New to rocket stoves.

Planning my first rocket stove and trying to decide between L style or J style or K style any advice would be appreciated. Also curious how much difference it makes to have a round pipe vs square pipe.

Hi Joe;  
Welcome to Permies! And Welcome to the wonderful world of rocket science!

To start, use a square feed tube and burn tunnel.  The riser can be either.
Round is not beneficial until the riser.  Even the riser can be square if it is more convenient

So a J tube is a true self-feeding rocket stove, with it you get up to 45 minutes of burn. This is my choice.

An L tube is just a hand-fed chimney,  they burn great but you keep it going all the time by hand.

A k tube is the last choice, they do work, but after it heats up it is generally trying to burn backward up the feed tube.

Are you building a rocket to cook with?
Or are you thinking of a mass heater?
Or are you just playing (experimenting)?

thomas rubino wrote:Hi Joe;  
Welcome to Permies! And Welcome to the wonderful world of rocket science!

To start, use a square feed tube and burn tunnel.  The riser can be either.
Round is not beneficial until the riser.  Even the riser can be square if it is more convenient

So a J tube is a true self-feeding rocket stove, with it you get up to 45 minutes of burn. This is my choice.

An L tube is just a hand-fed chimney,  they burn great but you keep it going all the time by hand.

A k tube is the last choice, they do work, but after it heats up it is generally trying to burn backward up the feed tube.

Are you building a rocket to cook with?
Or are you thinking of a mass heater?
Or are you just playing (experimenting)?

Thank you thomas that was very helpful. I'm making my first one for cooking and playing.

Are you planning on making an all metal J tube?

Fox James wrote:Are you planning on making an all metal J tube?

I was.....is that a bad idea?

Hi Joe;
In truth, there is nothing "wrong" about building with metal.
Metal will spall with the heat and warp. It will have a limited life.
Very common to see youtube built metal rockets.  They rarely show them after a season of burning.
Solid red clay bricks and "mud" are the recommended building material, you will not spall or warp a clay brick...

If you have the extra metal and a welder, but you do not have any clay bricks (home depot)  then go ahead and play with metal.
After you see and hear a rocket take off... Well, most likely you'll go and find some bricks...

There are some issues with using metal but a lot depends on your goals and exactly what you want to the stove for and how often you intend to use it?.

I have built L-tube rockets for cooking (an oven and two maple syrup evaporators). With a long enough horizontal feed (around 30") they burn great and hold enough fuel to last a good while between loadings. Mine are between a 6"w x 9"h feed and 6" diameter riser, and an 8" x 9" feed and 8" square riser. Both are very efficient and put out a lot of heat and zero smoke after a few minutes.

Going with much smaller dimensions for cooking small quantities would still work, but you need the length for the fire to burn fully. I wouldn't use less than about 24" for both feed and riser.

I really don't like the K style as it is asking for the fire to smoke back and any irregularity in the wood will tend to hang up and not feed the fire. I don't understand why so many people build them when they require coping mechanisms (lids and flaps) to correct some of their flaws.

Glenn Herbert wrote:I have built L-tube rockets for cooking (an oven and two maple syrup evaporators). With a long enough horizontal feed (around 30") they burn great and hold enough fuel to last a good while between loadings. Mine are between a 6"w x 9"h feed and 6" diameter riser, and an 8" x 9" feed and 8" square riser. Both are very efficient and put out a lot of heat and zero smoke after a few minutes.

Going with much smaller dimensions for cooking small quantities would still work, but you need the length for the fire to burn fully. I wouldn't use less than about 24" for both feed and riser.

I really don't like the K style as it is asking for the fire to smoke back and any irregularity in the wood will tend to hang up and not feed the fire. I don't understand why so many people build them when they require coping mechanisms (lids and flaps) to correct some of their flaws.

Well I started welding a j tube together and I wanted it to be kind of portable so I went pretty small. I tried to do the 1 2 4 ratio but i think i made the flame tube too long and maybe the feed tube could have been longer and the riser longer as well. I went with 5 10 20 but i think my flame tube is long because i didn't count the with of of the feed tube and the riser. We'll see how it works soon though, I'm having fun anyway. I'm planning to add a few finishing touches but here it is so far.

Fox James wrote:There are some issues with using metal but a lot depends on your goals and exactly what you want to the stove for and how often you intend to use it?.

Mostly just having fun building and burning. Probably cook some and I can always make more and in different ways.

That feed tube is not tall enough to keep fuel upright and contain any reasonable length sticks. You would want at least 12" height from floor to top. Having the burn tunnel (the standard term for "flame tube") 1.5 times the full feed tube from front to back, and the riser 3 times the feed, would be good proportions.

What size is the tube? 4" square? Riser height?

Glenn Herbert wrote:That feed tube is not tall enough to keep fuel upright and contain any reasonable length sticks. You would want at least 12" height from floor to top. Having the burn tunnel (the standard term for "flame tube") 1.5 times the full feed tube from front to back, and the riser 3 times the feed, would be good proportions.
What size is the tube? 4" square? Riser height?

Yeah it seems the feed tube may be too short but that's easy enough to remedy. 6 inch feed tube 10 inch burn tunnel 18 inch riser. 4 inch square tube. I've seen some people put extra holes and tubes in the riser to add air flow there, any thought on that?

Add 6" to both the feed and riser and I think this will work okay. A drawback of a smaller than 6" size is that it is hard to get in to clean out ash. A properly functioning J-tube will leave very little ash and no coals at all, but you will eventually need to clean it. Just tipping upside down may be feasible in your case. Something heavy or bulky or especially built in place will need a cleanout access at the base of the feed tube.

Adding extra air at the riser except in skillfully engineered ways is likely to hurt your performance. At this size, I think you will be much better off with a simple system. The most common issue is too much air rather than too little.

Glenn Herbert wrote:Add 6" to both the feed and riser and I think this will work okay. A drawback of a smaller than 6" size is that it is hard to get in to clean out ash. A properly functioning J-tube will leave very little ash and no coals at all, but you will eventually need to clean it. Just tipping upside down may be feasible in your case. Something heavy or bulky or especially built in place will need a cleanout access at the base of the feed tube.

Actually it worked great I can't attach a video but it was awesome just the way it was.

Glenn Herbert wrote:Adding extra air at the riser except in skillfully engineered ways is likely to hurt your performance. At this size, I think you will be much better off with a simple system. The most common issue is too much air rather than too little.

Yeah it worked great just how it was. I can't attach a video but here's the final product.