Chances are, your algebra teacher was wrong when they swore up and down that you would use algebra in your daily life. But your physics class, on the other hand…
Keeping a house warm in the winter and cool in the summer is an ongoing challenge, a demonstration of physics in action. We all know how our homes react to the different seasons, based upon our daily experiences. But why does the kitchen get hot when the sun shines through the window? Why does the basement seem to suck the heat right out of your living room floor?
Because physics. There are many types of energy that we use every day: the electrical energy you draw from the wall outlet, the kinetic energy of your movement as you walk through the house, the chemical energy released from the food in your stomach, the compression waves we create in the air every time we speak. These are all forms of energy. And heat is another type of energy, known as thermal energy.
So why is this blog post turning into a physics lecture? Because, understanding the basics of how thermal energy (heat) is transferred and transmitted through your home will allow you to find ways to more economically keep your home cool in the summer, and warm in the winter.
What it comes down to is, there are three major ways that heat energy is transferred within your home. Today, we’re going to cover the most common form of heat transfer in a home: conduction.
Why Understanding Conduction is Important to Homeowners or Prospective Buyers
It’s not important to know the numbers or equations that describe how conduction works in detail. But it’s a good idea to have a basic understanding of how conduction works, when it comes time to redo the walls of your home or you go looking for a new home. A home built with the properties of conduction in mind will be a lot less expensive to keep warm or cold than a home that isn’t.
Perform This Simple Action to Experience Conduction Firsthand
Conduction is the transfer of heat through solid objects. The next time you’re cooking dinner and have a pot of boiling water on the stove, grab a knife from the silverware drawer and place the blade end in the boiling water, while you hold the handle. In a minute or so, the handle will become warm. Hold it for a few minutes, and it’ll begin to burn your hand. It makes sense that the blade would be hot, since it’s in direct contact with the water. But why does the handle get hot?
This is where conduction comes into play. The metal blade of the knife absorbs some of the thermal energy in the boiling water, and that energy slowly spreads up the knife. That happens because heat is actually the vibration of the atoms that make up an object. If an object’s atoms are vibrating really fast, then it’s hot. If an object’s atoms move slowly, then it’s cool. Heat always shifts from warmer areas to cooler areas. But how does this transfer happen?
Think of Conduction as a Crowd at a Rock Concert
Imagine a noisy rock concert, with a big audience in front of the stage. The audience is split into two halves. The front half is made up of all the crazy high energy folks jumping up and down, screaming. The back half is made up of all the folks who would rather chill and relax. The people up front bounce off of each other constantly. The people in back stay still. But what happens at the point where the two groups meet?
The chill people who keep getting bumped into by the active folks are constantly getting jostled around. They aren’t moving as much as the majority of the high energy folks, but like it or not, they’re moving with the groove a bit. The people behind them get jostled a little bit, and so on a few more layers back into the audience.
Meanwhile, the active folks bumping into the chill people aren’t going to have the same freedom of motion that their neighbors closer to the stage have. Their movement is restricted and diminished, because some of that boisterous energy is transferred to the sedate half of the crowd.
This is similar to what the atoms in the knife are doing. The really excited atoms in the heated blade of the knife keep slamming into less energetic atoms closer to the handle, transferring some of the energy in the process. And this continues on in a chain reaction, all the way up the handle. That is the process of conduction—the transfer of thermal from one atom to the next. It happens in all types of matter: solid, liquid, and gas.
Conduction in Your Home
Conduction happens in every home on Earth. When it’s warm outside, the atoms that make up the outside air slam into the atoms that comprise the walls and roof of your home. That energy gradually penetrates through the wall, up to where the inside surfaces of the walls meet the air. There, the atoms of the walls smack against the atoms in the air inside, and gradually, the air in your house warms up. This process reverses itself when it’s warmer inside your house than it is outside. The inside air warms the walls, which in turn warms up the outside air.
However, some things don’t transfer heat as well as others, because of how their atoms are arranged. We call these materials insulators. The wood in the walls of a house and the air inside and outside of it are actually considered insulators because they don’t transfer energy very efficiently compared to, say, metal or water. (This is why a high-quality Thermos is double-walled—the air between the two layers inhibits the transfer of heat between the contents and the outside air). But, there’s a LOT of air in the great big outside, and a lot of surface area where it contacts the walls and roof of your home, so heat still manages to transfer through.
But other types of material are even better insulators than wood or air. That’s why most homes don’t just have hollow walls, or solid wood walls. Instead, we stuff material in between the inner and outer walls of a home that happens to be very bad at transferring thermal energy. These are the insulators you find in your local hardware store—fiberglass, foam board, rock-wool, polyurethane foam, (and in the past, asbestos). Dual pane windows are also a type of insulation, as the layer of air between the two panes partially inhibits the transfer of heat energy.
The Bottom Line
This is why it’s important to invest in high quality insulation and windows that keep thermal energy where you want it to be: outside of your home in the summer, and inside your home in the winter. You can see how effective an insulation is by looking at its “R-value.” The R-value indicates just how resistant a material is to thermal transfer, compared to how thick it is. The higher the R-value, the better. The R-value of an inch of fiberglass insulation is a bit more than three times the R-value of an inch of solid wood. That means that one centimeter of fiberglass is a slightly better insulator than three centimeters of fiberglass.
Remember: Don’t worry about forgetting algebra, but DO remember your physics!
