Condensation was my thought. The chimney contains three flues. The flue we intend to use was for an aga which is no longer there, so no, there would not be a fire there. The next flue is for the living room. In autumn/winter/spring the woodburner would generally be lit in the living room while we are cooking so the flue should be warm (hence my thought that we should have a proper liner in the chimney, rather than just run a the flexible plastic extraction tube up there). However, in the summer, the flue will be cold, so would the steam make it all the way to the top, or would it condense in the ducting and just dribble back down again?
External wall is not really an option as they are too far away from the stream cooker, the walls are too thick and crumbly etc. I'd prefer not to have one in the window as it is such a cold room and we have suffered a window fan previously