Cheap Rocket & Five minute riser

Before making RMH for our new bunker building, we would like to test the concept in our old log house, build our first one. As here in Arctic Circle next to Russian border  there are no Home Depots around, ceramic fibre boards, chimney pipes etc. way too expensive transport, we want to make it from basic stuff with basic tools. So our first thought was 8" J with 5 minute riser +bell bench +our 100 years old tile chimney.

Anyone done bigger/8" five minute risers? Meaning 10" pipe +25mm Insulfrax LTX for 8" system? (Insulfrax is our only option here) How did it work? Did you/does it change any other dimensions? Is it worth to make riser a bit taller?

For our old log house there is simply no other way than to make RMH on wooden floor so 5 minute riser will save significant amount of weight compared to tiles and has better shape for vortex (+it is way cheaper and faster to make).

Anyone done simple "floor channels" (Batch rocket/Peter van den Berg) for J? Made the back corner of burn tunnel more round? Any other optimization tips? Thanks!

A basic configuration  8” J tube is a powerful heater, a 5 min riser is very effective, it is just the feed tube that needs to be robust and made from a hard wearing material.
The main issue with any size J tube is the fact you need to feed the fire every 20 minutes or so bit they do work very well and are fairly easy to build.
This is a very good thread to read …..  https://permies.com/t/122458/Advice-RMH-build-Hokkaido-Japan

Thanks Fox!