A biochar kiln is any container that is used to make biochar. A key feature that separates a biochar kiln from a conventional fire pit or burn pile is that a biochar kiln keeps air away from wood while it is hot enough to char. There are four common designs. We have listed every biochar kiln for sale in the US that we could find with its price (as of the day this article was written) listed below. We also listed some DIY biochar kiln plans for building your own. This guide compares the designs by how they work, what they cost, and how much wood they can handle at one time.
The four kiln types
Every kiln works on a similar principle: when wood burns, it first releases gases, which burn and make the big flames. When the flames die down and you are left with hot coals that do not make much flame, you are left with mostly just carbon in the char. Stop burning the hot coals and you are left with charcoal. Charcoal used as a soil amendment is called biochar. The designs differ in how they reduce the amount of air reaching the hot coals.
| Type | How it works | Tending | What you get | Best for | Watch for |
|---|---|---|---|---|---|
| Flame-cap kiln (Kon-Tiki family, our fire pit, most backyard kilns) | An open steel cone, pyramid or ring with a closed bottom. You add a layer of wood each time the flames die down. The flames across the top use up the oxygen coming in from above, so the char underneath does not burn to ash. Water is used to quench the fire and stop the burning.[1] | Someone next to the kiln the whole time, 2 to 3 hours for wood. | Coarse, clean char the same afternoon. Typically less smoke than a pile or a conventional fire pit (air in from the bottom) when run right with dry wood. | Prunings, trimmings, firewood scraps. The size of the kiln sets the size of the job. | You need water on hand. |
| Pyramid, trough and ring flame caps (Oregon Kiln, Ring of Fire, farm Kon-Tikis) | Flame-cap. Panels bolt together in the field.[2] | Big flame-cap kilns should be used with two people. | Cubic yards of char per batch. | Brush piles, orchard prunings, forest thinning. | Weight, price, and a lot of water to quench. Not a backyard fire pit. |
| Biochar retort (sealed drum inside a fire) | Wood is sealed in a drum. A separate fire around the outside heats it. The gases vent out and burn off. The drum stays shut until it is cold. | Less tending once the outer fire is going, but you feed that fire too. | Big, uniform pieces. Good grill lump. | Making charcoal to cook with. Small batches. | Burns extra wood to run the outer fire. Cools overnight before you can open it; open it early and the char lights. Can smoke badly. Not recommended due to excess pollution compared to the other designs. |
| TLUD (top-lit updraft) | A drum of small, uniform fuel lit on top. Air comes in through holes in the bottom, the fire front travels down, and the gases burn in a chimney above. | Little tending once lit, but you cannot add fuel mid-run. | Fine char from chips, pellets or nut shells. | Uniform small fuel. Cook stoves. | Needs sized fuel, and you have to stop it before the char burns. Poor with mixed prunings. |
| Pit or trench | A flame-cap fire in a hole in the ground.[1] | Same as the flame-cap kiln. | Char with dirt in it. | Free, and it takes long pieces if you dig a long trench. | Digging. The heat cooks the soil under it. Not allowed in a lot of places due to city restrictions. A hole full of hot coals at ground level: not anywhere children or pets could be. |
How a flame cap works: Kon-Tiki, Oregon Kiln and Ring of Fire
Most of the kilns you can buy are flame-cap kilns, so it is worth understanding the trick. A pile of wood burning in the open gets air from every side, and the coals at the bottom burn away to ash. In a container with a closed bottom and solid sides, the only air comes in over the top. Once the fire is going, a layer of flame sits across the whole surface and uses that oxygen up before it can reach the coals below. The wood under the flame cap gets hot enough to char but does not have enough oxygen to burn completely to ash, so a bed of glowing char builds up as you add layers. The flame cap also burns up most of the smoke on its way out. You keep feeding it until the kiln is full of char, then fill it with water.[1]
The most popular design is the Kon-Tiki, an open-source cone published by the Ithaka Institute in Switzerland in 2014.[3] The drawings are free, which is why there are so many versions. The three you will see in the US:
- Kon-Tiki. A steel cone about 5 feet across at the top, built for farms. Finger Lakes Biochar builds them in New York. Big enough for a small brush pile in an afternoon.
- Oregon Kiln. A four-sided pyramid in 14-gauge steel, developed by Wilson Biochar for forest thinning work. It is the design Utah State's extension program adopted for fuel reduction, because it makes much less smoke than pile burning and does not cook the ground under it.[2]
- Ring of Fire. Wilson Biochar's newer field kiln: a 7.6 foot ring of panels, 40 inches tall, that two people bolt together where the pile is. It takes 2 to 3 cubic yards of brush per batch.
Our own Biochar-Making Fire Pit is the same idea sized for your backyard: a 24-inch cone that works like a fire pit while it makes char, with a pipe in the bottom so you can quench from below. It is in the table with all the other designs.
Biochar kilns for sale in the US, with prices
Prices below were read from each seller's site on September 10, 2026. They change, so treat this as a snapshot and check before you order. Sorted from small to large. If you are looking for a biochar retort for sale, we did not find one among the US sellers below. The two stainless drums from Biochar Station and Eartheasy are TLUDs (the fuel is lit on top and a chimney goes on), and the rest are flame-cap kilns. All are portable biochar kilns: the small ones ride in a pickup, and the field kilns bolt together where the pile is.
| Kiln | Type | Size and steel | Price | Shipping |
|---|---|---|---|---|
| The Best BioChar Kiln (Washington, non-profit) | Flame-cap, riveted flat-pack kit | 30.5 in across, 11 in high. 20-gauge US steel, two sides and a bottom you rivet together. | $172 | Flat rate by region |
| Eartheasy stainless kiln | TLUD | 3 gallon and 6 gallon drums, stainless. The same two drums as Biochar Station's, sold under Eartheasy's name (the barcodes match). | $351 and $523 | Ships |
| Biochar Station stainless kiln | TLUD | Small and medium, 0.073 in stainless, seam welded, an inner fuel chamber lit on top with a chimney above. Larger cold-rolled and 55-gallon models above that. | $323 and $488; $640 and $2,350 for the big ones | Ships |
| Pi Fabricators Biochar-Making Fire Pit (Salem, Oregon) | Flame-cap, with a quench pipe | 24 in across, 19 in tall, 11 gallons to the rim. 16-gauge steel welded in one piece, 21 lb. Doubles as a backyard fire pit; grill and griddle fit it. | $370 | Free in the continental US, five-year limited warranty |
| Howard EcoWorks (Maryland, non-profit) | Pyramid flame cap | 16 in square bottom, 32 in square top, made by a local artist. | $430 | Pickup only |
| FlameWise | Flame-cap kilns | A campfire size and a burn-pile size. New seller, first kilns delivered in 2025. | From $550 and $750 | Ships |
| Earthly Biochar (UK) | Double-wall flame cap, cooks | Compact and Original. | $649 and $1,299, delivered | Ships from the UK, tracked. Their page says shipping and duties are included in the price. |
| Finger Lakes Biochar Kon-Tiki (New York) | Flame-cap, farm size | The full-size Kon-Tiki. A tilting version with forklift slots is $1,250. | $1,125 | Pickup only, no longer shipping |
| Ring of Fire (Wilson Biochar, Oregon) | Flame-cap ring, field size | 7.6 ft across, 40 in tall, 335 lb, 5.6 cubic yards. 2 to 3 cubic yards of brush per 4 to 5 hour burn. | $1,995 | Free to the nearest freight terminal |
| CharCone 24 (Massachusetts) | Flame-cap, kettle-grill size | 24 in top, 13 in bottom, 12-gauge bowl, 64 lb with the shield. | Not currently listed; reported out of production | Used ones turn up |
Prices checked September 10, 2026. Sellers' own pages, before tax. The Earthly Biochar figures are the US-facing prices; their page says shipping to your door and duties are included.
Wall thickness, warp and weight: what the gauge number means
We build these, so this is the part we get asked about most. Sheet steel is sold by gauge, and a smaller number means thicker steel:
| Gauge | Thickness | Who uses it | What it means |
|---|---|---|---|
| 20 | 0.036 in (0.9 mm) | The Best BioChar Kiln flat-pack kit | On the lighter side. Light and cheap to ship, but more likely to warp or bend when it is hot. |
| 16 | 0.060 in (1.5 mm) | Our 24-inch fire pit | Thick enough that a 24-inch cone holds its shape and still weighs 21 lb, so one person can carry it. |
| 14 | 0.075 in (1.9 mm) | Oregon Kiln panels | Heavier, for larger kilns. |
| 12 | 0.105 in (2.7 mm) | CharCone bowl | Very durable. A 24-inch bowl in this steel weighs about three times ours. |
| 11 | 0.120 in (3.0 mm) | Large kilns; our build-to-order kiln | Very heavy duty, for large kilns. Holds its shape under a big fire and resists thrown firewood. |
Stainless does not rust, but it expands more when it heats up, which makes it more susceptible to warping.
Two things the gauge does not tell you. First, how the pieces join: a continuous weld does not loosen or leak, and rivets and bolted seams can. Second, the finish. Bare mild steel darkens and rusts to a patina and keeps working; that is what our fire pit does, and we tell people to expect 10 to 15 years without doing anything to it.
Which kiln for which pile
Pick a kiln based on how many prunings your backyard makes. A kiln that is too big for your prunings sits in the yard. If you have a few acres, you might want to consider a big kiln.
| What you have | What fits it | Why |
|---|---|---|
| Prunings, hedge trimmings, firewood scraps, a wheelbarrow at a time | A 24 to 30 inch flame-cap kiln: the Best BioChar Kiln flat-pack kit, our fire pit | One batch, 2 to 3 hours, takes a wheelbarrow or two of dry, cut material and makes a few gallons of char. Repeat as the prunings come. |
| A real brush pile, cubic yards of it, once or twice a year | A farm Kon-Tiki, the FlameWise burn-pile size, or the Ring of Fire | You want to finish the pile in a day or two, and these eat cubic yards per batch. Above about 3 cubic yards the answer is a bigger kiln. |
| Acres of thinning or orchard prunings every year | Several field kilns | This is the scale the Oregon Kiln and Ring of Fire were built for. Cost-share programs sometimes cover them.[2] |
| Wood chips, pellets, nut shells, and nothing bigger | A TLUD, or a flame-cap kiln | A TLUD is finicky and wants small, uniform fuel like this; it does not take larger prunings, which is what most backyards have in them. A flame-cap kiln handles small fuel fine and larger pieces too. |
DIY biochar kiln plans and designs
You can make good char without buying anything, and the flame-cap principle is forgiving. Most biochar kiln designs come down to the same three things: a closed bottom, solid sides, and water to finish.
- A solid steel bowl or stock tank. Any steel container with a closed bottom and no air holes is already a flame-cap kiln. Utah State's extension program makes biochar in plain stock tanks.[2] Not a galvanized one: the zinc coating burns off as a fume you do not want to breathe, so use bare steel. A regular fire pit with air holes in the sides or bottom does not work; the air reaches the coals and you get ash.
- A trench. The cheapest kiln there is, if you are allowed to dig and burn where you live. Start a fire in the trench, add a layer each time the flames die down, and flood it when it is full.[1] The soil under it takes the heat. It is a hole full of hot coals at ground level, and a child or a pet could fall in. Do not use one anywhere children or pets could be.
- The Kon-Tiki drawings. The Ithaka Institute published the cone as open source, and Open Source Ecology keeps a set of biochar kiln plans and build notes.[3] A local sheet-metal shop may be able to make one, although many shops will not be able to roll the cone; welding or bending a pentagon or hexagon is something most shops near you can do.
- A 55-gallon drum biochar retort. The classic 55-gallon drum with a smaller sealed drum inside it. It is possible, and people build them, but it burns a lot of wood to heat the outer drum, it smokes a lot, and it has to sit sealed overnight. Because of the pollution we do not recommend it.
If you are using any flame-cap kiln, the process is the same as for our Biochar-Making Fire Pit. The how-to guide walks through step by step.
Before making biochar. Check with your city, county or fire district that open burning is allowed, whether you need a permit, and whether a burn ban is in place. Water ready before you start the fire. Level, fire-resistant ground, nothing overhanging, no wind. Someone tending the fire until you quench it and the char is wet and cool to the touch.
Common questions
What is the difference between a biochar kiln and a conventional fire pit?
Air from below. A conventional fire pit is built to let air in under the coals so the wood burns all the way to ash. A biochar kiln blocks that air, so the coals stay as char. A steel fire pit with a solid bottom and no air holes will produce biochar; one with vents will not.
How much biochar does a kiln make per batch?
It depends on the kiln's size, and when you quench, so we give ranges. Our 24-inch pit makes about 2 to 4 gallons of char per batch when it is tended well. A large Kon-Tiki can make cubic yards. You can get an estimate of how much you produce each batch by adding the biochar to a 5-gallon bucket.
Is a biochar maker the same thing as a biochar kiln?
Yes. Sellers use "biochar maker," "biochar kiln," "char cone" and "biochar retort" when talking about a biochar kiln. The word that matters is which type it is: flame-cap, retort or TLUD. The table at the top sorts that out.
Is a stainless kiln worth the extra money?
For a flame-cap kiln, no. Plain mild steel rusts to a patina on the outside and keeps working for years, and the inside is scoured by every fire anyway. The two stainless kilns in the table are TLUDs, and we have not run one.
Can I make biochar in a smokeless fire pit?
Not in a typical smokeless fire pit. Double-wall pits feed air under the fire on purpose, so they finish wood to ash.
Do I need a permit for a biochar kiln?
Usually the same rules as a recreational fire or open burning where you live, and they vary by city and season. Many cities allow a contained fire of clean dry wood (with size restrictions) and prohibit burning yard debris. Ask your fire district.
Sources
- South Umpqua Rural Community Partnership (2018). On-Farm Biochar Production and Use, Practice Guideline: Using a Flame Cap Kiln to Make Biochar. PDF hosted by Oregon State University Extension. The flame-cap mechanism, trench and cone kilns, layering and quenching.
- McAvoy, D. (2019). Hazardous Fuels Reduction Using Flame Cap Biochar Kilns. Utah Forest Facts 037, Utah State University Extension. The Oregon Kiln in 14-gauge steel, stock-tank kilns, smoke compared with pile burning, kiln consumption of 4 to 8 times its own volume per batch.
- Open Source Ecology wiki, Kon-Tiki Kiln, with the Ithaka Institute's open-source design (Schmidt and Taylor, 2014). Plans, dimensions and build notes.
- Seller pages read September 10, 2026: bestbiocharkiln.com, biocharstation.com, eartheasy.com, earthlybiochar.com, howardecoworks.org, charcone.com, fingerlakesbiochar.com, ringoffire.earth and wilsonbiochar.com, flamewise.com. Sheet gauge thicknesses are the standard US sheet-steel gauge table.