Curtains and blinds

Well-installed curtains and blinds can help to reduce heat loss through your windows. “Sealing” the curtain or blind so that air movement between the window and the room is stopped is much more important than the material it is made from. Having your curtains and blinds open during the day and closing them just before it gets dark means your house can gain heat during the day from the sun, and better retain heat overnight. In summer, they can also help keep your home cool if you close your curtains and blinds on the side facing the sun and open the windows.

How curtains and blinds reduce heat loss

The aim is to create a good seal between the curtain or blind and the window, so that cold air from the window doesn’t get into the room, and warm air stays in the room. In cold weather, the air close to the window cools down and gets heavier. Without a good seal, it will simply fall out at the bottom of the curtain or blind, and warm room air will continuously replace it at the top. Curtains that are installed so they create a good seal can reduce heat loss through windows by up to 60% for single glazed windows, and up to 40% to 50% for double glazing. As they only work when they’re drawn, curtains are not a substitute for double glazing.

Checklist for curtains

To provide good insulation your curtains should:

  • be floor-length and touch the floor, or have pelmets above them with only a minimal air-gap between the top of the curtain and the pelmet (sill-length curtains are ineffective)
  • fit tightly against the wall or window frame
  • be wider than the window frame
  • preferably be double layered with a thick lining.

Net-curtains installed very close to the window, and in contact with the window frame, can be effective, too.

Checklist for blinds

To provide good insulation, your blinds should:

  • have a snug fit with the window frame so that they create a good seal to trap the air in the gap between them and the window (if there are gaps around the blinds then their thermal effect will be minimal).
  • specifically designed thermal blinds (sometimes described as ‘honeycomb’ or ‘cellular’ blinds) may provide additional insulation, but only if they can be installed without any gaps around them – which is hard to achieve in practice.