Big day! The rocket straw badge!
I've built a J-tube style RMH:
and heated a space with it for 1 week: https://permies.com/wiki/125877/pep-rocket/Heat-Space-RMH-Week-PEP#2873101 that's all the requirements for this aspect.
Thank you for your help, Staff!
I never could have done this without help. Thank you to Alex, Jeff, and other wonderful rocket scientists at permies!