hi guys i posted the other day in reverse flow my mistake so i wuill re introduce myself. my name is dean and i live in quebec canada. i am in the middle of building a small sfb smoker. it is my first build and i have never actually seen a smoker up close s i am going completely from what i read on line. i am a mechanic by trade and am building the smoker from all recycled material. the firebox is a old bbq propane tank, the smoker is a old compressor tank" 44 around and about 3 feet long" the smoker hingesare from a honda civic tailgate the firebox hinges are from a civik hood. the chimney is a p/t cryiser exhaust. asnd so on. my main question is how big should the hole be between the firebox and the smoker? and how important is the length of the chimney?