Use a rocket stove indoors only if the exhaust leaves the room through a chimney pipe to the outside, because even clean-looking combustion produces carbon monoxide. Cross-ventilate the room as well, with an opening that lets air in and a second one that lets it out; a single cracked window is not enough. Without an exhaust path, do not use the stove inside at all.
Part of Rocket Stove Design
A stove in a room consumes the room’s air and puts its exhaust into it unless the exhaust is piped out. Both the pipe and the air supply have to work.
Two Separate Jobs: Exhaust Out, Fresh Air In
The overview states the rule: rocket stoves can be used indoors only with proper ventilation; the exhaust must exit through a chimney pipe to the outside; a rocket mass heater’s exhaust travels through the thermal mass and exits via chimney; never use one indoors without an exhaust path, because even smokeless combustion produces carbon monoxide.
- Exhaust. A sealed pipe, rising and ending above the roof, with no leaks at joints. Check joints for smoke when the stove first burns.
- Fresh air. The stove draws air from the room. Provide an inlet low on one side and an outlet higher on the other, so air moves across the room. One cracked window mostly trades air through a single gap.
When The Draft Fails
A cold chimney has no lift, and wind, a closed door or a second fire can pull the flow backward. Warm the chimney before you light, watch the feed opening for smoke, and treat any smoke in the room as a stop signal. For the size of the draft, see The Chimney Effect: a 30 cm riser’s pull (about 2.4 Pa in the worked example) is the same size as the pressure of a 2 m/s breeze.
Common Mistakes
- Closing every opening to keep heat in. That removes the fresh air.
- Believing a stove with no visible smoke needs no exhaust. Carbon monoxide is invisible.
- Sleeping in the room while the fire or embers burn.
- Closing the chimney while embers glow. Embers keep making carbon monoxide.
Safety
Indoors, the exhaust is the danger
Carbon monoxide has no smell and no colour; headache, nausea and drowsiness feel like ordinary tiredness. Feeling sleepy near a burning stove is a reason to get out and ventilate, not to lie down. A flame cannot test the air: it burns normally at concentrations that kill. A salvaged battery carbon monoxide alarm is worth having, but it does not replace a sealed exhaust. See Carbon Monoxide Risks.
What’s Next
- Learn next: Carbon Monoxide Risks — the hazard with numbers
- Combine with: Heating Systems — placing a stove in a shelter