The concept of heat is simple enough. We feel it when we sit in front of a fire, clutch a cup of hot tea or soak in a warm bath. And we see it in action when we leave a hot or cold drink on the counter for too long. A hot drink eventually loses its heat as it’s absorbed by its cooler surroundings, and a cold drink slowly gets warmer as it absorbs the heat from its surroundings. In short, if you leave food or drinks out long enough, they’ll all end up room temperature. That’s because heat is energy that transfers from a higher-temperature object or medium to a lower-temperature object or medium. However, the way in which the heat transfers varies.
There are three types of heat transfer: radiation, convection and conduction.
Radiation heat uses electromagnetic waves to transfer heat. All materials absorb and emit radiation. This is how the sun heats the earth and why we feel warmer when standing close to a fire. Without physically touching anything, you can feel radiant heat just by being in its pathway. This is the same way radiant heating systems for houses work. Whether it’s radiant floor heating, a radiant panel or a towel warmer, these systems use electromagnetic waves to transfer their heat to the people and objects in a room.
If you’ve ever heard the expression “hot air rises,” that in a nutshell is the concept of convection heat. Convection heat uses the movement of liquids or gases to transfer heat from warmer areas to cooler areas. For instance, forced-air systems are a form of convection heat. Heat is generated in the furnace then distributed throughout the house via a ventilation system. As the warm air blows through the vents at the floor, it rises, forcing the cooler air downward. The same concept applies to liquids. When you boil a pot of water, you’re seeing convection heat as the hotter water bubbles up to the surface, where the cooler water resides. In both cases, the movement of liquids or gases circulates heat throughout the area.
Conduction is the only type of heat transfer that uses direct contact. By definition, it is the transfer of heat from one solid to another of a different temperature. Essentially, any time you’ve touched an object hotter or colder than your own body temperature, you’ve experienced conduction. When you pick up a hot cup of coffee, heat from the cup warms your hands. Alternately, when you step onto a cold tile floor, you lose some of your body heat as it transfers to the tile. Conduction also is at play when you immerse yourself in a warm bath or shower.
These types of heat transfer can occur by themselves or altogether. For instance, when you boil a pot of water on the stove, the stove heats the pot via radiation; the water boils via convection; and your hand is warmed by the pot handle via conduction.
During the winter months, homes use either radiation or convection heat to keep homeowners warm. To learn more about the differences between these two types of heat as they pertain to home heating, check out this blog.