Reducing heat loss through home windows

Last updated: 6 September 2022

When you consider that a single pane of glass can lose almost ten times as much heat as the same area of insulated wall, it is worth taking some simple steps to reduce heat loss through your windows to make your home more comfortable and reduce your heating costs.

Size and orientation

The size and orientation of your windows will affect the amount of sunlight entering your home. West, east and north-facing windows tend to be exposed to sunlight, while south-facing windows receive almost no direct sunlight. If you are planning a renovation consider orienting your living areas and windows to the north, and rooms where you spend less time to the south. This will take advantage of the winter sun, keeping these rooms warm, light and bright.

Heat loss from windows: Warm air moves toward cold glass; heat is lost through unprotected glass.

Frames and glazing treatments

The strength of window frames, together with the glazing component, can greatly affect the energy efficiency of windows. The most energy efficient window frames are made from materials that won't transfer heat and cold, such as timber, uPVC or combination frames.

Coverings and shading

Appropriate window protection creates an insulating layer of still air on the inside of the glass. This can be achieved by the addition of thick curtains and a pelmet. A poorly fitted curtain allows heat loss to occur, while a well fitted curtain combined with a pelmet significantly reduces heat loss, so remember to:

  • use closely woven, close fitting internal window coverings such as curtains or blinds
  • ensure a snug fit on both sides of the window and at the top of the curtain to stop warm air from moving down behind the curtain and cooling
  • install pelmets (like a scarf over the top of your curtain rod) or solid barriers above the curtain rail, or position the curtain within the window space
  • use curtain tracks that provide a return of curtain to the wall to create a seal
  • close curtains or blinds when you have the heating on, especially at night.
Poorly fitted curtains lose heat. Well fitted curtains with pelmet trap heat.


Up to 25% of winter heat loss from existing houses is caused by air leakage (also known as draughts). Seal gaps around doors and windows to draught-proof your home and save energy and money.