A wick selection rule for tallow and beeswax candles

A candle fails in two opposite ways. If the wick is too small for the candle, its flame melts only a narrow well in the centre, the walls never melt, and the flame sinks into a tunnel of its own making. If the wick is too large, its flame melts a pool wider than the candle, the liquid overflows, the flame is fed faster than it can burn cleanly, and the candle smokes and drips. This paper states a heat-balance model that predicts melt-pool diameter from wick burn rate and wax properties, converts that prediction into a selection rule with computed failure bounds on both sides, and tabulates the rule for tallow and for beeswax. The energy needed to melt a kilogram of wax, at 20 °C ambient, is 234.0 kJ/kg for tallow and 280.0 kJ/kg for beeswax, a ratio of 1.197. At the same wick class, W3 at 7.0 g/h, the predicted pool is 36.9 mm in tallow and 29.8 mm in beeswax, a reduction of 19.2%. The practical consequence is that a wick chart for one wax does not transfer to the other: a 50 mm candle is correctly served by W4 in tallow but needs W5 in beeswax, and candles of 20 mm in tallow and 80 mm in either wax fall outside the five classes considered altogether. All results are model calculations. SIMULATED, NOT MEASURED.