Influence of barrel on draft in a rocket mass heater

Hi,

We follow the book on rmh (Ianto Evans, Leslie Jackson) and we found that our all brick rocket spits fire like a dragon, by itself, even without insulation and being completely sealed.
When we place the barrel, however, the draft and fierce decrease noticeably. It keeps burning, but the flames tend to go up in the feeder.
Is this a normal observation? We've tried different heights in barrel placement, but we keep seeing that the force of pulling in the air somewhat decreases.

Any insights, shared experiences, etc. very welcome.

Jasper and Sijmen

Sijmen; When you place the barrel on, you must have a chimney up at the far end of your mass. Is this a practice build outdoors ? If it is, then don't worry about the decrease in draft. When you have your horizontal run in mass with a vertical chimney at the end it ,if you have carefully followed building dimensions... then your dragon will roar again! Give more information and post photos of your build as you go.

Thomas R. : I second your observation, I just would initially place the Vertical chimney immediately after the barrel! It is a good final check, and can tell me if I have
any problems I Know it must be in the Rocket Mass Heater RMH, the Barrel, or the Transitional area and not in the Piping of the thermal mass.

Though I probably would not bother at all with this step on a RMH that was clearly working as well as this one.

For the Good of the craft Big AL !

Thank you all so much, it was indeed the right vertical flue that brought the dragon back to life!
Pfff, no more rework

Yes, I had a similar experience the other day with an outdoor test build. Put the barrel on and packed sand around it for a seal and got smoke out of both the feed tube and double-elbow that I was using for the exhaust. But as soon as I added a 5-foot section of pipe on top of that double-elbow, it started drafting properly.

It can be fun seeing physics at work!

Yep, and that's the proof that the barrel adding to the draft is a myth!

Umm... I beg to differ. Obviously putting a restriction over a free updraft is going to reduce the draft, but an RMH system never has a free updraft. The point at issue is whether the barrel *in a system* contributes to the draft, all other things being equal. The best test of that is insulating the barrel and seeing what effect it has - the flue gases have to be directed back down to floor level no matter what kind of device does it. Reports of people cobbing over whole barrels and losing some draft are suggestive of a real effect. It would be good to see this put to a specific test.