom with a flat shovel to remove them as they fall. Toss them into a five gallon bucket and haul them out .

Large masonry sawzall blade

^^^^This is the way to minimise havoc and dust in the attic and upper floor room. It’s how tower chimneys are disassembled by steeplejacks.

Use the chimney as a trash chute of course. If you got a hand truck/horizontal dolly, you can put a large plastic container (think mid height storage containers) on top of the dolly and push it inside the chimney to make cleanup easier. Some cardboard laying in the bottom of the plastic container will soften the impact of demolished material and prolong the container integrity and life. About 3/4" thick of cardboard worth from the attic, and an additional 0.5" thicker for each floor more than one (yes it's over kill). Replace as necessary, and always before the bottom layer is damaged, including being crushed. If it's crushed but not torn/penetrated, put that layer on top of a new cardboard stack.

And if you don't have a hand truck, it's worth the investment for any home. You don't use it every month, or perhaps year, but damn does it save your back!

Mulching flowerbeds? Throw the bags on the dolly. Tearing out a concrete foundation home play set? Chain link fence? A hideous looking rock garden? Invasive hedge rows? Did the creek in your backyard flood and deposit driftwood? Throw that shit in the dolly. Hand trucks are easier than using a wheel barrow to transport to the dumpster or whatever. Just get 6" castors/wheels or larger for outdoors, and 3 or 4" castors for indoors, with the thickest rubber you can find for longevity. A wider wheel works better in irrigated/wet lawns than a narrow one of course. Also, don't buy a plastic hand truck; get all metal parts excluding tires.

Now I'm thinking about using my hand truck to carry groceries inside with one trip. Maybe I can start using it weekly! The possibilities of use are endless, really. My hand truck is older than I am too.

Furthermore, do you run a bar or venue? There are keg dollies with a curved skeleton to safely move 1/2 barrel kegs from storage to tap. Some even have an adjustable gravity latch to lock the keg in place for smooth handling.

Paid for by Big Hand Truck Manufacturing of America. /s

This reads like a newspaper consumer op-ed. It ain't. Just a fan of not fucking my back up anymore than it already is. Get a 2 in 1 hand truck dolly. You'll thank yourself for it.

It is very difficult to comment here effectively without a site visit. When joists rest on ledges around a chimney they are surely doing some “work” structurally. Starting in the attic and working your way down you will quickly find out what the chimney is really holding.

> added to support weight

I doubt it. The chimney is the last thing you want as a structural support for joists or rafters. If anything, you want as little wood touching it as possible because of the fire risk.

Bit by bit disassembly is the way you'll see if it's supporting anything important.

Look I’ve read the comments and I’m a master mason with over 30 years, almost 40, of experience. First the picture isn’t good enough to make any suggestions with a clear conscience.Without a full picture I wouldn’t give you any advice except to go get the original blueprints at the abatement company in your county or town that will show the construction of it. If it’s not original then you should get a professional chimney service to look at it. The cost is minor considering what damage could be done by having no information. I’m sure you can DIY this even if it’s gas. Most of these are just facades with a galvanized double tube that was already removed when the roof was done. There are just to many variables for me to give you advice. I read how you should do several different things all of which could cause serious damage and injury. I can give you a list of my certifications that show how experienced I am. There’s nothing that’s worse than to have a collapse because you took out a structural member. I hope this helps you and at least gives you some direction. Chimney companies will charge for their time but they will also give you a lot of information and of course having the prints are great to see exactly what your home footprint is and if you’re going to need permits. That can get expensive if you change something on your home and the city hits you with a fine and you have to use a licensed contractor. In other words get information from the sources available not here. Good luck and god bless.