How Does Energy Efficient Double Glazing Work?

Double glazed windows have two sheets of glass with a gap in between, usually about 16mm, to create an insulating barrier that keeps heat in. This is sometimes filled with gas. Triple glazed windows have three sheets of glass, but aren’t always better than double glazed windows. To choose the most energy efficient window, look for the BFRC rating.

What are windows made from?

Energy efficient windows come in a range of frame materials and styles. Performance criteria vary according to how well they stop heat from passing through, how much sunlight travels through the glass and how little air can leak in or out around the window.

Glass

The most energy efficient type for double glazing is low emissivity (Low-E) glass. This often has an invisible coating of metal oxide, normally on one of the internal panes. This lets in light and heat but cuts the amount of heat that can get out.

Gaps between the glass

Very efficient windows might use gases such as argon, xenon or krypton in the gap between the sheets of glass.

Pane spacers

These are set around the inside edges to keep the two panes of glass apart. For maximum efficiency, look for pane spacers containing little or no metal – often known as ‘warm edge’ spacers.

Frame materials

For all frame materials there are windows available in all energy ratings.

• uPVC frames last a long time and may be recycled.
• Wooden frames can have a lower environmental impact, but require maintenance. They are often used in conservation areas where the original windows had timber frames.
• Aluminium or steel frames are slim and long-lasting, and may be recycled.
• Composite frames have an inner timber frame covered with aluminium or plastic. This reduces the need for maintenance and keeps the frame weatherproof.