Heat is in constant motion. It flows from warmer areas to colder areas until an overall equal temperature is established. Heat moves from one place to another in three ways.

Conduction is the movement of heat through a substance or between substances in contact with each other. In such cases, heat moves directly from one molecule to another molecule in contact with it. Conduction is involved, for instance, when heat travels from the burner to a metal pan on the stove. In a home, insulation is used to minimize heat movement by conduction.

Convection is the movement of heat by the actual movement of a heated gas or liquid. For example, warm air or water is less dense than cooler water or air and therefore rises, while cold, more dense, air or water falls. This is the mechanism for lifting hot air balloons. As air is heated, it becomes less dense and rises into the balloon. Because air contained in the balloon is less dense than the surrounding air, it rises off the ground. In homes, a special case of convection known as infiltration occurs when air moves into and out of the home through cracks and other openings in the envelope.

Radiation is the movement of heat away from an object by means of electro-magnetic waves or infrared rays. This process involves only the molecules of the substance radiating the heat. Radiation can occur through a vacuum and is the mechanism by which the heat of the sun is transferred to earth. If you sit in front of a hot stove or fire you will feel the radiated heat.