RMH troubleshooting

Hello guys.

I'm from Slovenia, and in last few weeks we build RMH in our workshop. We used a 6'' system and build everything by the book (Evans and Jackson). Yesterday we've fired it up for the first time. For now everything is looking good. Draft is exellent, exit fumes aren't hot (i can put my hand over the smoke), the place is getting warmer, but here's the problem. I thing it's not getting warm enough. Outside of insulated burning tunnel is hot, heat exchange barrel also (if i pour water on top, it evaporates instantly), but the chimney pipes in the thermal battery (bench) are just warm, I didn't mesured the temperature yet, but I can place my hands directly on pipes (the bench is not finished yet), so I would say its about 20-30 degrees C (68-86 degrees F) maybe a little bit more. I think it should be warmer. Am I wrong?

What temperature did you achieve in/on your bench?

Thank you very much in advance.

Greetings from Slovenia

Ales Zorko : I am really just guessing, before we condemn the Transitional Area as being to small, lets look at other areas. If you are sure that you have a minimum Gap of
3.75 cm or 1.5 inches between the top of the Heat Riser and the inside Top of the barrel, and you have never heard the Top of the Barrel make a single loud 'ptong sound' as the
barrel top 'oil cans' between convex and concave,or heard it make that sound as it cools down, and you have as loud a rocket sound as when you tested your R.M.H.outdoors
without the barrel, then we look at some more unlikely places.

How did you determine that your Heat Riser was Plumb and level, also how did you determine that the barrel was Plumb and level !? Did you wrap your insulation material around the
Heat riser to have a minimum gap between the Heat Riser and the inside of the barrel of 2 inches or 5.0 cm everywhere?,

Is the barrel exactly centered over the Center of the Heat Riser ?! In my copy of 'The Book' on page 24 they talk about off-setting the barrel to one side to protect close flammable
exposures, there is a sketch also! If you have a spot right at the Transitional Area where the hot exhaust gases Fall vertically down the inside of the barrel, then ether a small bulge in
the insulation, or a small off-set in the barrel away from the transitional area, or a merely adequate Cross Sectional Area at the point were the exhaust gas turns 90 degrees to flow
horizontally, and/or rough side walls or a large piece of plaster/Cob fell into the path of the exhaust gases, any of these slight deviations from perfect, especially when combined with
others, will slightly choke off good gas flow and reduce performance !

If the barrel has to be off-set, then the whole internal structure of your Rocket Mass Heater R.M.H., should be re- worked so that the wide spot is directly over the Transitional Area!

Check out these things, getting a simple agreement that you are correct, and see if you can reshape the Cob to gently direct your hot exhaust gases through the Transitional Area
past smooth walls, your finest work should go into this area. Though it was not specifically mentioned, you should also have a Ash Pit and a "T" fitting for your First Clean Out, and
inspection point,

Because I was trying to be very thorough, I remembered to ask you to check that you don't have any unsealed sections of stove pipe or loose Caps on your Clean Outs, I always tell
people to hide their Clean Outs, the monkey in all of us must explore whats behind that cap ! You can and should paint a clay slip seal over every seam and connection, any brake
in the seal will show as flacked off areas of clay slip.

Wet Clay Slip reapplied before the Cob is spread on, will improve the material bond between the Cob And the Stovepipe ! Try these few simple steps and come back here to Permies
24 / 7, with over 19,000 members world wide you should get a timely answer ! For the Good of the Craft !

Think like Fire, Flow like a Gas, Don't be the Marshmallow ! As always, your comments and questions are solicited and are Welcome ! PYRO - Logically Big AL !

@Ales,
Your stove is drafting well, the barrel gets really hot. But the bench isn't finished yet, it's bare stovepipe only. There's one thing with stovepipe compared to a full cob bench: it sheds heat much more quickly. Probably there will be quite some condensation fluid in the pipes as well.

When the bench is finished, the pipes will run hotter because of the slower extraction of heat. At first, there will be no warmth from the bench at all because the thing is wet plus a lot of water in the pipes. All this will solve itself in a matter of time while you fire your stove. So finish your bench and enjoy!