1. Heat loss and insulation

2. Heat loss from houses
A thermogram shows the distribution of heat over the surface of a house. It highlights where heat is being lost.
The white, yellow and
red areas are the warmest so these are the worst insulated parts of the house.
The blue and green areas are the coolest so these are the best insulated parts of the house.
A poorly insulated house loses more energy and so costs more to heat. It also means that more pollution particularly carbon dioxide is created in order to heat the house.

3. Heat loss from houses roof 20% walls 36% windows 12% doors 4%
floor 28%

4. Can heat loss through windows be reduced?
A lot of heat energy can be lost through windows.
Double glazing adds an extra pane of glass. The air trapped between the two panes acts as an insulator and reduces
heat loss by conduction.
insulating layer
of air
side-view
of double glazing
The insulating effect of the gap can be improved by removing the air and creating a vacuum.
The problems with double glazing are that it can be expensive and that it is difficult to break in emergencies without a special hammer.

5. How can heat loss through walls be reduced?
Most outside walls have an empty space between the two layers of bricks called a cavity.
convection currents
in the cavity
The air trapped in the cavity acts as an insulator and reduces any heat loss due to conduction through the bricks.
Heat loss can also occur due to convection within the cavity. Plastic foam insulation can be pumped into the cavity to prevent this.
foam insulation
prevents convection currents

6. How can heat loss through a roof be reduced?
The air warmed by radiators (and other heaters) is carried around a house by convection currents.
heat loss
The house becomes heated but if there is no roof insulation the warm air continues to rise.
The heat eventually escapes through the roof and is lost due to conduction through the roof tiles.
loft insulation
Loft insulation contains trapped air and so forms an insulating layer between the loft and the rest of the house. This helps to reduce loss through the roof.

7. How can heat loss from radiators be reduced?
A radiator produces infrared radiation.
Some of this heat energy is absorbed by the wall that the radiator is attached to and so the wall heats up.
This can be a real problem on outside walls where the heat energy absorbed by the wall can escape from the house.
Heat loss from a radiator can be reduced by placing shiny foil between the wall and radiator.
The foil prevents heat radiation from reaching the wall by reflecting it back into the room.
This method of insulation is very cheap to install.

8. How can heat loss through doors be reduced?
A draught is the movement of air due to a convection current.
A lot of heat energy can be lost from a house due to draughts escaping through gaps under doors and around windows. This is one of the easiest types of heat loss to prevent.
Draught excluders are hairy or spongy strips that can be used to close the gaps around doors and windows. They prevent draughts escaping and so reduce heat loss.

9. How can curtains reduce heat loss?
A draught is the movement of air due to a convection current.
Warm air rises and is carried up towards the windows in a house by convection currents.
This heat energy can escape through gaps around windows that are uncovered.
Fitting curtains and closing them can prevent draughts leaving a house and so reduce heat loss.
In addition, curtains are opaque and so radiated heat does not pass through them.

10. How does double glazing work?
How does double glazing keep a house warmer?
Double glazing keeps a house warmer because there is a layer of a__ between the panes of glass. ir
Air is a poor c________
so it acts as an i_______.
onductor
nsulator
The trapped air r_______ heat loss by c_________ from a house.
educes
onduction
side-view
of double glazing