oh boy did you come to the right place to ask about Cupolas!
the first thing you want to think about is how much metal you want to tap and if you you have the coke and iron to do it. i run a little furnace i named the "Wee Beastie". 30"tall 8"ID. she taps 35lbs in 6-7 min and 50lbs in 10-12 min. she works great in our foundry. i also have a few larger furnaces that can make LOTS of iron.
look at this list of furnaces to help you think about what you want for your self.
http://picasaweb.google.com/ironguild/IronCupolaCatalog#you can also email
Ironguild@gmail.com for more info about furnaces.
Josh
the Iron Guild
