What is a chimney?

[Puy de Dome]

Ok ok, I know what a chimney is - I think... it's a conduit for hot air and smoke and other stuff to escape to atmosphere...

... but is it simply a glorified elongated hole?

If I have a rectangular vertical passage lined with brickwork, can I put a slab of something (marble/stone/whatever) on top of it, make a big hole in it and glue a metal tube of say 5" on top?

Is it more complex than that?

Thanks

PdD

[dmun]

The lower part, at least, of your chimney gets very hot. Whatever material you use for your transition from entry to flue pipe should resist heat. As they cool, flue gases condense and let off acidic substances on the inside of the chimney. Therefore the upper part of your chimney should be non-corrosive. Single wall stove pipe will rot out in a couple of seasons for this reason. If your oven is freestanding, and not subject to building inspection, yes, the chimney is more or less a vertical pipe with a little funnel shape at the bottom. If it is built into a structure, and has to conform to code, then it gets somewhat more complicated.