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JJ gave a good example. Time and temps will be different in different situations such as where it is placed, the type of fuel, pellets, dust, powder, humidity, airflow and so on. Using pitmaster pellets in a 22cf well insulated smoke chamber, the temps may rise as much as 35°.
If you pipe it in, as with the mailbox mod, there is only a couple of degrees change.
The longer the pipe the less heat will get to the smoker, and the cleaner the smoke will be. So with a long enough pipe there won't be any rise in temps in the smoker.