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Home made charcoal retort

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As requested by a friend I have assembled some pictures and steps I took in making a charcoal retort. This way I am not dependent upon finding coal or buying charcoal. I haven't had to buy charcoal for the forge or the BBQ grill since I made this .

Items I used for the retort: 

1 ea  55 gallon drum

1 ea  30 gallon drum

2 ea pieces of black stove pipe. 

10 self tapping metal screws


Pressure wash or scrub the insides of both drums especially if you want charcoal for the bbq grill. 


The first thing I did was to cut around the 55 gal drum @ 2 inches down from the rim on the end with the bung holes to make a lid. Then I cut slits vertically all around the new lid making tabs to slightly bend outwards so the new lid will fit down over the main drum. I then cut a round hole slightly smaller than my stack in the top of the lid to accommodate the stove pipe. Punch or drill holes all the way around the bottom of the drum (the end you haven't cut off) approx every 3 inches. I punched holes that are @5/8ths of an inch.

A mistake that I made was, I forgot to punch holes around the top side just below the lid so my first burn didn't work too well. I punched 5/8ths in holes about every 4 inches. 


On the stove pipe, I cut slits around one end of a pipe and bent the tabs outward to 90 degrees. The tabs on the stack should be screwed to the lid so that the stack covers the hole.


On the 30 gal drum, I cut out the end with the bung holes. Not around the outside of the drum but inside the end so that you have the support of the rim. Like you would a can of beans.


That is all there is to making a retort. Now for the fun part. Making your own charcoal is fairly labor intensive but in my opinion well worth the benefit. Here's some pictures:


 post-14490-0-24637500-1375394975_thumb.jThis is all the parts. Note that I forgot to punch the holes around the top.

 post-14490-0-85369000-1375395030_thumb.jThe 30 gallon drum inverted inside the 55 gallon drum. I'll tell you how in a minute.

 post-14490-0-16561600-1375395060_thumb.jAll assembled and sitting on 4 cinder blocks.

 post-14490-0-68785000-1375395088_thumb.jFlame shooting out of the stack  :)

 post-14490-0-70068000-1375395125_thumb.jThe gas burning from the 30 gal drum. I'll explain in a bit.

 post-14490-0-50349100-1375395170_thumb.jThe next day. And I strongly advise waiting till the next day to peek inside. If you get anxious and open it prematurely and there is just a hint of a spark in the drum that holds your new charcoal, it will begin to burn. NEVER store inside until you are 110% sure it is cold. Hence waiting for the next day to open.

 post-14490-0-71866900-1375395212_thumb.jThe finished product. 


Now for the work to begin.

Take your 30 gal drum and place it open end up on a block or small stump. Fill the inside with whatever wood you want to turn into charcoal. Scrap lumber from a construction site works really well. Just make sure that the wood is dry or you will not get a good burn. All your energy from the original fire will go into burning off the moisture in the wood. 

Don't pack it too tight. You will want some air space between the wood.

DO NOT use treated lumber. I really like oak pallets for the forge charcoal and natural woods like apple, hickory etc for the grill.

Once the 30 gal drum is loaded, take the 55 gal drum and place it upside down over the 30 gal drum. I run two rods through the top holes of the 55 gal drum which are now on the bottom to hold the 30 gal drum inside because you are going to flip the whole thing upside down. Clear as charcoal mud? If not you will learn because all the wood you loaded will spill out if the 30 gal drum is not secure within the 55 gal drum when you flip it.

Place the whole thing on top of some cinder blocks. 

Remove the two rods. Make sure that there is equal space between the two drum walls. You will need to load this area with all the small scrap wood that you can. Fill it up. Then pile more scrap on top of the 30 gal drum which is inverted in the 55 gal drum. Pine cones and pine straw and sticks. Make a good pile. 

It went against my fire behavior beliefs but this will burn from the top down. 

Light the pine cones and scrap on the top of the drum. Once it starts burning, place the lid with the stack on top. The lid will settle down as the scrap on the top burns. 

Here is what will happen:

 As the scrap fire burns down between the two barrels, it will heat the wood in the 30 gal drum. This is where the holes you punch in the 55 come into play. they will create a draft and air source for the fire. 

 Since the 30 gal drum is inverted and the open end is flush with the bottom of the 55 drum, no air will enter in. 

As the wood in the 30 drum heats from the fire between, the moisture will escape out of the open end against the 55 drum. You will see the white smoke escape the stack and along the top. The longer the scrap burns the hotter the wood in the drum gets, It will reach a point where gas will escape from the wood. Once the scrap burns down just about to the bottom, the gas escaping from the wood in the 30 gal drum will ignite. You can see this in the night picture of the retort with the fire at the bottom. The only thing burning at this point is the escaping gas in between the drums. As the gas burns , it cooks the wood inside which produces more gas which  yada yada yada. 

When it runs out of gas the fire will go out. Just let it cool down and come back tomorrow and open it up.


I have had burns where 100% of the wood chars and others where 75% chars. It all depends on the wood and how much moisture is in it. 


Usually you will get about a 30% loss of volume. Remember, you've burnt off all the gas. 


I probably forgot something. Actually the chances are probably pretty good that I did. Please ask questions. I will try and answer the best I can. 

This works really well for me but I know others more experienced will have advice. Please feel free to give your input. 


I am no expert. My father used to say that the definition of an expert was, "An X is an unknown and a Spurt is a drip under pressure."


Mark <><

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Thanks Mark. That is an elegantly simple and very functional retort. I'm thinking it's something that could be adapted into a shop wood heater and retort for a practical multi-tasker. Lots of us either heat or supplement heat with a wood burner. Your retort design or a version I should say, directs most of the combustion and pyrolization heat agains the wood chamber and the outside skin. the outside skin will heat a large volume of shop space while pyrolizing wood for the forge. However if heating the shop is it's job that day a little mod to allow the carbon to continue to burn and direct it's exhaust into the space against the outside skin and it's a high efficiency heater.


Stoking while it's burning is the only real modification challenge and not a big one. Atall Atall.


Excellent design Mark, a fine stand alone charcoal retort as it is on one hand and a potentially high efficieny wood gas heater/furnace on the other. I'm a huge fan of multi tasking tools and equipment. Wood gas furnaces are the rage right now efficient and low emission, win win. So a guy has to have a more permanent set of inner and outer shells rolled. A couple hundred bucks and some welder time noooo big deal at all.


Frosty The Lucky.

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Mark is having trouble posting, so I am forwarding this...


Thanks all!


Thor, The scrap burn is usually about an hour and a half and the gas burn lasts 45 min to an hour. It all depends on what wood you have in the inner drum. I haven't figured out any particulars yet. Usually I light it off and then go into the smithy and get some forging done. 

From in the smithy and from about 50 ft away you can hear the gas burning. It's neat sounding. 


Something I forgot to mention!!!!


Pay attention Frosty!


There is usually a small amount of pitch that comes out of the bottom holes and runs down the cinder blocks. This would make a mess in your shop unless you had a way to catch it. I have seen videos of the large retorts where they put a valve in the bottom to drain and catch the pitch. Then they use the pitch for pitchy things.  My retort is too small and it's outside so I just let it drain onto the blocks.


Mark <><

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frosty, if you want one that is "clean"use one like mine. Burns cleaner hotter and longer! But alas no kiss there and a lot more work to make, better though if you want " black powder" grade charcoal.


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I made a retort style charcoal maker this weekend that's very similar, but there's a few different features on mine.  It worked worked really good for the two batches of charcoal I made this weekend.


I didn't want to step on this thread by posting all the info from my build, since this is a pinned thread, but if anyone wants any further info I don't mind starting my own thread to keep the info and experiences flowing.

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Well like I said, mine is along the same lines.  Right now I'm using a 20 gallon drum for my retort while I'm searching for a 30 gallon version.  If I can't find one soon I plan to just make my own.


I cut the bottom out of my 55 gallon outer drum, leaving a small lip around the bottom to act as a stiffener.  This way I fill the inner barrel with the wood for charcoal, wedging a few sticks under the lip I left to retain the wood.  I then flip it over on top of the bottom I cut from the 55 gallon outer drum.  Once the process is complete and everything has cooled down, I brush away the ash and grab the flat bottom piece with one hand and the inner drum with the other and flip them upright together, this keeps the charcoal inside from spilling out.















































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My very first post, but I've been making charcoal for a few months now, both for BBQ and for an old farrier's forge my brother's currently storing for me.  I've seen the 30gal inside the 55gal drum trick, but decided to up-size it.  I had a bunch of corrugated steel lying around from the walls and ceiling of two shipping containers I cut into pieces when I built my shop.  I built a steel box around the 55 gallon drum, yielding almost twice the volume per batch.  Instead of inverting the drum, I put the lid on and clamp it (you need to hold the lid on, as I found out during the first batch).  I tapped the 3/4" bung for the retort gas and, using some 3/4" EMT conduit, led it down and around the base of the drum.  I drilled a bunch of 1/4" holes in the retort cane, so the whole thing works like a really big burner.


The box is about 30" x 30" x 40" tall and attached at the corners with angle iron from an old bedframe.  The roof is made out of the same shipping container material and just rests on top of the sides of the box.  The chimney is cut into the roof and is a 5ft section of 7" galv duct pipe I had lying around.


After loading the maple (I have a big pile of it from homesite clearing) into the drum and lidding it, I attach the retort cane with a union fitting, bolt on the fourth side of the box, and pack the area between the drum and the box to about the height of the drum top (I've discovered that any more fuel than that is unnecessary, even with punky wood or plywood scraps). Then I put on the roof and the chimney and then light just a single bottom corner.  This seems to reduce the smokiness factor.  Then I just walk away and let it do it's thing.  Or I would, except that it gets scary-hot, so I find myself with a garden hose in hand, spraying down the grass around it and watching for sparks.  Yeah, you'll want to not do this unless you can keep an eye on it for first 1.5 or 2 hours.  After that, things mellow down, the wood from the starter fire is done sending embers, and it's mainly just combustion of the retort gas keeping things going.  It's amazing how much of the gas is produced. 


I'll try to post some pictures of my setup tonight, including the results of the batch I made last night.

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A minor note for the post above:  I really pack the wood into the enclosed drum --  not loosely as shown in the 4th photo of 01Tundra's post.  I tip the drum at an angle and load the logs in so that when the drum is tipped back up, the logs stand vertically.  Anything less than about 4-5 inches in diameter is left unsplit.  Because the maple I have is really dry, the bark is loose and so I choose to pull it off.  This is not really necessary, but it reduces the amount of really fine stuff in the finished charcoal, which is good for the BBQ.


I've forged with coal/coke when my dad had the forge in Colorado (I was in high school at the time), but I have yet to forge with charcoal.  Any opinions or thoughts as to chunk size for charcoal?  Maybe the fine stuff is what I want? 


  - Cheers, 

    Chad McMullen

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I was told to pack the inner drum loosely to allow the escaping gases to flow easily from the inner chamber, but for the next batch I'm going to try to pack it a little tighter.  I've also stepped up the size of the material a little to about 1-1/2" - 2" diameter wood for charcoal.  I prefer larger charcoal for my smoker and it's easy to break into smaller pieces for the forge.  


I know when using coal I prefer smaller pieces in my forge, maybe 1/4" - 3/4" size, not sure on charcoal though.

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This is great. I'm so glad to see others sharing their ideas, their retorts and their experiences. This is what this site is about.


I have packed the wood in the inner drum loose and tight. Loose seems to give me a more thorough burn but that just might be my retort. We will all have different results and so long as we share them we will all improve.


Hey Tundra, thanks for posting your retort with pictures. I may look for a smaller (20gal) drum for mine. Partly because I may want to make smaller batches at times and I think that if I had more space between the drums I would get a hotter and better burn. The 30 gal inside the 55 gal doesn't leave a lot of room for scrap. Enough room but sometimes it's just barely enough. A smaller inner drum like yours may work even better. 


My next retort will be one like Chads where the gas is piped to a burner that runs underneath and the whole setup is in an either steel or cinderblock box.


Keep the ideas coming.


Mark <><

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I did have one burn where the bottom of some of the interior logs didn't completely convert to charcoal.  I've since elevated the drum a little bit to allow the heat to get under the drum.  My theory is that allowing the drum to sit directly on the ground prevented heat from penetrating into the lowest, most interior part of the drum -- the earth acted as a heat sink.  I also put a small amount of charcoal under the drum now (the fines discussed above work well for this) to make sure it gets nice and toasty here too.

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Ian, 01tundra,  Please post them.    we need all smiths to post ideas. it makes us all better.

Already posted under"solid fuel forges/very successful retort" sorry I don't know how to post the link, can you help- Steve?- Thanks!



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  • 1 month later...

I tried doing this method yesterday using a 55 and a 16 as the retort. 




The result was mostly uncharred wood and hardly any charcoal, even after burning for probably 2 hrs, I'm assuming without the lid and stovepipe to heat & draw properly, the gases in the wood inside the retort never ignited.  Maybe it works for smaller materials, but for a decent amount of charcoal for forging I'm putting it down as a failure.  I will get another 55 gallon drum to follow the steps outlined here instead.  Initially the plan was to make it as described in this thread, but found the lid that I had wouldn't fit so decided to give this a try. 

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  • 3 weeks later...

This is probably a ridiculous question, but shouldn't there be some type of "gas escape" for the smaller drum or would that cause the charred wood to ignite?  I'm thinking of making a retort and want to get all the specifics down pat so I don't waste time, money, and wood.

wpearson said it right. For a more visual idea, take a kitchen glass and turn it upside down on the counter. The open end of the glass where it touches the counter is the same as the inverted 30 gal drum inside the retort. As the gas builds up inside the inside drum it becomes pressurized and escapes around the rim and burns. Because it is pressurized, no flame draws back into the inner drum.


All questions are good questions but not all answers are good answers. Hope the visualization with the glass helped.

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  • 2 weeks later...

Mark, i have been seeing burns continuing for around 6+ hours with the first setup I have done.  Do I need to increase the air holes or at least the size of the air holes to try and get it to burn quicker?  And with the weather changing the smoke doesn't seem to want to go away.

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