Variability in the household use of cooking fuels: The importance of dishes cooked, non-cooking end uses, and seasonality in understanding fuel stacking in rural and urban slum communities in six north Indian states

•Despite widespread cooking gas availability and use, biomass use for cooking and heating remains prevalent in six energy poor north Indian states.•We observe wide variations in the way households with the same primary and secondary cooking fuels use their secondary fuels.•About 40% of rural and urban slum households used biomass for some non-cooking energy end uses, especially space heating and heating bath water.•Three-quarters of fuel stackers reported switching their primary cooking fuel across seasons of the year.•Detailed surveys of household cooking fuel end use offer insights into the important roles played by biomass in households.