Lesson 7 — Activity 2: Keeping Your Home Warm
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Lesson 7 — Activity 2: Keeping Your Home Warm
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During Canadian winters, we are always interested in the amount of heat in our homes. Unfortunately, heat can leak out through doors, windows, roofs, and walls. Proper insulation can help with this as insulation slows heat transfer. You will learn about insulating a house in this activity and also learn that a knowledge of heat transfer is also used to keep things inside your house warm.
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Good insulation gives you two benefits for the price of one. Insulation that keeps heat in during the winter also keeps heat out on a hot summer day. Having a knowledge of heat transfer will enable you to keep your home warm in the winter and cool in the summer. What makes a good insulator?
R-value
Air transfers heat when it is moved by convection currents. Air is an excellent insulator when it is held still, but when it is moving, an insulating material that slows heat transfer is needed.
R-value is a measure of how well an insulating material slows heat transfer. Materials with high R-values such as urethane foam are better insulators than those with low R-values, such as bricks or concrete. An insulation of R-12 loses heat faster than one with R-16. When materials are used together, the total R-value is the sum of the R-values of each material used. Click below to see a table with the R-values of some common building materials.
Here's an example:
The walls in your home have 25 mm of solid wood and 25 mm of rigid urethane foam. What is the R-value of your insulation?
1. Check the R-value of 25 mm of solid wood.
2. Check the R-value of 25 mm of rigid urethane foam.
3. The total R-value of these two materials would be:
1.25 + 7.50 = R 8.75
Doors and Windows
Doors
and windows are two weak points when you try to keep a house warm. A
single pane of glass is a poor insulator as heat escapes quickly through
glass. Leaks also develop around the panes and around the edge of the
windows.
Older
houses use double doors and windows — called storm doors and storm
windows — to keep heat in. Today’s exterior doors and windows use double glazing. This provides a space of still air. The space between the
panes of glass is filled with a mixture of air and a gas called argon.
This slows the transfer of heat.
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Exterior doors used to be solid wood. Modern
doors are cavities filled with insulation. Some are
metal covered. To prevent heat transfer, there is a
break in the metal between inside and outside.
Did you know that if you have a crack of only 1.5 mm around the outside of one window, your furnace may burn an extra litre of fuel per day?
Try This:
Tape a piece of magnetic tape to a short stick. Hold this breeze detector near the crack of a window. If the tape moves in a draft, heat is leaking out of your building.
A knowledge of heat transfer is also used to keep things in your house warm.
A vacuum bottle, usually called a thermos, uses several of the same technologies that keep your house warm in order to keep food and beverages warm. A thermos works by insulating the food and liquids placed inside.
Look at the picture on the right. Surrounding the food is a glass bottle that has been coloured silver so it acts like a mirror and reflects any heat energy trying to move inside. That glass bottle is special; it has a vacuum. That is, the air pressure in it is less than the air pressure around us. This hinders the movement of heat (or cold) away from the contents.
Next there is an area where there is nothing! No atoms of any sort — just empty space. This is known as a vacuum. Because this space is empty, there can be no transfer of heat.
The plastic in the foam in the outer case is a very poor conductor of heat, so it also helps reduce heat loss.
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