thermodynamics - How to find the power required to maintain object temperature in a different-temperature environment?

For example, if I'd like to maintain a 1kg sphere of water at 50$\unicode{xb0}$C in a room full of air at 25$\unicode{xb0}$C, how much power must I put into the water as heat? Assume the room is large compared to the water.

I've found explanations and calculators for some specific cases. Most of what I'm finding has to do with the energy transfered as the temperature reaches equilibrium, but I don't know how to transfer that information to this question. I'm not even sure what search terms to use in a case like this where energy is being constantly put into the system.

I'd like to get enough of an understanding to understand the cases in which:

• The materials are different (e.g. steel ball in water, instead of water in air)


• There is a third material at the boundary (e.g. water in a rubber membrane in air)


• The shape is different (e.g. a planar interface, or an arbitrary shaped object)