Wasn't sure if this would work or not. Its what i have to work with. If i have to ill do something different but if it will work. Its 8 inch pipe going up. I have 6 inch on the roof. It sucked great with my farriers forge. But that was going straight up. Will this work and if so how?

You just have to try it and see if it works for your forge. Most folks like 10" or 12" flues, but your combo might be all you need. Happy forging!

With the wall right there behind the forge, have you thought about going straight back and doing an outside chimney from there on up?  I've seen that set-up work pretty well in the draw department.

Ya ive been debating doing that. I think thats how im going to do it. Less chance of a headache for some people also. Thanks 

Take a look at the Hofi Side Draft Chimney blueprint.

Does it have to be that long? Can you go shorter and smaller?

Good question. No idea.

Looks to be that long so the vertical pipe can clear the roof overhang. I think you could get away with shorter horizontal. 

Its never a good deal going to a smaller diameter pipe in the vertical. Going to a larger dia is good.

10"-12" works great.

You can do this cheap by buying the flat 6" single wall pipe and connecting two together side by side, not stacked. 

Makes sense. If you think of the chimney as an elongated funnel, do you want the wide end down, holding the smoke in, or up, letting it out?

No. Ok. Lets find out. I can make it all square.  Ill post pics when its done. Thanks.