Height: the taller the chimney, the more draft it will produce at a given temperature difference.

Why does chimney length affect draft?

Draft size needs to be correlated to the capacity that the flue can exhaust. What is this? The reason that a taller chimney creates a better draft is really rather simple as the higher up in the atmosphere the chimney reaches, the greater the differential pressure.

Can a chimney be too long?

A chimney that's too tall can result in the heated air cooling off by the time it reaches the top of the chimney stack. This can create a negative pressure inside of the smokestack that pushes smoke and other gases back into the home.