PrintHeat escapes (or transfers) from inside to outside (high temperature to low temperature) by three mechanisms (either individually or in combination) from a home:
- Conduction
- Convection
- Radiation
Click here to open a text description of the examples of heat transfer by conduction, convection, and radiation
Conduction
Conduction is a process by which heat is transferred from the hot area of a solid object to the cool area of a solid object by the collisions of particles.
In other words, in solids the atoms or molecules do not have the freedom to move, as liquids or gases do, so the energy is stored in the vibration of atoms. An atom or molecule with more energy transfers energy to an adjacent atom or molecule by physical contact or collision.
In the image below, heat (energy) is conducted from the end of the rod in the candle flame further down to the cooler end of the rod as the vibrations of one molecule are passed to the next; however, there is no movement of energetic atoms or molecules.
Click the play button to start the animation.
Click here to open a text description of the Conduction Candle animation
With regard to residential heating, the heat is transferred by conduction through solids like walls, floors, and the roof.
Click the play button to start the animation.
Click here to open a text description of Conduction in Regard to Residential Heating example
Convection
Convection is a process by which heat is transferred from one part of a fluid (liquid or gas) to another by the bulk movement of the fluid itself. Hot regions of a fluid or gas are less dense than cooler regions, so they tend to rise. As the warmer fluids rise, they are replaced by cooler fluid or gases from above.
In the example below, heat (energy) coming from candle flame rises and is replaced by the cool air surrounding it.
Click the play button to start the animation.
Click here to open a text description of the Convection Candle animation
In residential heating, convection is the mechanism by which heat is lost by warm air leaking to the outside when the doors are opened, or cold air leaking into the house through the cracks or openings in walls, windows, or doors. When cold air comes in contact with the heater in a room, it absorbs the heat and rises. Cold air, being heavy, sinks to the floor and gets heated, and thus slowly heats the whole room air.
Instructions: Press the play button below and observe what happens to the cold air (blue arrows) as it enters the house and encounters the warm air (red arrows) coming from the heating vent:
Click here to open a text description of the Convection in a Room animation
Radiation
Radiation is the transfer of heat through electromagnetic waves through space. Unlike convection or conduction, where energy from gases, liquids, and solids is transferred by the molecules with or without their physical movement, radiation does not need any medium (molecules or atoms). Energy can be transferred by radiation even in a vacuum.
In the image below, sunlight travels to the earth through space, where there are no gases, solids, or liquids.
Click the play button to start the animation.
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Test Yourself
First, identify the type of home heat loss pictured in images A-J as either: conduction, convection or radiation. Then click and drag each image down to the correct category at the bottom of the screen.
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Reducing Energy Consumption
There are two ways in which we can reduce energy consumption.
- The most cost-effective way is to improve the home’s “envelope”—the walls, windows, doors, roof, and floors that enclose the home—by improving the insulation (conduction losses) and sealing the air leaks with caulking (convection losses).
- The second way to reduce the energy consumption is by improving the efficiency of the furnace that provides the heat.
Click here to open a text description of the Conduction and Convection diagram