First attempt welding a rocket stove.

After seeing the prices of rocket stoves being $130-$800 on etsy, I decided to attempt at making a rocket stove from scrap metal.  The total cost in metal is roughly around $20-$30 depending on which metal shop you buy from.

I didn't follow any plans, kind of went based on a couple images of what I saw online.  Some things that I'm planning to change:
1) Adding top hinge door to the feed chute.
2) Considering shortening the feed chute
3) Grind down welds to give better look



Any feedback, critique or recommendations is highly appreciated.

Nice construction work. Is this a 4" square system? The feed tube is much too tall relative to the riser, so that it may be difficult to establish strong draft in the right direction. I think a 16" or so long feed would be better. How tall exactly is the riser? A general rule of thumb for rocket mass heater J-tubes is 1:2:4 or 1:1.5:3 for feed tube, burn tunnel and heat riser. A 16" feed would give at least a 48" riser. You are missing the burn tunnel entirely as is typical with K-style rocket stoves.

A major factor in effective combustion is to keep the fire as hot as possible until it has finished burning, and only then allow the heat out to do work. If you let the whole combustion core shed heat to the air, the fire will never get really hot, especially in a small system like this. You need plenty of insulation to keep the flame hot all the way to the exhaust.

You mention a cap on the feed tube; I hope you have put a cap on the bottom leg, cleanout or air supply or whatever you intended it to be. Too much air can dilute the heat and reduce the effectiveness of combustion.

Three "T"s of combustion: time, temperature and turbulence. The fuel gases need to stay hot enough for long enough and have enough turbulence for good mixture. Insulation will help temperature. The "V" flame path is not likely to give the gases enough time to finish burning or turbulence for thorough mixing. If flame comes out the top, you are wasting fuel. Most of the fire is in the riser, with not much to make turbulence. If you must use the sloped feed, at least connect it to the bottom leg rather than the riser so there are direction changes in the flame path to give turbulence and more length for dwell time.

Glenn Herbert wrote:Nice construction work. Is this a 4" square system? The feed tube is much too tall relative to the riser, so that it may be difficult to establish strong draft in the right direction. I think a 16" or so long feed would be better. How tall exactly is the riser? A general rule of thumb for rocket mass heater J-tubes is 1:2:4 or 1:1.5:3 for feed tube, burn tunnel and heat riser. A 16" feed would give at least a 48" riser. You are missing the burn tunnel entirely as is typical with K-style rocket stoves.

A major factor in effective combustion is to keep the fire as hot as possible until it has finished burning, and only then allow the heat out to do work. If you let the whole combustion core shed heat to the air, the fire will never get really hot, especially in a small system like this. You need plenty of insulation to keep the flame hot all the way to the exhaust.

You mention a cap on the feed tube; I hope you have put a cap on the bottom leg, cleanout or air supply or whatever you intended it to be. Too much air can dilute the heat and reduce the effectiveness of combustion.

Three "T"s of combustion: time, temperature and turbulence. The fuel gases need to stay hot enough for long enough and have enough turbulence for good mixture. Insulation will help temperature. The "V" flame path is not likely to give the gases enough time to finish burning or turbulence for thorough mixing. If flame comes out the top, you are wasting fuel. Most of the fire is in the riser, with not much to make turbulence. If you must use the sloped feed, at least connect it to the bottom leg rather than the riser so there are direction changes in the flame path to give turbulence and more length for dwell time.

Thank you for the response! After reviewing more photos based on your comment about the slope connection being wrong, I see what you mean regarding the wrong connection point.  I'll look into ways to improve this based on the things you mentioned including fixing the lengths.

If you want the 45 degree feed, you could flip the whole setup around so what is now the riser lays horizontal, cut off the end of that, and weld it to the top of the new riser making it taller with the pot supports on top. Relocating the angle feet should not be too hard.

What size is the square tube, 4" or 3"?