WK Inspired Wood Stove/Oven Idea

I was just thinking about what to do with some scrap that can’t really be used for either a standard gasifer or other projects I have and I think I may have found an interesting idea to try. I’ll try to get around to drawing up a diagram or 2 when I have more time.

I hope Steve U. can chime in as he knows about these things. I have made some vaguely educated assumptions about woodgas and woodstove theory that I don’t know for sure:

  1. Until heat has either gone up the chimney or leaked out through the walls of a house, no heat is wasted in a wood stove.
  2. Heat produced in a woodstove is used for; drying out the soon-to-be burned wood/fuel, breaking down more fuel chunks/molecules, moving gases via convection, heating the surrounding area (intended goal), or being wasted out the chimney.
  3. “Heat Units” (but not the heat itself) can be wasted in the form of unburned fuel leaving chimney.
  4. Recycling some heat back into the fire, in the form of preheated air (Primary and Secondary), will help burn more fuels, more completely, releasing even more stored heat in the process.

If these are true, wouldn’t a WK-inspired hybrid gasifer/stove be very efficient? Except maybe scale, the fuel hopper and fire tube assembly would probably be unchanged from a larger vehicle-mounted WK gasifer. Since it is a stationary unit and shock and weight aren’t as much of a concern, I’d think adding firebrick liners down at the restriction to help keep that area safe but hot enough to really break things down might be a good idea.

Because there is no engine to suck on the unit and I don’t think a chimney draft is strong enough to pull gas through the system, Primary and Secondary air inlets would need to be pressurized/force-fed, in an adjustable manner. Unfortunately, this breaks from the “let the source suck only what it needs” rule of standard gasifiers.

Air would be blown into a large heat-mass/heat-x to gain some heat from the end product. It would split (with an asymetrical T-joint) with most of the air going on to become Primary air and some getting put aside as Secondary air. Primary air would enter into a standard WK firetube assembly taking excess heat off of the firetube, as normal, mixing with wood from the hopper above and burning. Hot smoke and gasses flow down through the charbed getting broken down.

The gas exits the gasifier and goes back to the heat-mass/heat-x where it mixes with the Secondary air that we’d preheated and shunted off before. I was visualizing a very heavy cast iron pipe/tube, maybe 4-6" in diameter, optimally with fins molded onto the outside. This tube will be called the “Burn Tube”, since “Fire Tube” is already taken. The gas enters into the inner area of one end of the pipe while a second, much smaller set of nozzles blows the Secondary air around the gas into the same end of the pipe. Since the gas is still hot, it ignites and burns as it goes down the Burn Tube.

MORE LATER! Out of time!

http://www.hearth.com/cgi-bin/top13.pl?banner=boiler3;time=1374064384;zone=boilertop. Hi brian, maybe some of these type of boilers would provide so design ideas. There are other designs of boilers on the site that operate on same principal with forced draft, induced, or natural draft.

Gee Brian are you sure you want me to comment on this??

Very nice link to the best in class Garn system AllenR.
This is the one I recommend to people wanting to woodfuel heat but un-willing to have an in-room, in-house modern efficient woodstove. Yep Garn for the 90%+ conversion efficiency AND actually needing to be inside intalled in a finished/semi-finished space. I cannot concieve of any sence of having to outside hat, coat, boots up to go out in the dark, the cold, the rain/blowing snow to stoke an OWB “Smoke Dragon” even twice a day!
Easychair house slippers on trundle out to the attached garage or down to the basement and chuck in some more FOUR FOOT/ONE METER LONG LOGS into the Garn firebox once/twice in a 24 hour period. That makes practical sence to me.

BrianH a good deal of the efficiency in a bulk burning wood heating stove is only having to in comparision to a gasifier minimally pre-process the fuel wood.
The Garn is built to take actual full cord length wood logs. Thats fuel prep effiency.
Any built right, and operated right woodstove you can actually fuel with the tree “dark meat” “crap” portions that would choke any gasifer down into a tar monster.
My woodstoves are where now I use up all of my punk/rotted woods, pitch woods, barks slabs&chunks, limbs down to 1/2 inch (13mm) and big hard irregular knot pieces. Put those, been in the past burn pile wasted BTU’s right now into my house heating equation. That’s sweat and full tree “squeal” usage efficiency. Normal wasted portions now visible smoke free 95% of the time converted into needed in the house heating.
With a good established hot in the stove coal bed even paper sacks of woodlot/splitter stranded, stringy waste “chips”.

Often for true full cycle efficiency it is steps what you can cut out of the cycle to not have to then; Do, Build, Maintain and wearout Replace. Far too easy can make things compex and idealized. Takes real genius to make it the best functionally and simple.

Steve Unruh


If you’re really trying to maximize the extracted heat from a wood appliance, have a look at the rocket mass heaters. They claim extremely high efficiency due to the large mass and super insulated chimney. They can exhaust very low temperature “smoke” really mostly steam. That plus some quality insulation…in a small well insulated shop or cabin I think you’d be quite snug. But this stove requires “high grade” wood fuels; smooth straight sticks that can fall down together; big gnarly pieces are impossible. The reward here is clean efficient combustion and less time firing the unit.


www.mha-net.org for the real scoops with lots of pictures
also google Masonary Heater Stoves
You will even find prefabricated free standing mass heater stoves available now.
You will see most have glass fronted doors to get that bone warming char glow out into the room.

Masonary mass heater efficiencies of 90-95% true wood energy potential to heat into the house are very real and universties and even DOE cited measurements of this. Finns and Russians been doing this for hunderds of years with natural draft chimneys. To do this with occupant safely the keys are:

  1. to always have an airtight door system to be able to shut off complelty all gasses flow once the thermal mass heating up by the very rapid draft induced forced air burn cycle is done. DO NOT REFUEL. Air shut down. Reheat later in time separated batch cycles.
  2. have enough thermal mass to store the rapid over aired single fuled burn cycle released heat in. This has been shown to be as little as 350 pounds in cast refactory componet hearths. That system pictured in a http://thriftyandgreen.com article.
  3. have long enough of a labyrinth combustion gasses pathways system to slow way down the gasses flow rate and allow the hot gasses to heat transfer into the thermal mass.
  4. use a “Norwegian” top lit burn downward combustion burn cycle to oxidize to heat all of the fuel wood heat released outgases.

A very smart offgrid friend of mine researched out and built one for his family. He’s of direct Swiss decent and visiting felt the heat and seen the wood fuel used economy been used there for hunderds of years doing this in thier masonary “tile stoves”.
SS insulated all metal through the roof chimney pictures in thier “Stonehill House” photo album.

And ain’t none of these in-use systems that will allow use of a thin, thin 19 guage steel layer between the CO gasses and the sleeping occupants.
Friend MarcusB is an actual working MD and would not have a killer rocket stove in-house with his loved wife and thier two loved childern. Got any real good EMT/fireman friends? Keep a friend and do not show him your rocket stove creation.

I feel a little bit like Charlton Hestons character being dragged off to be silenced still insisting “Soylent Green is people!!” on this rocket stoves danger in occupied spaces issue.
It’s like saying openly that 200 MPG carburators have not ever, and could not ever exist. Poor Pough was sensationalized newspaper dragged into this without his consent - he only ever claimed a 25% improvement. The Fish carburetor wasRreal and can still be bought www.mikebrownsolutions.com/Fish-carberator - it’s sonic- very noisy and will double you previous carbureted installed milage but with some loss of power and trasition responce. Port fuel inject it as done now and do the same. Featherfoot/hypermiles techniques drive and do the same for no payout costs at all. The GEET system is an over-promoted, under-rpreformer again beat with modern port fuel injection on any comparable application.
Openly dispute any of these is just like saying there are NO Free Lunches in life truely - just conned, stolen ones.
Lunch thieves do not like you pointing that out to thier Marks at all. You just might upset thier conned dribble in cash flows.
Well at least ALL of the professional engineering organizations, fire safety organizations, insurance companies and every single state and northern hemisphere country with woodheating histories are saying the same thing - rocket stoves are dangerous as having NO air tight shut down doors; a dependency on absolutely 100% gases tight metals constuction for as long as it is ever in use - yeah, right - with common barrels?? ; and not having failsafe (every go cold cycle) always updraft gasses flow paths.

Your article writer and info seller ChrisKY is playing it very fast and loose with his efficiency numbers. And I read now two more dedicated rocket stove “over 700 systems built” overpromoters very obvious never operated a 1996 and later clean burn certified woodstove with a good chimney. Another two that are gonna “come and get me”. Phsss. Comparing to old style non-improved woodstoves and fireplace efficiencies. Just about anything can improve on those. Just like like your hypermilaging I can 2X improve those with just operator techniques. I spent many more years back in the past with those than now in the present with modern capable.
This would be is just like comparing the improvements of a bolt on TB conversion system put on your old style 318 to “before with a carbutetor”. HooRah! Great!
You know well that would still not give it the 318 MAGNUM performance and full range warm up and trasition smoothness you now have.
No Sir - No Sale. I saw the strings - again. No lead into Fools Gold for me.
I will happily keep my “only” 85% verifieable true efficient fuel wood energy to delivered into the house woodstove because with 3 dogs, 3 cats ( at least a three child track in equivalency) and an aways very wet ME in and out for 9 months out od 12 we need the extra air changes to be woodstoved pumped to get all of that vaporized wet out of the house and ytry and dehumidify. Woodstoving is great for that. Woodheat dehumidified and air changes here in the rainforest makes the house smell great. Electic heated it gets people/critter/mold stinky and clammy sweaty within just two winter wet days.

ANOTHER overlooked woodstoving efficiency BrianH. over running the electric driven whole house air changing system and just blowing expensive heated air out to get some fresh air in. Whole house sickness is very real for you and I here in the GreatWet.

Steve Unruh

Thanks for the info Steve, I wasn’t familiar with the low-down on rocket mass heaters. I am a bit disappointed, the marketing geniuses have really smoothed it over and made it look attractive.

Woodburners are not very selective in fuel size and shape. So why take the effort of building a relative complex gasifier and make well sized wood, when a simple to build and female friendly woodburner also does the job.

I have all my woodburners and cooking stove equipped with rocket stove technology. Often the addition of an internal “letterbox heat riser” makes a huge difference. It acts as a pump, thus helping chimney draft, which makes downward directed flows around ovens easier.

Do not use the conventional open feed tube for inside use. In home you want a closed fire chamber. An acquaintance put rocket combustion technology to a higher level by developing the letterbox heat riser. See this thread: http://donkey32.proboards.com/thread/511

Here some pics of our summer cooking stove. It’s an RMH and eats everything between small saplings and 7 feet long logs.