Theoretical assessment of equilibrium moisture content influences on the fuel quality of salient firewood species in a humid subtropical climate zone: Insights from Lemondokop Village, South Africa

The daily dependence on firewood by households in developing countries creates continuous demand for fuel that often outpaces natural drying times prior to use. Given that high moisture content (˃20%) in firewood causes incomplete combustion, which is associated with adverse health impacts, this study assessed whether seasonal climatic variability theoretically supports firewood drying to acceptable fuel quality standards and how household storage practices influence this potential. Data were collected from 128 households using a structured questionnaire on preferred firewood species, storage practices, moisture content indicators, alongside regional climate data for the year 2025. The equilibrium moisture content (EMC) and net calorific value (NCV) were theoretically modeled under equilibrium assumptions to estimate the theoretical fuel quality under the prevailing climatic conditions. Three hardwoods: Dichrostachys cinerea , Combretum zeyheri , and Combretum apiculatum were most preferred. Outdoor uncovered storage dominated in both the dry (77%) and wet (67%) seasons. Climate analysis indicated that the prevailing climatic conditions possess the theoretical capacity to support high-quality fuel under equilibrium assumptions with NCV ranging from 15.63 to 16.68 MJ/kg, thus meeting ISO 17225–5 A1 classification in both seasons. However, continued reliance on outdoor uncovered storage, even in the wet season, increases the likelihood of moisture reabsorption and prolonged drying. Consequently, the realized fuel quality is likely constrained by storage practices more than environmental limitations. This highlights the need for climate-adaptive storage interventions to improve the combustion efficiency and reduce exposure to household air pollutants without reliance on costly technologies.