A Household Cookstove Smoke Witness and Chimney-Draft Design Bound: What a Sub-US$20 Carbon Monoxide Witness Can Resolve, and the Flue Dimensions That Keep a Cooking Fire's Smoke Out of the Room

Design study (SIMULATED, NOT MEASURED). A low-cost electrochemical carbon monoxide witness with a US$19.80 volume bill of materials cannot certify compliance with the WHO 24-hour CO guideline of 4.0 mg/m3: its uncertainty at the guideline is 2.33 mg/m3 and its smallest resolvable 24-hour exceedance is 2.3 times the guideline, though it works as an alarm at cooking-peak concentrations. A 0.15 m diameter, 3.5 m flue, costed at US$49.10, exhausts a 3.0 kW flue-connected cooking fire at the design flow in calm air and against a 5 m/s adverse wind, and fails at cold start, at low fire on a hot day, and against an 8 m/s adverse wind, where the witness is the only protection.