Not enough heat

My RMH isn't getting hot enough to burn the smoke off. Any ideas. Thank you.

Welcome to the permies forum Mike.
You have a rather cool and simple looking design. I hope you don't expect much heat output from it though.

Well, I'm not sure where to start. Really need some more details. It looks like you have a 4.5" core, but the duct looks like 6". But right off I see no 4th side (next to barrel) for the feed tube. General dimensions of the "J" look workable.

Did you do a test burn with no barrel? What is the barrel gap from top of riser? When you say it's not hot, do you have a temp reading? Does it seem to draw weak (smoke back) at the feed tube? Is the final exhaust smokey or clean?
I can help solve your problem, but need more info.

The core is 4" and I did a test burn without the barrel. It had good draw. The gap at the top of the core to the barrel is 1.5". The top of the feed tube is missing the top brick. I am planning on filling the gap with cob after I wrap the barrel in copper tube to make a heat exchanger. It appears that the barrel and the start of the 6" exhaust tube get hot, but the mass isn't. I will get temps for my next reply. Thank you

Sorry, I forgot to add that the exhaust is smokey.

i can only guess, since im a newbie, but id say your (1-1/2) gap is too small at riser top.

ronald bush wrote:i can only guess, since im a newbie, but id say your (1-1/2) gap is too small at riser top.

Yep, i'd put a 2 inch gap at least. this can't harm anything.

How old is your mass? If still fresh, it won't heat up untill completely dry.

Plus, don't expect much heat from a 4 incher, theses are temperamental animals.

There's way too much mass in the j-tube, the wall thickness should be scaled down as well. At least half of what you are using now, the ratio of cross section area and wall thickness is too unfavorable at the moment. And what type of insulation did you add around the completed j-tube? Sand and dirt won't work, cob or hard firebrick isn't insulating either.

In the transition from barrel to bench channel it's easy to create a restriction even when it won't look like that. Max is right about the 4" RMH being a bit finicky, not easy to get it right.

Thank you everyone for your help. I will do what I can to correct the situation.