The fire doesn't really form a vortex too well. Since it's own heat is what's creating the updraft, it seems to just try shrink smaller and smaller until the fire is just a narrow stream. If you "injected" fire in from a side you could probably get a proper funnel to work, but I don't want to risk melting my machine 
The fire itself does provide a very strong updraft, I can get a tornado the whole length of the machine from that fire alone, without the top fan on. You can stick your hand in the funnel further up and feel the intense heat. Since the updraft is also being provided at the bottom, sticking your hand above it doesn't disturb it, it's a cool effect.
The fire itself does provide a very strong updraft, I can get a tornado the whole length of the machine from that fire alone, without the top fan on. You can stick your hand in the funnel further up and feel the intense heat. Since the updraft is also being provided at the bottom, sticking your hand above it doesn't disturb it, it's a cool effect.
