From olden fire pits to today’s central heating, humans have worked hard at making the place they call home comfortable. The physics of heat plays an important part in a comfortable home — if you manage it well.
Heat is a kinetic energy. Others are mechanical, chemical, electrical, and electromagnetic. These other “moving energies” create heat by stimulating molecules in matter to move faster. As the molecules pick up speed, they bounce off one other, like pool balls scattering at the game’s opening break. When they careen around fast enough, they create heat. Consider heat something like an amplifier for moving molecules. As you turn the heat amplifier up it gets hotter. This changes the molecule’s stable condition into chaotic movement and they start ricocheting off one another faster as the heat increases.
The physics of heat is the same, no matter its source. However, for a house, you can get heat by burning something (for example, wood, coal, oil-based products, or propane). Or, you can pass electricity through a resistive filament (or coil) to agitate its molecules into moving so quickly and randomly they make it glow like those in your toaster. Heat occurs whenever some other form of energy excites molecules to move faster.
The common belief “heat rises” is a partial truth. Heat always flows from where it is (a high-temperature area) to where it isn’t (a low-temperature area) whether that’s up, down or sideways. Heat moves three ways — conduction, radiation and convection. All three are at work in your home. Understanding these movement patterns helps make your home more comfortable and limits heat loss.
Conduction is the main way energy moves in a house. As your heating system warms your home, the walls, ceiling and floors may conduct heat to attics and crawlspaces, whenever these places are cooler. If these areas are insulated, less heat moves out of your living space, keeping it comfortable (and lowering your heating cost). During the summer, when the home inside is cooler, heat will move into it. Even small cracks, like those around electrical sockets, can let heat in or out, usually in the opposite direction you’d intend. Small foam pads behind the sockets isolate the cracks and stop the heat loss.
Stand near a window on a sunny day and you’ll feel warm because the sun radiates heat through the window onto you. During the winter, you can let the radiant energy outside into your home by opening the window coverings on the east side in the morning and on the west in afternoons. Summertime, your house may receive too much radiant sunlight beating through the windows and on the outside of your house. Then simply close the blinds to block it. Light-colored houses and light-colored roofs also reflect unwanted heat in the summer when you don’t need it and are common in warm, sunny climates.
Convection is a heat transfer through a liquid (like water) or a gas (like air). In your home, convection can occur within your walls or in the attic. Unsealed areas between framing studs and gaps can cause heat convection. The same may occur in an attic. Convection creates a mini-environment circulating air and pulling heat from your home. That’s why today, many green builders take the extra time to seal the outside frame and create barriers that block the airflow before installing any insulation. Older homes with insulated outer walls also lose less heat through convection.
For homey comfort, you want an evenness of temperature throughout your house. From a homeowner’s perspective it makes sense to control all types of heat transfer by insulating outer walls, under floors and in the attic to slow heat transfer and keep living spaces cozy and warm.
Energy Adviser is written by Clark Public Utilities. Send questions to firstname.lastname@example.org or to Energy Adviser, c/o Clark Public Utilities, P.O. Box 8900, Vancouver, WA 98668.