This Skeptical Science article explains that geothermal is very small, $0.09W/m^2$, compared to radiant heat flows. It also does not change much in time, so it can be neglected in climate change calculations.

For an airless planet the equilibrium temperature $T$ can be calculated from $$ F=\sigma T^4$$where $F$ is the average absorbed heat flux at the surface and $\sigma$ is the Stefan-Boltzmann constant. If there is an additional internal flux $I$, the equilibrium temperature is increased by $\Delta$: $$F+I=\sigma(T+\Delta)^4$$ For small $I$ this leads to $$\Delta \approx \frac{TI}{4F}$$ With or without the atmosphere, $I$ is three orders of magnitude smaller than $F$, so $\Delta$ is a fraction of a degree.

This Skeptical Science article explains that geothermal is very small, $0.09W/m^2$, compared to radiant heat flows. It also does not change much in time, so it can be neglected in climate change calculations.

For an airless planet the equilibrium temperature $T$ can be calculated from $$ F=\sigma T^4$$where $F$ is the average absorbed heat flux at the surface and $\sigma$ is the Stefan-Boltzmann constant. If there is an additional internal flux $I$, the equilibrium temperature is increased by $\Delta$: $$F+I=\sigma(T+\Delta)^4$$ For small $I$ this leads to $$\Delta \approx \frac{TI}{4F}$$ Without the atmosphere, $I$ is three orders of magnitude smaller than $F$, so $\Delta$ is a fraction of a degree. I don't think the atmosphere would amplify this effect.