Heating and cooling contributions in the atmosphere of KELT-20b/MASCARA-2b. Top: contribution to the total heating as a function of pressure. At each pressure bin, the plot shows the three most important heating processes. The main heating processes occurring in the middle and upper atmosphere are hydrogen photoionisation (red; photoionisation of HI lying in the ground state), metal line absorption (blue), H⁻ absorption (green), photoionisation of hydrogenic species (photoionisation of excited HI; magenta), and collisions with H₂ (brown). Bottom: contribution to the total cooling as a function of pressure. At each pressure bin, the plot shows the three most important cooling agents.