Charcoal gasifier (simple fire) using 100lb propane tank

Hey guys I’m new here. First post. Iv been visiting this site for 2 years now and basically built 3 or 4 gasifiers in my mind at this point but nothing physical yet. I was in the arm chair phase. My priority for awhile was a long term wood gasifier but then my priorities slowly shifted to more pressing concerns (and they truly were in my defense lol). Well now I’m back on the gasification kick lol. I must admit though, current events is what finally got my butt out of the chair on this one guys lol.

I’m currently looking to build a large charcoal gasifier instead of my dream wood gasifier though. My reasons are that I believe (correct me if I’m wrong) that they are more simple and much more expedient to build over a wood gasifier. From what I can tell also is that they are cheaper to build and safer for the engine due to the absence of tar. All that being said, I knew I didnt wanna do this alone and I also knew thus would be the place to go.

My goal is to CLEANLY run a Generac 7,500 watt generator in emergencies.

The reactor will be a 100lb propane tank (possibly 2 high for a longer run time).

On the very bottom I will have a 5" black pipe and screw cap for emptying out the ash.

The inlet will be a 1" black pipe (as described in the Simple Fire instructions… coupling welded to flat piece of steel, bolted on and cemented)

The outlet will be a 2" piece of black pipe (as soon as the temperature allows, I’ll begin using plastic hose). I may or may not add pressure and temperature gauges there also.

The lid will be like Ben Peterson’s design only simplified a bit for my skillset. Spring tightly pushing down. The seal I’m not sure of just yet… maybe wet fire rope?

The filter I’m still designing but will probably be another propane tank filled with hay/foam/and wool blanket.

I’ll attach a picture I drew of the reactor.

What do you guys think? Any faults in this plan? Things I overlooked? What would you guess the run time to be using a 7,500 watt generator?

Thanks guys!


Hello David,
I built a very simple charcoal gasifier out of the center pipe from a water heater, 4.75 inch diameter. I use 1/2-3/4 inch charcoal.
I do not use a cycle filter. Though I made one. It seems that the unburned charcoal above the hot zone acts as a filter. I use a simple filter that I made out of a plastic bucket. The filtering element is just four socks slid over a pipe with a lot of holes drilled in it.
I live in Colorado, so finding very dry wood is easy. It is important to have dry wood. I started making charcoal in a simple tlud (top lit updraft) that I had made out of coffee cans. I later made a 50 gallon tlud out of the same old water heater.
I like having fill and dump hatches on the top and bottom. Filling and clean out are easy.


David, Welcome to DOW.

Just a thought—as I looked at your drawing and read the description—do make the air inlet part which contacts the charcoal (the nozzle) so it can be removed at least from the inside. It would be even better if it was removable from the outside. This is so it can be renewed and possibly replaced with different designs until you are satisfied with the results.


Hello David!

You chose your path wisely. A simple charcoal gasifier is the way to go to get feet wet.

My humble opinion. Top to bottom. The lid will work and can be sealed even with rubber. Not much heat there if all is ok and enaugh fuel of the right size. But, for charcoal, there realy isnt a need for spring loading it. I have never had or heared from anyone having a puff in a charcoal hopper. Allso, the lid can be much smaller. Unlike wood chips and chunks, engine grade flows like corn kernels. 4" is about the limit, everything biger will not jam.

If you do decide to extend the hopper, thats a good idea. But, you can then have the gas exit midway, less drag on the gas.

Then the most important part. I strongly recomend you rethink your nozzle design. A simple fire style horizontal nozzle is great for what its ment for; throwing together a bucket and 2 pipes and making a gasifier in minutes. But for any extended amount of run time invest some more work in it.

I am a big fan of vertical nozzles. If you just drill the cleanout cap and place the same nozzle trugh it verticaly l am comfident your nozzle will last 3 times of what you showed. If you invest some more work to it and maybee install a flute nozzle and even a drilled reversed cap like someone here did a few daysago (my deep apologises to the person. I skiped trugh the tread without paying atention to who made it. All l know is l am impressed :wink: Please chim in). Theat nozzle will last preety much forever.


Regarding the lid, I suggest using the domed end of the propane tank and cutting a hole in it leaving about a 2 inch lip all around. Then use another domed top as the lid. They will nest.together nicely. Apply spring tension in 5he center. A ring of high temp silicone will seal it.
I think it was Jim Laplante who first suggested this to me. I used it on my simplefire and it worked good.


Reducing bushing. Say 1 1/4 to 1" welded into the tank and then 1 inch to 3/4 or half inch. whatever your nozzle is going to be. The bushing threads do not run all the way through but you can grind a slight taper on your nozzle pipe and drive it into the removable bushing. Pack a little furnace cement around the space the nozzle doesn’t quite fill. It will hold. I’m pretty new here myself. These guys will help you anyway they can.

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David and Tom,
You may know this already–one item which I have discovered, but not used yet, which allows removal of the nozzle from the outside is called a double-tapped tank bushing. This screws into the welded or bolted on flange fitting and has a smaller threaded hole which allows plumbing fittings to be screwed in from both sides.


Nope. Did not know that. It’s very good to know. Glad I didn’t already weld the bushing into the unit I’m building. Thanks.

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Sorry for the delay guys. I had a little accident and got myself a hernia (I know I know… your all jealous lol). I’m finally healed up and getting back into my routine now. When I get off work I’ll show you my updated design and see what you all think about it!

Great advice guys. I like the ideas


Good to hear DavidS.
Yep we all over-do at some time hurting ourselves. Mine is a decades back separated pelvic bone girdle 150 pounds carrying in a tight attic storage area and one leg pivoting turning. Stupid. Stupid, me. I was hard torso crunched to protect my spine and and guts. Opps. Something; will-force driven, was going to give.

I am linking this post back to KristijanL’s use-based advices.
You would do good reading back his (just click on the upper R.H. arrow swoosh of his smiling face) direct advices to you.

Ha! Realize GaryG’s Simplifier concept is Doing Less to get More.
Do not fall into a brainac/manic-fabricator trap some do; over-complcating, just 'cause. . . .

Steve unruh


Steve U,
The last couple of days I had been thinking the final thought you express, but didn’t want to hurt feelings. I have noticed at various time in the past, people who have the skills and experience to do complex things will often make simple things complex. OK I have said it. Now I feel better.


Haha, yeah, this made me chuckle a bit, because I find that I do exactly that. Sometimes I only think I have the experience :grinning:

At the end of the day, though, I think it is only a trap if you are not learning something from it. Anyone could build a simple fire; you can even put one together without touching a welder. If you need something to just work and be made out of scrounged stuff, this is the “best” solution. But it will not teach you to be a better welder or fabricator. I have built all sorts of contraptions, and I learn as much from the ones that work terribly as the ones that work okay (someday something I build might even work really well!)

You bit off a big bite for a first attempt, but the nice thing about steel is that you can keep cutting it up and modifying it until it does what you want it to, or you lose interest and build something else. My scrap pile has a lot of weird little doodads that didnt quite make the grade. Maybe I should start welding them into some sort of sculpture.


Hey, I think you guys are talking about me. I have never seen anything I couldn’t make more uselessly complex. I may have been Rube Goldberg in a previous life.


Hey Tom , bless you my friend if you want to make life hard for yourself then go on ahead don’t mind us .


Still i love your work so far i just cant wait to see it run



it looks more complicated than it actually is. My only concern is firstly, that it works and secondly, that it won’t need to be replaced anytime soon.

I’m unsure about the nozzle but I guess I’ll start with a plain old 1" black pipe and experiment from there. Its cheap and easily replaced.

The initial suction will be a shop vac. Any concerns about electrical sparks igniting the gas? I see people using them fine.

The ash cleanout is a 5" black pipe and black pipe cap (iv had that lying around for 2 years. Thing was like $50!)

I dont have the exact plan for the carburetor attachment yet but it easy enough to whip up

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Looks just right to me. And really nice clear sketch too.


thanks Andy. I can be a perfectionist on paper. I draw and write it twice lol. First lightly with pencil then clean it up with a felt pen

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What are your thoughts on this during a grid down situation? Would this run a 7,500 watt generator or only something smaller? I could always cut and add a second 100lb propane tank to add capacity.

Is there a better charcoal gasifier design for my needs that isn’t going to cost me an arm and a leg?

Sorry for all the questions but I need guidance in this endeavor. I’d hate to build something only to learn its not what I need

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I think you are on the right track, what you have sketched up would absolutely work. I am not sure how long it would run a 7500 watt generator, I would guess it would probably run an hour or two though, depending on load? Maybe someone else will chime in with better estimates. The size of the engine is pretty flexible with charcoal, but a bigger engine obviously will burn through the fuel faster, and also make a bigger hotter reaction that will overheat sooner. Bear in mind that you will not get the full rated gasoline output - so if you need 7500 W in output, you will probably need the generator to be rated a bit higher.

The only change I would suggest is the nozzle. The thread on charcoal nozzles is worth a read, and Steve Bowman made a nice example of the flute nozzle using threaded iron pipe.

You probably would not need more than one hole for a small engine. This style of nozzle has a good track record for durability. Looking forward to seeing it up and running!