Heat of combustion (HoC) is a key characteristic of fuels when analyzing and modeling wildfire scenarios. Despite significant differences in the structure of fuels from different environments, HoC is frequently considered a constant. This article briefly reviews methods used to describe natural fuels and the various different definitions of HoC. We also summarize measured values of HoC and elemental analyses of 238 plant genera reported in 28 papers since 1973. A statistical analysis of these data provided mean values and standard deviations of HoC for fuels according to six broad plant functional groups. Permutational Multivariate Analysis of Variance (PERMANOVA) demonstrated significant differences in the HoC with ground fuels and softwoods having particularly high values. Net heat of combustion was calculated for four fuel groups and the tabulated data may help to improve wildfire modeling and highlights fuels where further measurements of HoC are required.