Lesson 2.1 - Keeping Heat at Home

Have you ever noticed in the winter how some houses have lots of snow on their roofs and others have no snow?  Where did the snow disappear to?  Which house is better, the one with snow on the roof or the one with no snow?  You will find out more about snow on rooftops and more in this lesson. 

Read Keeping Heat at Home and R-Value on page 111 of your textbook. Then, answer the following questions.

Question 1. What is the purpose of insulation? 

Question 2. The information stated that insulation has two benefits.  It keeps the heat in during the winter, and it keeps the heat out in the summer.  How is this possible? 

Question 3. What is the difference between a good insulator and a poor conductor?

Question 4. Is air a good conductor or a poor conductor of heat? 

Question 5. What is the definition of R-value? 

Question 6. Which is a better insulator, a material with R-value = 10 or a material with R-value = 5? 

Question 7. What is the R-value of 25 mm of fibreglass? 

Question 8. What is the R-value of 75 mm of fibreglass? 

Question 9. What is the R-value of 50 mm of fibreglass and 50 mm of expanded polystyrene?

Question 10. Look at figure 6.4 on page 111.  Explain why the top of the roof on the house has no snow on it and large icicles hang from the eaves.

 

Check your answers with those that follow.

 

 

 

 

 

 

 

 

 

 

 

 

Answers to Questions:

Question 1. What is the purpose of insulation?

The purpose of insulation is to slow heat transfer.

Question 2. The information stated that insulation has two benefits.  It keeps the heat in during the winter and it keeps the heat out in the summer.  How is this possible?

In the winter, insulation slows the transfer of heat that is inside the house to the outside cold air.  Remember that heat transfers from hot to cold.  In the summer, insulation slows the heat transferring from the hot air outside to the cool air inside your house.  Although the transfer of heat is in opposite directions, insulation works in both winter and summer.

Question 3. What is the difference between a good insulator and a poor conductor?

There is no difference.  A good insulator and a poor conductor mean the same thing.

Question 4. Is air always a good conductor or a poor conductor of heat? 

Air can transfer heat very quickly if convection currents can be created.  If air can move freely, then it will be a good conductor.  If air is trapped so it is not free to move, it is a good insulator (a poor conductor).

Question 5. What is the definition of R-value? 

R-value is a measure of how well an insulating material slows heat transfer.

Question 6. Which is a better insulator, a material with R-value = 10 or a material with R-value = 5? 

The higher the R-value the better the insulator.  Thus, the material with R-value = 10 is the better insulator.

Question 7. What is the R-value of 25 mm of fibreglass? 

From table 6.2, the R-value of 25 mm of fibreglass is 4.25.

Question 8. What is the R-value of 75 mm of fibreglass? 

75 mm of fibreglass is three times as thick as 25 mm of fibreglass.  The R-value would be three times as much or 3 ? 4.25 = 12.75.

Question 9. What is the R-value of 50 mm of fibreglass and 50 mm of expanded polystyrene?

The R-value of 50 mm of fibreglass is 2 ? 4.25 = 8.50.  The R-value of 50 mm of expanded polystyrene is 2 ? 3.96 = 7.92.  The sum for both types of insulation is therefore 8.50 + 7.92 = 16.42.  The total R-value for the combination of the insulation is 16.42. 

Question 10. Look at figure 6.4 on page 111.  Explain why the top of the roof on the house has no snow on it and large icicles hang from the eaves.

The house does not have enough insulation in the attic.  The heat in the house rises and escapes through the roof and melts the snow.  The water runs down the roof and freezes into icicles before it can leave the eavestroughs. 


Go to the next page to continue Lesson 2.