yet another Wood-burning stove

I hate these things.  I cannot stop making them.  I hate the soot that collects on the two saucepans I sacrificed to wood stoves.  And most likely, the controlling authority where you'll be camping won't let you use these.

Concept:  The gasifying wood burning stove to my knowledge has two parts.  The firebox has air holes at the top and the bottom.  The heat shield is a box that surrounds that fire box.  The heat shield has vents at the bottom to let air into the fire box (primary air source) and up into the space between the fire box and the shield (secondary air source).  The picture below from Wikipedia shows how wood gas from partial combustion flows down from the fire and back up between the fire box and the heat shield with secondary air as both warm up and rise between the fire box and the heat shield, moving back into the fire box when it reaches the top.  "most of the carbon monoxide produced by gasification is oxidized to carbon dioxide in the secondary combustion cycle."  That's the theory.



Instructions on how to build wood gas stoves (some very elegant) abound on the internet.  The variant I developed and show here allows modifications after construction, such as adding more air supply holes.  Of course, it is so cheap to build that one can simply build more.  It consists of two cans which one can find easily in US supermarkets.

Stove construction
Materials:

• Steel tomato can (4" diameter) for heat shield: 104 gm
• Aluminum roof flashing 4.5" x 13.75" to replace tomato can side panels
• Pineapple can for  burn chamber (3.5" diameter) with top off:  75 gm
• 2.5" x 12" hardware cloth for pot support
• 3.5" square of hardware cloth for raised floor

Tools:

• Can opener
• Rotary tool (Dremel or Black'n'Decker RTX for budget minded folk) with cut off wheels for cutting cans
• Heavy duty scissors
• drill and bits
• rivet tool and rivets
• ruler
• gloves, ear plugs and protective eye wear when using tools

Process 

1. Heat shield:  remove top of the tomato can and cook/eat contents.  weight= 91 gm
2. remove label  wt=88 gm
3. Turn the can so the bottom is now the top.  Cut out a 2"circle from the top.  wt=82 gm
4. remove 4 panels from side of can leaving 4 struts (non load-bearing)   wt= 45 gm   (If I do this again, I'll remove two panels & delete step 6)
5. Place Aluminum roof flashing inside the shield and mark four spots at 3, 6, 9 and 12 o'clock.  Cut out air holes at these four spots with the rotary tool.  Attach flashing to inside of can with a rivet at the bottom of the can.  This will bear the weight of the pot support and the pot with at least a liter of water.  Shield wt= 74 gm
6. remove two struts Shield wt= 67 gm  
7. Make fifteen to twenty 1/2" radial cuts from the 2" circle, forming 15-20 tabs

   

   Heat shield with radial cuts on the top.

8. Bend down every second or third "tab" & remove the other tabs.  Heat shield wt= 67 gm
9. Cut away the last two struts and the bottom ring of the original tomato can dropping another 11 gm.  final weight 56 gm.

   

   Heat shield with tabs bent down and side panels removed

10. Burn chamber (burn box):  remove label from pineapple can wt= 71 gm
11. Leave the bottom of the can intact.  It will serve as a heat shield to help protect the surface on which you use the stove.  Flammables will still 
12. Make marks at 3, 6, 9 and 12 o'clock near the bottom of the can.  Draw a horizontal line about 3/4" long at each mark 1/2" above the bottom. The raised floor will rest at this line.  With the Dremel cut four "U"s at the bottom to create tabs to hold the raised floor 1/2" above bottom, bend tabs up.  Now cut upside down "U"s at the same marks to create tabs that you can bend down.  These should be about 3/4" high and narrower than the tabs that we bent up.   
13. cut hardware cloth to go inside can as raised floor 
14. place floor in can on the tabs we bent up in step 11 and bend tabs down to hold the floor.  Burn box wt= 74 gm
15. Pot support:  shape Hardware cloth to fit on top during use and inside the tomato can for transport.  Don't try to cut this pot support so that it's smooth where your saucepan will rest on it, because soot will make the more likely to stick to the pan.
16. I think you're done.  Pot support wt= 15 gm

Total weight 145 gm (5.1 oz), a bit heavy compared to a stove with just the burn box and a simple heavy duty foil heat shield. I suggest you make the burn box with the tomato can and get heavy duty foil for the heat shield.  Just keep it simple.

Storage:  the pot support goes inside the Heat shield and the burn box goes inside that.  It's a bloody tight fit.

Use guidelines:

Place the burn chamber right side up.  remove the pot support from inside the heat shield.  Place the heat shield over the burn box, such that it is centered--the tabs in step 7 may just reach inside the burn box to help with that.  The Heat shield is taller than the burn box.  The gap between the tops of the two cans allows the warmed air between the two cans to move into the space over the burn box and mix with the rest of the burned gases over the fire, supposedly to help burn the wood gases more completely.

The same disclaimers as everybody else has applies. Here it is below:

Disclaimer & Warning:
 
WARNING!!!
Information on this site is provided for educational purposes only.

Neither the webmaster nor anyone else whose information may be included on, or linked to, this web site can attest to or endorse the safety of using any techniques, equipment, supplies or services evaluated or referred to therein. Any endorsement or recommendation is limited solely to the evaluator's opinion about their effectiveness when used for their intended purpose in accordance with safe operating procedures, and if available, in accordance with any instructions provided by the inventor or manufacturer. Some survival and outdoors equipment and supplies are inherently unsafe and can injure, maim or kill even when used appropriately.

Endorsement or recommendation of any equipment, supplies, services or techniques does not constitute a guaranty or warranty the equipment, supplies, services or techniques will function when needed.

Individuals not trained and experienced in use of tools and techniques mentioned on this page should not attempt creating a stove without supervision by someone with proper experience and training.

Wear eye protection whenever flying metal is possible (such as whenever a drill, other power tools, a hammer or knife is used).

Do not light stoves in a area prone to fire, explosion, etc.  Do not light stoves without plentiful ventilation.

Use of gasoline, or any other petroleum products in these stoves may result in severe burns and/or death.