My forge is located two steps from my garage door, when i open my walk door and the garage door at the same time i get a natural draft, unless the wind is absolutely still.
A hood and chimney over the forge would probaly be a good idea, the chimney would draw of its own. I have seen forges vented out the side wall with a hood and blower. I think this all kinda depends on the location, and kind of building you are using.
I still want to build an open air forge area, I think that would be ideal for me, roof with a large overhang, half wall and shutters to close up shop when not in use.
Ahhh, one of these days.
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Sola Fide