saving energy by reducing heat loss

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Heat escape routes

Heat losses from a house Take a look at this diagram showing heat loss from a house.

Heat energy is transferred from homes through the

  • roof (conduction, radiation)
  • walls (conduction, radiation)
  • floor (conduction)
  • windows (conduction, convection, radiation))
  • doors (conduction & convection)

Examples of convective losses: cold air can enter the house through gaps in doors and windows, and convection currents can transfer heat energy in the loft to the roof tiles.

Heat energy also leaves the house by radiation through the walls, roof and windows.

Heat losses in a houseRed shows where most heat is lost - through the windows and roof

Ways to reduce heat loss

There are some simple ways to reduce heat loss, including fitting carpets, curtains and draught excluders.

Heat loss through windows can be reduced using double glazing. There may be air or a vacuum between the two panes of glass. Air is a poor conductor of heat, while a vacuum can only transfer heat energy by radiation.

Heat loss through walls can be reduced using cavity wall insulation. This involves blowing insulating material into the gap between the brick and the inside wall, which reduces the heat loss by conduction. The material also prevents air circulating inside the cavity, therefore reducing heat loss by convection.

Heat loss through the roof can be reduced by laying loft insulation. This works in a similar way to cavity wall insulation.

Pay-back time

If some heat escapes from the house, it costs money and wastes resources. In deciding how cost-effective an energy-saving measure is, we need to know what its pay-back time is. In other words, taking the example of double-glazing: how long will it take before the cost of having the double-glazing installed will be recovered by what we save in fuel bills? The calculation is:

pay-back time in years  =  cost of energy-saving measure  ÷  money saved each year

Example

Double-glazing might cost £2,500 to install and save £100 a year in fuel bills. What is the pay-back time?

pay-back time = cost of energy-saving measure ÷ money saved each year
= 2,500 ÷ 100
= 25 years

 

[ This page has been adapted from www.bbc.co.uk/schools/gcsebitesize/science ]