Rocket stoves: J profile or L profile?

I'm planning to build rocket stoves for a couple of applications - a cook stove and bathroom water heater - and I've spent a while looking at designs: Larry Winiarski's, Ianto and Linda Evans's, their various offshoots, plus all manner of other stuff on the web. I get the impression designs have gone in two separate directions centered around either the J profile or L profile fuel feed tube and there doesn't seem much crossover between. At the moment I'm thinking the L profile might suit my cook stove application better while a J profile would work better for the water heater, but I'd really love to hear from people who have experience of building/using either/both about the pros and cons of each.

Wendy Howard wrote:
I'm planning to build rocket stoves for a couple of applications - a cook stove and bathroom water heater - and I've spent a while looking at designs: Larry Winiarski's, Ianto and Linda Evans's, their various offshoots, plus all manner of other stuff on the web. I get the impression designs have gone in two separate directions centered around either the J profile or L profile fuel feed tube and there doesn't seem much crossover between. At the moment I'm thinking the L profile might suit my cook stove application better while a J profile would work better for the water heater, but I'd really love to hear from people who have experience of building/using either/both about the pros and cons of each.

The advantage of the J is self feeding. The wood falls as it burns and so more wood can be set and left. This is good for a mass heater as the burn cycle takes a long steady burn. the L shape requires more tending but gives better control for short term uses like cooking where the idea is to save on wood and smoke.... and just get the job done and no more. With a heater, a little more heat into the mass just means it will last a bit longer.

Thats what I see anyway.

A potential cross-over could be build in both the J and L into the same pipe.

Allow for the top of the "J" to be capped after inserting wood. 
Once cap is in place, the air draw would be forced to come from end of "L"

I would presume this would offer best of both worlds- wood would gravity feed needing less attention, with little to no danger of fire creeping up sticks and smoking room.

And I see your post count is "one" Wendy - so welcome to the forums! 

I've only reciently discovered this place, and love it : it's filled with so many gifted and generious (with time and knowledge) people. 

& keep us up to date on your projects, I'm personally very interested in cookstoves.

Scott911 wrote:
A potential cross-over could be build in both the J and L into the same pipe.

Allow for the top of the "J" to be capped after inserting wood. 
Once cap is in place, the air draw would be forced to come from end of "L"

I would presume this would offer best of both worlds- wood would gravity feed needing less attention, with little to no danger of fire creeping up sticks and smoking room.

Interesting idea! But feeding fuel into the J profile stoves appears to involve having a fair bit of the wood sticking out of the feed tube - at least until it burns down a way - so it would presumably require more of a U profile in order to provide a long enough feed tube to be able to cap it?

I'm still thinking the L-profile works best for a cookstove. A few reasons -

[li]No horizontal space is lost accommodating the feed tube, and generally a more streamlined design which is easier to work with/around[/li]
[li]No smoke escape during start-up[/li]
[li]No particular benefit from having the self-feeding advantage of the J-profile since the stove will be fairly constantly attended while in use (it will be used in combination with a hay-box for longer cooking times and won't have an oven)[/li]

And conversely with a bathroom water heater, there doesn't seem to be a huge advantage in the L-profile. Though if smoke escape IS a regular feature with the J-profile, then maybe this is where your hybrid idea could be useful? Anybody with experience of a J-profile stove care to comment?

Thanks for the welcome! I quite often come to these forums to read up on stuff, but it's a measure of the quality of the discussions here that I haven't found the need to post a question before.

I would very much like to hear about a j-tube cook stove in action.

I mocked up a j tube with some triple wall stove pipe and cooked some marshmallows over it a couple days ago, I think I've got a video, so I'll try and figure the utube thing out tommorow