I’ve got an observation/question. Won’t you have less problems with creosote in your heat exchanger if you create a gap between the burn chamber and the heat riser, to introduce some fresh oxygen so all those nice hot gasses can combust? That’s the feeling I’m getting when I’m looking at your setup. There’s a lot of heat, but also a lot of unburnt gasses (that creosote is just unburnt fuel) and if you introduce some oxygen at that point, I reckon you’ll get an ever bigger heat return, and in the long run less problems with the creosote.