A long time ago Jerry Frisch told me that a "fix" for ovens that are poorly built or don't draw well was to add more air in the back or side of the oven. For a long time I never did add air since not needing it was (I thought) the mark of a well-designed oven.
Then we built our Office Oven with the experimental combustion chamber underneath. That seemed to be a failure but I began using it to add air - when starting a fire I crack the clean-out door to the firebox under the oven which lets air into the oven through a slot in the back of the oven. I have found that the extra air makes starting a fire much easier and saves about half an hour in getting the oven up to about 1,000 degrees F. At that temperature I have found that the extra air is too much and keeps the oven from getting hotter. I close the lower firebox door and make sure the oven door/plug is in place and the oven temperature shoots up to 1,200 degrees F in a few minutes.
Next we tried it with a couple of ovens at Superior Clay. Similarly, the extra air, supplied through a regular Vestal firebox combustion air spinner, got the fires going faster but needed to be closed down in the final run up to 1,200 deg. F.
Unfortunately Vestal no longer makes that spinner so Superior Clay is making them.
Meanwhile, the next oven we built we constructed a simple brick-sized hole in the back of the oven which could be closed off by shoving a brick in the hole. By cutting the brick into a wedge we could adjust the amount of extra air.
Okay, our ovens are well designed and work perfectly well without any extra air, Jerry, but now we recommend extra air to provide more control and make the fires easier to start and regulate.