Double glazing

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Potential energy savings with double glazing

Different types of double glazing will provide different levels of energy savings. However B-rated double glazing can save £165 on the average annual energy bill.

What is the effective lifespan?

It varies depending on the quality of materials used, depth of cavity between inner and outer pane, temperature differences, workmanship and location of installation both in terms of facing direction and geographic location. The glazing units typically last from 10 to 25 years, with windows facing south or north often lasting less than 12 years.

What to look for

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Some manufacturers show the energy efficiency of their windows using an energy rating scheme from A to G - like the one used for appliances such as fridges. The efficiency of the whole window (the frame and the glass) is assessed and the scheme is run by the British Fenestration Rating Council (BFRC).

Other things to look for include:

  • the most energy-efficient glass for double glazing is low emissivity (Low-E) glass. This often has a coating of metal oxide that lets in light and heat but cuts the amount of heat that can escape.
  • deeper cavities between the two panes - 16mm is the optimum distance
  • the cavity being filled with an inert gas, usually argon
  • pane spacers: These are set around the inside edges and keep the two panes of glass apart. Look for pane spacers containing little or no metal, often known as ‘warm edge’ spacers.

Other advantages

Other advantages of double glazing include:

  • higher security can be achieved by installing double glazing from the inside - the units cannot be removed easily from the outside. Ask your supplier for details.
  • peace and quiet: as well as keeping the heat in, energy-efficient windows insulate your home against outside noise
  • reduced condensation: energy-efficient glazing reduces condensation build-up on the inside of windows
  • comfort: energy-efficient glazing reduces heat loss through windows, meaning fewer draughts and cold spots
  • a smaller carbon footprint: by using less fuel, you’ll generate less of the carbon dioxide that leads to global warming - typically, 680kg a year

Conservatories, and conservation areas

Even the best quality glazing loses heat more quickly than an uninsulated cavity wall, which means that conservatories are not thermally efficient and should not be heated. However, provided they are not heated and the doors to the conservatory are kept shut in cold weather, they can actually reduce heat loss by acting as an extra insulating layer outside your house. You can make the most of this by installing a sealed sliding door and sealed blinds or heavy lined curtains to separate the conservatory more effectively from the rest of your house.

Double glazing, blinds and curtains can all reduce the amount of heat wasted, but it is not possible to bring a conservatory up to the thermal standard of even an averagely insulated room. If you want to save energy and money, save your conservatory for the summer.

Finally, if you live in a conservation area or a listed building there may be restrictions on what you can do to your windows.


  • Secondary glazing: a secondary pane of glass and its frame can be fitted inside the existing window reveal. It won’t be as well sealed as a double-glazed unit, but will be much cheaper to fit and will still save energy - you could save about £100 a year on fuel bills - and low emissivity glass would improve its performance. Secondary glazing kits are available for the proficient DIYer to install themselves - they reduce costs and are a non-intrusive way of insulating your windows.
  • Curtains lined with a layer of heavy material can reduce heat loss from a room through the window at night, and cut draughts. Hollow blinds fitted into place with a sealed frame and sealed shutters will also help cut draughts and retain your heat for longer.
  • Fitting draught-proofing to the doors and windows will save the typical household around £30 a year

Page last updated 30 August 2012

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