posted 10 years ago
The diagram didn't come through, but you will definitely not be able to run ducting the way you describe. The standard recommendation is that an 8" system can power up to 50' (15m or so) of horizontal duct, MINUS 5' for each 90 degree bend. You can see the difficulty.
What you might possibly be able to do is create a series of bells, largeish chambers where the hot air enters at the bottom and rises, then falls as it cools, with only the coolest air leaving via an exit at the bottom. These have been done in sequence before, though I don't know about three of them. A major benefit of bells is that friction is much less, only involving the connecting ducts and minor entry/exit losses.
You are right that a higher roof some distance away could affect the draft in a chimney. Each situation is different, but a general rule in the US is that a chimney must be at least 2' higher than any part of the roof within 10'. How much difference in height do you have, and what horizontal distances?