1. Heat loss from houses

2. Energy in the home
We lose energy from the roof, the door, the walls and the windows.
In order to reduce electricity bills and pollution, we need to keep energy losses from our homes to a minimum.
There are lots of methods we can use to reduce the rate of heat loss.

3. Reducing Heat Loss
We lose energy from the roof, the door, the walls and the windows.

4. Methods of Insulation
Most methods of insulation rely on one of four facts…
Non-metals are good insulators
Liquids and gases are good insulators
Conduction requires particles to transfer heat i.e. there can be no conduction across a vacuum
Trapping air bubbles close to a surface prevents heat loss by conduction because the pockets of air act as insulators

5. 1. Cavity Walls
Most outside walls have an empty space between the 2 layers of bricks called a cavity.
This reduces heat loss by conduction through the bricks.
How does a cavity wall prevent heat loss from a home?
Heat energy reaches the interior wall
The heat energy is conducted through the wall
The air cavity between the two walls in a cavity wall acts as an insulator and reduces heat loss by conduction

6. 2. Foam-filled Cavity Walls
Cavity wall foam insulation can be pumped in between the bricks to prevent convection within the cavity.
How does a foam-filled cavity wall prevent heat loss from a home?
Heat energy reaches the interior wall
The heat energy is conducted through the wall
The foam in the cavity wall reduces heat loss by convection currents in the cavity wall. Also the pockets of air in the foam act as extra insulation

7. 3. Double-glazing A great deal of energy is lost through windows.
Heat energy reaches the interior pane of glass and is conducted through the glass.
By adding an extra pane, the trapped air in between acts as an insulator to reduce heat loss by conduction.
The insulating effect of the gap can be improved further by sucking all the air out to create a vacuum.
Double glazing is expensive and difficult to smash without a special hammer.

8. 4. Curtains
Curtains reduce draughts [convection currents] leaving the house. They are opaque and so don’t allow much radiated heat to pass through them.

9. Heat loss prevention - draughts
Draughts are convection currents.
A great deal of heat energy is lost in this way but it is the easiest type to prevent.
Draught excluders are hairy or spongy strips which close gaps and prevent the convection currents escaping.

10. Heat loss prevention - roof
The air heated by central heating is less dense than the cooler air around it and rises.
The ceilings get heated and eventually the heat escapes through the roof.
Loft insulation contains trapped air which forms an insulating layer between the rooms and the attic.

11. Heat loss prevention - radiators
Radiators heat the wall a great deal - this wastes heat energy.
Placing shiny silver coated card between the wall and the radiator reduces heat loss by radiation by reflecting it back into the room.

12. Energy loss prevention
Complete the table below to show how various types of insulation prevent heat energy loss from our homes.