Math As Easy As 1 – 2 – 3
The math that drives the physics of the “Rocket” is fairly straight forward. The length of the roof of the Burn Tunnel must be at least two times (2x) the diameter of the cross section. So, for a 200mm / 8in system, the roof of the Burn Tunnel must be 400mm or 16in, at least.
The height of the Heat Riser, measured from the roof of the Burn Tunnel, must be the three times (3x) the diameter of the cross section. So, for a 200mm / 8in system, the height of the Heat Riser, measured from the roof of the Burn Tunnel, must be 600mm or 24in, at least.
There are some “math reasons” why you should not exceed 3x the cross section for the roof of the Burn Tunnel. In my design, I aimed for a Burn Tunnel roof length of 2.2x and it works well.
If you want to “go big” somewhere, the place to do that is the height of the Heat Riser. The taller it is, the faster and hotter the Rocket will run. Just keep in mind that you will need to find something to put over it, one way or another, as the Barrel Cover.
The chart below provides a fast, simple look-up for the measurements of your system:
Inch & MM Sizes for Rocket Mass Heaters
Woof. Ok, this post is waaaaaay longer than I had expected it to be. Hopefully you are still with me, and better yet, some of this was valuable to you.
In my next post, I’ll talk about my first and subsequent testing burns that I have done with the “Version 2” system and a few surprises I have learned along the way.
After that, I will talk about how I run my Rocket Mass Heater system in my greenhouse, including lighting, feeding and cleaning.
If that doesn’t prove to be another TL;DR bait, I’ll finish up with a review of what I’m coming to recognize as “normal behaviours” in temperature and a bit of a snark about Rocket Mass Heater systems are and are not.
If you have any constructive comments, questions or suggestions, please leave them in the comments section below this post. I would absolutely love to hear from you! I hope this series of posts helps someone else get into this fascinating technology.
Woaw! That was an amazing post! Clear, simple and to the point. Thank you very much. I feel a lot more comfortable with the terminology and theory of the rocket mass heater. Cheers!
Hi there, Viviane! I’m glad that it was helpful. Are you thinking about building one, or just fascinated with the whole idea?
Brilliant, informative reference reading i will come back to again and again. Will also point other in your aricles direction, thank you for the sharing of knowledge.
Hi there, Barry! Thanks so much for the glowing feedback. I’m glad you found the information helpful. Do you have an RMH of your own, or are you considering building one?
excellent blog and thank you.
You’re very welcome, Ray! Thanks very much for the note, it is very much appreciated.