Rocket stove heat riser location

Hello, I am building a rocket stove and I was wondering shoud the heat riser be in the center of the tank ? I couldn't find any information will there be a problem if the heat riser is offset from the tank ?

Welcome to Permies, Ivan! The heat riser in a rocket mass heater does not have to be centered in the barrel, but you should have at least an inch of clearance all around, two is better. Which side will you have the manifold on? The transition from barrel to duct or whatever you will have is important and is a choke point if you do not make it big enough for free airflow. The more space between riser and barrel on that side, the better, and the exit from the barrel should be distinctly larger than the rest of the duct. If you have a 6" system size, make the barrel exit 8" diameter, or even 10" if there is less than around 3" of clearance between riser and barrel.

Hi, thank you for the reply I took pictures with the measurements. The sizes will be in the pictures

Hi Ivan;
Your measurement's all look good except your transition exhaust outlet.  
4.7" is not nearly large enough
Make it 6" minimum, or  better to make it 8".

Ivan, it looks like you have a piece of steel stove pipe inside your insulated riser. This is doomed to fail, the steel will be corroding like mad in a high-temperature and oxygen-rich environment.

Peter van den Berg
The metal in the middle was just for the perlite mixture, I will try to make the exhaust bigger then ty all !

Where your outer tank is cut open for the transition to the thermal mass, if you are using a 13cm pipe, try cutting the tank opening larger, say 20cm diameter, and then taper that transition down to the 13cm pipe over say 10cm+. That will help improve flow around that bend. If you can shift the riser a little away from that transition as well that would be ideal.

If you can remove the metal inside the riser that would be best, as the metal can spall in a way that can cause a near or total blockage of the exhaust once it starts failing. Then you will have to take it apart to clear out the blockage when you need it to heat. Perhaps a metal grinder would fit in there where you can cut it into quarters lengthwise?