A smokeless wood burning fire pit has two walls. Air comes in at the bottom, heats up between the walls, and comes back out through a ring of holes near the top, where the air provides extra oxygen to fully burn the smoke. That's the trick, and it works. This page explains it, says what the fire pit is built to leave behind, answers the question (can it be used to make biochar?), and compares it with the flame-cap fire pit we build.
Can you make biochar in a smokeless fire pit?
Not by design. A smokeless pit feeds air in under the fire on purpose, and air under the coals is exactly what turns biochar into ash. Run one the normal way and you get a clean burn, and a pan of fine ash when you are done.
There are two workarounds, and both have a catch.
- A pot in the fire pit. Put dry wood chips or small sticks in a steel pot or a paint can with a lid, punch a small hole in the lid for the gas, and set it in the fire. The wood inside chars without air. This is a small retort, and it makes a few cups of biochar per evening. The catch is the size: it is a science project, not a way to feed a garden bed.
- Quench early with water. Let the fire burn down to a bed of glowing coals, then flood it before the coals turn to ash. You will get some biochar. The catch is that most smokeless pits are not built to be flooded. The makers say not to, the double wall traps the water, the ash pan and the vent holes clog, and thin stainless does not like the shock. A kiln is designed for that thermal shock, which is the difference between a conventional fire pit and a biochar kiln purpose-built for the job.
If biochar is what you want, the container has to block air from below and tolerate being filled with water while it is a few hundred degrees. We cover different types of biochar kilns for sale in the biochar kiln buyer's guide.
How the double wall works
Wood smoke is mostly unburned fuel: gases and tiny particles that leave a fire before they can cleanly burn into CO₂ and water. A conventional fire pit with air coming up through the bottom pushes these gases and particles up above the fire without enough mixing for them to fully combust. A smokeless fire pit heats air in the gap between its two walls and pushes it out through the holes near the rim, where it mixes with the hot smoke and gives it the oxygen to burn completely.[1] A flame-cap fire pit does a version of the same thing: air warms as it rises along the outside of the slanted wall, rolls over the rim and mixes with the smoke coming off the flames, so it finishes burning too. The double-wall pits just do it more aggressively. The Solo Stove, the Breeo, and the dozens of other smokeless fire pits work on the same principle, and so does a smokeless fire pit insert or a smokeless fire pit ring that drops a double wall into a fire pit ring.
- Air in at the bottom. A row of holes around the base of the outer wall lets air in. Some of it goes straight under the fire through the floor and feeds the coals. The rest goes up.
- Heated in the gap. The space between the two walls heats up the air, causing it to rise. The double wall allows the air to get hotter than a single wall would, which causes the air to rise faster.
- Out through the holes at the rim. Near the rim of the inner wall is a second ring of holes. The hot air comes out of them at a higher speed, agitating and mixing the smoke rising off the fire so it reburns. You can see this as the row of small flames dancing above the holes once the fire pit is going.[1]
It is not smoke-free. Every maker says so in the fine print, and they are right: the rim jets need a hot pit, so you get smoke while it warms up, smoke when you drop wet or oversized wood on it, and smoke again as it dies down. And the reality is that no smokeless fire pit is smokeless at any time, just a lot cleaner burning than a conventional fire pit.[2] In between, with dry wood, it is very clean. Ours is single wall and we do not call it smokeless either. Run right, with a flame cap across the top, it burns much cleaner than an open pile or a conventional fire pit, and for the same reason the double-wall pits do: the air warms along the wall, rolls over the rim and mixes with the smoke. That is as far as we will go.
Why a smokeless pit is built to make ash
Look at the floor of one. It is a grate, or a plate with holes, over an ash pan. The design wants air moving up through the coal bed, because a coal bed with air under it burns hot and complete. The objective of a conventional fire pit is to make only heat, and biochar has a lot of energy in it, so it is designed to burn the biochar completely.
A flame-cap fire pit does the opposite on purpose. The bottom is solid. The only air is the air coming in over the rim, and the flames across the top use it up before it reaches the coals. So the coals stay as biochar, and you keep adding layers until the fire pit is full.[3] Then you put the fire out with water and keep the biochar you made in the fire pit. Same wood, same flames, except you are making two things: heat to enjoy and roast marshmallows over, plus biochar to nourish your garden.
What is left over
| Smokeless double-wall pit | Flame-cap fire pit | |
|---|---|---|
| What is left in the fire pit | Fine ash, a cup or two per evening. Alkaline, blows around, mostly minerals. | A pit of black biochar, several gallons. Stable carbon that keeps its shape and can enhance your garden's soil. |
| What you do with it | Empty the pan. A little ash can go on a lawn or a compost pile. | Drain it, mix it into your compost for a month, dig it into a bed. It stays in the soil for good. |
| How the fire ends | Burns itself out. Do not quench it with water; wait. | Flooded with water while the top is still glowing, from a hose connected to the bottom of the biochar kiln, or from the top when bottom-up quenching is not part of the kiln. Cool and wet in minutes. |
| Cleanup | Tip out the ash. Keep water out of the double wall. | Drain where it stands or run the hose to a bed. |
Heat and cooking
Where the heat goes. A double wall is insulation. The outer wall stays cooler, but it also means less heat comes out sideways to the people sitting around it. Most of it goes up. Some makers sell a deflector ring to reflect the heat back down. A single-wall fire pit radiates heat from its whole surface, so it warms your legs, not the sky. It also means the outside of the fire pit is hot, like a wood stove.
Cooking. Both types can be used for cooking. Smokeless pits take grates and griddles made for them. The fire pit takes a slotted grill or a solid griddle across the rim, and you cook over the flame cap after the flames have died down and you have a hot bed of biochar underneath. This is also a time to roast marshmallows.
Smokeless fire pit or flame-cap fire pit: which one to buy
| If you want | Buy | Because |
|---|---|---|
| The cleanest possible burning fire | A smokeless pit | It is built for exactly that. |
| To warm the people around the fire | The flame-cap fire pit | Single-wall steel radiates outward. Double wall sends the heat up. |
| Biochar for the garden | The flame-cap fire pit | See above. A smokeless pit is designed to make ash. |
| Something you never have to tend | Neither | Both need someone at the fire at all times for safety. The flame-cap fire pit needs a layer added each time the flames die down; the smokeless pit needs feeding too or it will die out. |
| A valuable byproduct for your garden | The flame-cap fire pit | The biochar comes out as a soil amendment to nourish your garden. |
Either pit, same rules. Check with your city, county or fire district that a recreational fire is allowed, whether you need a permit, and whether a burn ban is on. Level, fire-resistant ground, never a wooden deck, nothing overhanging, no wind. Dry, clean wood only. Someone at the fire the whole time.
Common questions
Do smokeless fire pits really not smoke?
They smoke less, a lot less, once they are hot and fed dry wood. They smoke on startup, on wet or oversized wood, and as they burn down. No wood fire is smoke-free.
Can I put water in a smokeless fire pit?
The makers say no. Water gets between the walls and into the vent holes, the ash turns to paste, and thin stainless can warp from the thermal shock. Let it burn out. A biochar kiln is built to be flooded, which is how it stops burning and makes biochar.
Is the ash from a smokeless fire pit good for the garden?
A little wood ash is a lime-like amendment that raises pH and adds potassium. It is not biochar, and it does not hold water or nutrients the way biochar does. Small amounts on a lawn or in compost are fine; keep it away from acid-loving plants like blueberries.
What is the best smokeless fire pit?
For a clean evening fire, any of the well-made double-wall pits: a Solo Stove smokeless fire pit, a Breeo, a Tiki, and the rest all work on the same principle, so pick by size, weight, and what accessories you want. For heat on your legs, or biochar at the end, the best option is a biochar kiln.
Can I build a DIY smokeless fire pit?
Yes, and people do: a steel drum inside a wider drum, holes around the base of the outer one and a ring of holes near the top of the inner one, with a grate under the fire. It works on the same principle as the store-bought ones.
Why is my Biochar-Making Fire Pit not smokeless?
Because no wood fire is, and we do not claim it. It works on the same principle as a double-wall pit, less aggressively: air warms along the outside of the slanted wall, rolls over the rim and mixes with the smoke so it burns off. Kept with a flame cap across the top it burns much cleaner than a pile or a conventional fire pit, and most of what you see is steam at the quench. Heavy smoke while making biochar means the wood is wet or you added too much at once.
Sources
- BioLite, How Smokeless Fire Pits Work: The Benefits of Double Combustion. A maker's own explanation of the double wall, the base and rim vents and the secondary burn. Read September 10, 2026.
- Family Handyman, Smokeless Fire Pit: What To Know Before You Buy. Startup and burnout smoke, and heat output. Read September 10, 2026.
- 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 and quenching.