Because rocks and ices viscosities strongly depend on temperature, planetary mantles and ice shells are often thought to be animated by stagnant-lid convection. Their dynamics is further impacted by the release of internal heat either through radioactive isotopes decay or tidal dissipation. Here, we quantify the impact of internal heating on stagnant-lid convection. We performed numerical simulations of convection combining strongly temperature-dependent viscosity and mixed (basal and internal) heating in 3D-Cartesian and spherical geometries, and used these simulations to build scaling laws relating surface heat flux, Φ_surf, interior temperature, T_m, and stagnant lid thickness, d_lid, to the system Rayleigh number, heating rate, H, and top-to-bottom viscosity ratio, Δη. These relationships show that T_m increases with H but decreases with Δη, while Φ_surf increases with H and Δη. Importantly, they also describe heterogeneously heated systems well, provided that the maximum dissipation occurs in hottest regions. For H larger than a critical value H_crit, the bottom heat flux turns negative and the system cools down both at its top and bottom. Two additional interesting results are that 1) while the rigid lid stiffens with increasing H, it also thins; and 2) H_crit increases with increasing Δη. We then use our scaling laws to assess the impact of tidal heating on Europa’s ice shell properties and evolution. Our calculations suggest a shell thickness in the range 20-80 km, depending on viscosity and dissipated power, and show that internal heating has a stronger influence than the presence of impurities in the sub-surface ocean.