Secondary air for L-shaped rocket stove

Hi Permies!

First off, love the site!  Such a great resource with so much information.  That said, I am sure my questions have been addressed but there is so much information on this site and some of it is conflicting and dated so it's quite difficult to know what the best standards are at this moment.

I am in the process of designing and building an outdoor, wood burning cooktop stove.  Here in Brazil, these are quite common but almost exclusively just a standard cooktop with fire burning underneath.  I am going to build an L-shaped rocket stove (I considered the j-style tube but I wasn't certain if I would need a tall riser, following the 1:2:3 ratios I am often reading about on here and as this is exclusively for cooking, I want my final height at a comfortable 36".)  I've seen quite a few nice L-shaped designs.  They all have some sort of secondary air coming in through the same feeding area for fuel, often with a grill to create seperation.  I've read and watched the walker stove videos and seen others discussing secondary air.  It seems to be the standard to have a feed running through the front that allows the fuel to heat the air passage which helps with the mixing.  

My question is how crucial is having the air enter through the front? Can I have secondary air entering from the back or side and achieve nearly the same effect? I hope this makes sense.  If not, I can draw something out.

My second question is that I see most cooktops are refurbed ceramic glass tops.  This is not an option for me as cook stoves here are all gas.  My concern with cast iron tops is if the quality isn't great, I may experience warping from extreme heat.  Has anyone tried granite cook tops? Granite is much more accessible for me.  

Thanks for the time and thanks for the great resource!

I think you should look at a J tube, much easier to operate and feed while cooking.
I think my J tube stands at 42” high

If you are making a permanent installation outdoors, or can sink part of the core below floor level, a J-tube would work excellently for a cookstove. An L-tube would require bending down to check the fire and feed it unless the top is higher than you would want.


Granite would crack very quickly from the extreme concentrated heat. It can stand a lot of heat, but not uneven heat.

Art Vandelay wrote:Hi Permies!
 

My second question is that I see most cooktops are refurbed ceramic glass tops.  This is not an option for me as cook stoves here are all gas.  My concern with cast iron tops is if the quality isn't great, I may experience warping from extreme heat.  Has anyone tried granite cook tops? Granite is much more accessible for me.  

I sure like what Fox James has done with a steel top, Is that an option for you.  Even if a granite top would work, (and it really wouldn't very well with the later mentioned cracking from uneven expansion) it would be very hard to make it to have a perfect fit.  Far easier with the steel top (and better)  And many ways to get this circle made, all the way from templates and cut off wheel to actual torch to a CNC driven cutting bed.

Best of success!

Hey group!

I ended up going with the cast iron cook top.  Just wanted to say thanks for the help and suggestions.  This is such a fun site to keep an eye on.  Lot of different rabbit holes to go down.  In terms of functionality, the stove doesn't get nearly as hot as I had originally hoped (standard temp would be in the 100C to 120C range). Turns out, it works great as a slow cooker (I love ribs). The cooktop works well.

Check the photos below for the end product.

I'm wondering about using the heat for a hot tub.  The cooktop area has a depth of 2.5 inches and 3'x2' LW.  Is setting up a thermosiphon an option? As long as the tub sits higher than the stove, water inlets are below water levels with cold at bottom, hot at top, it should work, right? Can I use flexible copper to snake it in the cooktop area? I have a similar setup for my shower hot water on the roof, using an old fridge for the water tank.  It works fantastically well.  Any skeptics with some words of wisdom?

Thanks again for the awesome information all around!