Take a look at this thermogram of a house. Its roof and windows are the hottest, showing that most energy is lost from the house that way.
Energy is transferred from warm homes to the outside by:
There are some simple ways to reduce energy transfers from a house, including fitting:
Double glazing involves having two panes of glass in the window instead of just one. There is air or an even better insulator such as argon gas between the two panes of glass. This reduces energy transfer by conduction.
Energy loss through walls can be reduced using cavity wall insulation. This involves blowing insulating material into the gap between the outside wall and the inside wall to reduce conduction. Loft insulation works in a similar way.