Complete combustion turns the gases from wood into carbon dioxide and water and releases all their heat, whereas smouldering leaves unburned gas, soot and carbon monoxide. A well-running rocket stove makes almost no visible smoke after its first minute; persistent smoke, a sooty pot or a lazy dark flame means the burn is incomplete and carbon monoxide is being made.
Part of Rocket Stove Design
A fire burns completely when wood gases reach carbon dioxide and water, and smoulders when they escape as smoke, soot and carbon monoxide. The difference shows in the smoke, the soot and the flame.
Carbon Monoxide Is Half-Burned Fuel
Carbon in wood burns to carbon monoxide (CO) on its way to carbon dioxide (CO₂). Whether it finishes depends on temperature, enough air and enough time in the hot zone. Cool the flame on a cold surface, starve it of air or crowd it with wet fuel, and the burn stops at CO or leaves smoke. The overview puts it this way: a smouldering fire releases energy as unburned gases, visible as smoke, whereas the insulated chamber keeps temperatures high enough for these gases to ignite and release their energy as heat. The overview also says that a well-running rocket stove produces almost no visible smoke after the first minute of start-up.
Reading The Fire
| Observation | Meaning |
|---|---|
| Steady roar, short bright flame at riser top, almost no smoke | Burning completely |
| White steam and hissing from the sticks | Wet fuel; see Smoke Troubleshooting |
| Grey or black smoke | Unburned gas; incomplete |
| Black soot on the pot | Flame cooled on the pot; incomplete |
| Pale blue flicker over glowing coals | Carbon monoxide itself burning, so it is being made |
| Smoke at the feed opening | Draft reversed or blocked; leave the area |
A blue flame is not a sign of a clean wood fire. Over hot coals it is the sign of carbon monoxide burning.
Why Start-Up Is The Dirty Part
A cold chamber has no insulation benefit yet. Light the fire, feed thin dry sticks and give the riser time to heat. The overview says to wait 30 to 60 seconds for the draft to establish.
Common Mistakes
- Judging the burn only by flame size. Judge by smoke and soot.
- Overloading the magazine. It chokes the air.
- Cooking in the start-up smoke. The first minute is the worst.
Safety
You cannot smell carbon monoxide, and a flame will not detect it
Carbon monoxide has no smell and no colour. Headache, nausea and drowsiness feel like tiredness. Feeling sleepy near a burning stove is a reason to leave and ventilate, not to lie down. A flame burns normally at concentrations that kill, so do not test the air with one. Use stoves outdoors, or exhaust them outside. See Carbon Monoxide Risks.
What’s Next
- Learn next: Materials & Construction — building the stove
- Combine with: Starting & Feeding — a clean start