Energy can be transferred by heating in 3 ways: CONDUCTION, CONVECTION and RADIATION.

Conduction is when heat is transfer between objects which are touching. Energy is always transferred from objects which greater thermal energy to objects with less thermal energy. Everything has thermal energy, except things that are at absolute zero. The particles touch and the vibrations are transferred across the substance

Objects which can conduct thermal energy quickly are called conductors and objects which can't are called insulators. Metals are good conductors of thermal energy because they have delocalised electrons which can carry thermal energy throughout the structure, increasing its temperature quickly. Air is an insulator because there a large gaps between the particles, so its harder for them to transfer the energy from one end to another.

Radiation is energy transfer between objects which aren't touching. Space is a vacuum yet the sun's energy reaches us. This is via infrared radiation. Different objects can absorb or emit IR better than others. Matte black objects are the best IR absorbers and emitters and shiny white objects are the worst IR absorbers and emitters.

A black body is a theoretical object which is the perfect absorber and emitter of all types of radiation.

Different objects emit different amounts of different types of radiation. Our Sun emits lots of light and IR whereas a hotter star would emit more UV. As the temperature of an object increases, the intensity of radiation it emits is greater at every wavelength. It's peak wavelength gets shorter and shifts to the left of the graph. The shorter the peak wavelength, the greater the increase in intensity of the wavelength.

Specific Heat Capacity is the amount of energy required to raise the temperature of a kilogram of a substance by one degree Celsius. Its calculated using:
E = m x c x t

If an object has a high SHC, then it requires a lot of energy to raise it's temperature. water has a very high SHC so that's why even in sunny places, the water is always very cold.

Buildings in hot countries are usually painted white. This is because white is the worst absorber of IR, so the house won't become hot.

Double glazed windows have 2 layers of glass with a layer of air in between them. Air is a very good insulator, and so is glass, so the house won't lose thermal energy through its windows.

In theory, radiators would work best if they were painted black and had reflective surfaces behind them to reflect IR back into the room.