The public interest registry for energy double glazing.
Frequently asked questions on energy efficient windows
Energy efficient windows come in a range of styles and designs. There are particular features you should look out for to increase energy efficiency.
How do I know which windows are energy efficient?
You can check the energy efficiency of a window by looking at the BFRC, Certass or BSI label, which is also known as a 'rainbow label'. The higher the energy rating, the more energy efficient it is. Unfortunately, at the moment there is no obligation for window manufacturers to label their products, however by opting for a high rated window you know you will be buying the most efficient.
How many layers of glass do I need?
Double glazing has two layers of glass with a gap of around 20mm between them. There's also the option of triple glazing, which has three layers of glass. Both A rated double and tripled-glazed windows are available.
What type of glass is best?
The most energy efficient glass for double glazing is low emissivity (Low-E) glass. This often has an unnoticeable coating of metal oxide, normally on one of the internal panes - next to the gap. It lets sunlight and heat in but cuts the amount of heat that can get out again.
What's between the panes of glass?
Very efficient windows might use gases like argon, xenon or krypton in the gap between the 2 sheets of glass.
What keep the panes of glass apart?
All double glazed windows have pane spacers set around the inside edges, to keep the two panes of glass apart. For a more efficient window, look for pane spacers containing little or no metal - often known as 'warm edge' spacers.
The BFRC window energy rating scheme, one of a number of national schemes used for rating the energy efficiency of windows, checks all the components to ensure the final window achieves the energy efficient standard claimed. This means that you just need to look for the A-G ratings and remember A is best. Alternatively, just look for the Energy Saving Trust Recommended logo which will only be found on glazing that is B rated or above.
Which frame suits my home?
The frame you choose will depend on your home and your personal taste. For all frame materials there are windows available in each energy rating.
- PVCu frames are the most common type. They last a long time and can be recycled.
- Wooden frames are natural, but require maintenance. They are often used in conservation areas where the original windows were timber framed.
- Aluminium or steel frames are slim and long-lasting. They can be recycled.
- Composite frames are made from more than one material. This reduces the need for maintenance and keeps the frame weatherproof
Do I need ventilation?
Because replacement windows will be more airtight than the original single glazed frames, condensation can build up in your house due to the reduced ventilation.
If there is not a sufficient level of background ventilation in the room some replacement windows will have trickle vents incorporated into the frame that let in a small amount of controlled ventilation.
Condensation can sometimes occur on the outside of new low-e glazing. This is because low-e glass reflects heat back into the home and as a result the outside pane remains cool and condensation can build up in cold weather - this isn't a problem.
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