Flames over a wood element in quiescent air may be classified as (a) near-extinction, (b) stable-smokeless, and (c) smoky. The direct connection of these forms of flames with the surface gas flux (SGF) emitted from a pyrolyzing solid was investigated. Measurements were made on flames of wood pyrolysis gas issuing out of an 8.5-mm tube. For comparison, the same device and an 8.5-mm wick were used with kerosene, diesel and vegetable cooking oil. The ranges of the SGF for stable-smokeless flames were found to be quite narrow, indicating that improved combustion requires an increasing flame surface or keeping the SGF within a well defined range.