What should you look for?

• Glass- The most energy efficient type for double-glazing is low emissivity (Low-E) glass. Low-E glass often has an invisible coating of metal oxide, normally on one of the internal panes- letting in heat and light but reduces the amount of heat lost.

• Gaps between glass- Gases such as argon, xenon, and krypton are used between the panes of glass and are only used in metal energy efficient glass. 

• Pane spacers- These are set around the inside edges to keep the two panes of glass apart. Look for pane spacers containing little or no mental for maximum efficiency.

   

Frame materials

• PVCu frames can be recycled and last a very long time, they also come with minimal maintenance.

• Wooden frames can have a lower environmental impact but they do require a lot of maintenance- you can often find them used in conservation areas where the original windows had timber frames.

• Aluminum and steel frames are slim and long lasting and can be recycled.

• Composite frames have an inner timber frame covered with aluminium or plastic reducing the need for maintenance and keeps the frame weather proof.

U-values

Windows that have an energy rating will have the u-value of the window displayed on the energy label.

A u-value is a measurement of how easily heat can pass through a material. Materials that let out more heat have higher u-values whereas the material that let less heat pass through them have lower u-values.

In some cases windows that have a higher energy performance rating might have a higher u-value than windows with a better energy efficiency rating- this might seem the wrong way around as lower u-values indicate better insulation levels. Though in these cases it will be that there are other aspects of the window that make them better overall such as coating etc.

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Ventilation

Replacement windows will be more airtight than your original frames, so condensation may build up in your house due to the reduced. If your house does not have much background ventilation, look for replacement windows with trickle vents incorporated into the frame to let in a controlled amount of ventilation.

If you start to see condensation building up on your windows, there may be a damp problem in your home. As a general rule, damp occurs when there is inadequate ventilation, inadequate heating, inadequate insulation or a combination of these. If you’ve started to notice condensation in between the panes of glass in your double-glazing units then it is likely that the seal is broken, and the unit will need to be replaced.

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Saving and Costs

By installing double glazing in an entirely single glazed home you could save the following each year (England, Scotland and Wales).

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Benefits of energy efficient windows:

• Reduced energy bills.
• Smaller carbon footprint
• More comfortable home: energy efficient glazing reduces heat loss through windows and means fewer draughts and cold spots.
• Peace and quiet: as well as keeping the heat in, energy efficient-windows insulate your home against external noise.
• Reduced condensation: energy efficient glazing reduces condensation build up on the inside of the windows.

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Before installing double glazing, check with your local planning office if any of the following apply:

• You live in a conservation area.
• You have an article 4 direction on your property, removing the right of permitted development.
• You live in a listed building.
• Most people have double-glazing fitted by a professional.

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