Air space between the first course cinder block in the fire box area

[Swingpure]

For a cinder block evaporator, is there any value and having like a 1/4” air space between the cinder blocks on the first course in the fire box area to allow for some additional air flow other than what comes in from the entrance of the firebox?

Thank you.

[SeanD]

Any additional air will have a bigger effect on your boil/fire than any heat loss from a small gap will, based on my experience boiling on a block arch. You'll have a clean-burning, hot fire in the first hour or two almost no matter what you do. When hour 10 comes along and the bottom of your fire box and air intakes are filling with ash, that's when you really want that fire to keep going strong. Air is the most important part of that.