Volume heating rates and their most relevant contributors (>5% of H_tot at each specific r) calculated for the hot 5M_⊕ sub-Neptune under moderate XUV irradiation. The top, middle, and bottom panels present the results of model#1 (pure hydrogen atmosphere), model#3 (hydrogen+helium), and model #5 (solar composition), respectively. The processes responsible for the heating and the corresponding line styles are given in the legend located above the top panel and with the following notation: H_tot – total volume heating rate from all sources; Hlin – iso-sequence line heating; H i – heating due to photoionisation of atomic hydrogen; Hion – collisional ionisation heating (all hydrogen species); H- – H⁻-heating; Hn = 2 – photoionisation from all excited states of hydrogen species; H2ph – H₂ photoionisation heating; H2vH – heating by collisional de-excitation of vibrationally excited H₂; H2dH – heating by photodissociation of H₂ ; He ii – photoionisation of Hen; He i – photoionisation of He i; ChaT – charge transfer heating; Can – metal line heating dominated by absorption of the Can line at 7291.47 Å; O i – photoionisation of O i; Fe i – photoionisation of Fe i.