Hi, I'm slowly gathering materials for a rocket stove mass heater and am having trouble sourcing the horizontal ducting at a reasonable price. I've tried local scrap places but they don't seem to have solid flue liner. New prices are seemingly prohibitive for the long lengths required. I have been trying to search for any examples of using flexible steel flue liner as a cheaper new alternative but I haven't had much luck. I'm wondering whether the potential draw back would be in internal surface not being smooth and restricting the flow?
Does anyone have any experience of using flexible flue liner for this purpose? I'd be really interested to hear your views on this.