There are three ways heat is transferred: Convection, Conduction and Radiation. Convection is heat transfer due to the movement of molecules within a fluid, such as air or water. The stack effect is a convective loop that causes a good portion of the heat loss during the winter. Conduction is heat transfer between neighboring molecules in a material. The wood or metal studs in a wall conduct heat from one side to the other. Thermal radiation is electromagnetic radiation emitted from an object, just like light but not visible to our eyes. The sun radiates heat, light and whole range electromagnetic energy. Our bodies also radiate to or absorb heat from our surroundings. Cold walls are like a heat sponge. They not only cool the air in the room by convection but they suck the heat out of you because you radiate your heat to the cold wall. The greater the temperature difference the more heat you loose through radiation.