i have some experience. i think @roya ୨୧ does too.

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

im curious, what does the manufacturer recommend?

Category 3 is an insulated, multi layer pipe. the whole point is to prevent burning materials in direct contact with the pipe, like roofs or walls. Generally you also want a 1" gap between the pipe and surrounding materials. Your pipe idea shoukd work fine, so long as the pipe does not come into contact with flammable materials.

did you get that figured out?

It'll be fine lol hopefully

just remember what i explained earlier. its all about not starting a fire by the hot exhaust pipe being in contact with flammable wall/roof material. if you insulate that pipe from rhe flammable materials, it should be fine, and thats whay the proper pipe does inherently.

Yeah it's all concrete here anyways so it's less of a concern The ceiling there and all walls are just concrete

if thats the case its basically no concern. nice!

looks fine to me, especially if it’s surrounded by concrete

Whats the question?