Long story short: got a new roaster, it requires Category III (positive pressure) venting. The roaster itself has the fans. It seems no one in El Salvador has heard of these categories as people don't have chimneys here 😅 so your regular hvac guy knows a ton about AC but not much about the HV part.

Can I just use a stainless steel 16 gauge pipe? The gauge even seems to be overkill for this but it's the size that's readily available on the diameter of the tube. The coffee internet seems to be adamant that the manufacturers actual requirements need to be followed but living here in the third world that's sometimes hard. To quote that guy from the Apollo 13 movie "I don't care what it was designed to do, I care about what it can do!" But at the same time I don't want to be stupid. Worst comes to worst I can import it, but it's an expensive piece of pipe and want to see if I can save a couple million sats by doing it locally