Hi, looking to install a stove on my boat which means cutting a 6+ inch hole in the roof for the flue (4inch twinwall ??) and chimney. My boat is just over 2 years old and has diesel blown air heating which is OK but doesn't cope too well when really cold. I am not a liveaboard so am doing this mainly as a project and will not be dependent on the stove as permanent heat source. I feel OK with insulating around the stove etc but am struggling to understand the dynamics re flue, chimney etc. My stove (Hamlet Hardy 4) has a 4inch opening at the top. After a lot of searching on the internet, Youtube, forums etc it seems the traditional approach is to use flue which goes into a cast iron deck plate bolted and sealed on the roof with a removeable chimney on top of the plate. Recent regulations seem to indicate that twin wall flue has to be used. Is it possible for me to do the following ? Can I use 4inch twin wall attached to the stove by an adapter which exits the roof about 100mm above a Dektite heat proof roof flashing then attach to that a 500mm length of 4inch twin wall (+ cowl) secured by a locking band as a chimney ? Could this work as a removeable chimney ? or is it not possible to undo the locking band once fitted ? I would protect the ceiling internally with a firestop collar and pack around the flue inside the roof space with fire rope or similar. So, what I really need to know - is 4inch twin wall too small ? If so, what is the minimum I can use safely on a boat. I cannot find anywhere where minimum flue size is mentioned. And, more importantantly, is what I want to do possible, or is there a reason why a cast iron deck plate has to be used rather than a Dektite, and, would what I want to do work and pass a BSS ?. All comments/advice welcome - thanks Phil