Energy Efficiency Explained


Energy efficiency has become an important factor when choosing windows and doors. However, the terminology can be confusing. From U Values to Window Energy Ratings, here is our quick and easy guide to energy efficiency for windows and doors.

Energy Efficiency Image.jpgGlass

Double glazed windows consist of two sheets of glass with a gap in-between, creating an insulation barrier which keeps heat in your home. Triple glazed windows have three sheets of glass, each separated by a gap in-between.


The most energy efficient glazing is low emissivity (Low-E) glass also known as Soft Coat. This often has an invisible coating of metal oxide on one of the internal panes, letting in light and heat but cutting the amount of heat that can escape. To increase energy efficiency further, the ‘gap’ can be filled with a gas such as argon, xenon or krypton.


Set around the inside edges of the two or three panes of glass are spacer bars. For maximum efficiency, look for pane spacers containing very little or no metal, these are referred to as ‘Warm Edge Spacer Bars’.


Be aware though, that triple glazing is not always more energy efficient. The energy rating of a window or door doesn’t just depend on the glass, but on the other materials in the window and their U Values.

All of our windows come with Soft Coat (Low-E) glass, filled with Argon Gas, and Warm Edge Spacer Bars as standard.

U Values

U Values are not generally talked about in England as much as in other countries across Europe, however you will still find them mentioned in literatuEnergy Certificatere and your sales person may talk to you about them.


Quite simply, a U Value measures how quickly heat will pass through a material and, in turn, how much heat will be lost through a surface. The lower the U Value, the better insulator a material is and the less heat that will escape through it. By stopping heat escaping, energy efficiency will increase and money can be saved on heating bills.

Window Energy Ratings

Every window sold in England should have an Energy Rating Certificate. This is a rainbow label, similar to the one you would see when you buy a household appliance.


The label will tell you how energy efficient your window is, detailed on a scale from A to G. A is the most energy efficient, G the least efficient. Depending on who you buy the windows from, the Energy Rating Certificate should display the BFRC, BSI, FENSA or CERTASS logo.

We are proud that all of the windows that we offer achieve an Energy Rating of A, as standard, and an average U Value of 1.4. For more information, call us on 01325 381630 or email