Convection occurs when heat is transferred by the mass movement of molecules from one place to another. Rate of heat transfer is proportional to the area in contact and the temperature differerence. , where h is the thermal convection coefficient for the particular case.
Conduction occurs from molecular collisions when there is a temperature difference.
Fourier 's equation for heat conduction. Rate of heat transfer is proportional to the cross-sectional area and the temperature differerence and inversely proportional to the thickness. , where k is the thermal conduction coefficient for the conducting medium. Radiation occurs with electromagnetic waves which transfer heat without the need for the presence of matter. Stefan-Boltzmann 's equation for heat radiation. When air is free to flow under a house, any hot air will flow out and cooler air will flow under the floor.