Yes I was clear on some air is needed to sustain the smoke flow and combustion of the smoldering pellets. I'm planning on using one of Todd's AMNPS in the build for the smoke source if I ever get my design finalized in my head. I'm familiar with the need for some sort of fresh air intake and exhaust for that to work. The desire to use an AMNPS is one reason I'm asking this question as I'm thinking the constant airflow movement from a re-circulation blower will decrease the burn time on the AMNPS as it would be like "fanning" or constantly blowing the smoldering pellets making them burn much faster. Another question I would have with a re-circulation if is does the smoke build up on the fan shaft and eventually gum up the bearings? Smoke "seasoning" seems to coat pretty much everything inside every smoker I've ever seen. I would plan on doing "hot" smokes as well (225 to 250 range).
I have seen several metal cabinet builds on here (converted food warmers) where they used a high temp squirrel cage blower to constantly move air over the finned elements. Walleye1's build is one I can think of off the top of my head. I just was not sure if this was a must have to keep the heating element from burning up or just something the builder decided to do.
Here is a few of his photos with what I'm talking about. In the first one the blower and return duct are on the lower left of the side of the cabinet. The 2nd photo is of the inside showing the air intake to the fan and the return over the finned elements. Of course he used a Bradley puck smoker for his build so the smoldering pucks are somewhat shielded from the fan air flow.
And to Walleye1 if you read this, that is one sweet build you did.