maximum height for Rocket Mass Heater riser?

my impression is that, generally speaking, a taller riser is better. but I imagine there's a point at which this is no longer true.

so, supposing the riser is well insulated, at what point does making it taller stop increasing performance?

sounds like an experiment waiting to be done by you . I can't remember if it was on this site or another but 3:1 (rise over run) was better than 2:1 and 2.5:1, so I guess your starting point can be from there.

current project is close to 4:1. seems to be working well, but I didn't try any other arrangements. that probably doesn't add much to the stove discussion, but it's one data point anyway.

unfortunately, I don't have a lot of material around for experimenting. or time. maybe someday.