|First fire with perfect draft (right makeup air channel visible)|
|smoke stays in the chimney|
|left side makeup air channel (partly closed)|
In places where the oven is part of an indoor environment, the combustion air will be taken from wherever it is available (doors, windows, heating system, etc.)
Where there is negative air pressure in the space due to other exhaust fans, smoke may come down the chimney and make using the oven impossible. Other factors effect draft, such as chimney height and size.
In the recent brick oven build at Brewster Academy, two makeup air chambers were built into the masonry that surrounded the flue space. These provide immediate and passive air equal to the rate of natural draft the chimney provides while also giving the fire combustion air precisely where it is needed. The openings can be adjusted and the chimney has a damper for when there is no fire in the oven.
As a late-arriving detail, this solves a number of issues that indoor wood-fired brick ovens face.
I always try to make improvements based on my continuing experience building and using brick ovens.