possible shelf sealing RMH outlet.

This is combing thinking from 3 sources.  1.  Self stopping folded path solar collector design.  2.  Discussions of cold plug on mass heater start up.  3. And the video including the discussion of the RMH with too much draw.  Don't know if this will work or not?

Can we make a chimney that does cold plug to shut itself off without draining heat from the mass?   The folded path solar collectors take advantage of having the inlet and outlet at the same height and insulation in the right places to do what amounts to a cold plug stood vertically.  The you(won't let me use character) facing down fills with cold air as the burn comes to an end while the you(same problem) facing up stays filled with warm air/smoke from the shut down to start with and then maintains the warm side of the plug from heat conducted by the uninsulated first riser pipe.  The insulation around the downward one keeps it from conducting cold into the room.  Would stacking a cold plug and a warm plug stop flow in the pipe?  Probably ideally this would have wall jack outlet slightly lower than the top of the upward aimed you(letter) so you could have both plugs fully active.  Picture is the pipes laid out flat but probably you would want them in a triangle with just enough room for the by pass door/damper.  On start up you would open the door so the smoke bypassed both plug locations.  Once it was hot it close the door.  This would add a bit of drag to the system  going around 2 complete reversals of direction plus 2 extra straight runs which is why added draw would be wanted.  To automate this what if a bi-metal spring latch was added to the uninsulated riser pipe.  When that pipe gets hot enough for the latch to trip, the damper is weighted to close.  That would give a time delay while things got started and add the flow restriction only after things get rolling good.  If mounted close to the barrel the uninsulated pipe would be heated by the barrel to aid in start up and towards the end just a bit to help keep it flowing.  Ideally the door/damper should seal well and be somewhat insulated.  The stacked plugs combined with inlet and outlet heights the same in the top of the wall greatly reduces back siphon.