How Energy Efficient Are Your Windows?

The spiralling cost of living, environmental sustainability, and a need to reduce carbon emissions and help manage climate change are familiar issues these days. A common thread connecting them all is energy efficiency.

Did you know that up to 20% of your home’s heat can be lost through your windows and doors?[i] This means if your home doesn’t have energy efficient windows and doors, your heating will have to work harder to keep it warm. As well as increasing your energy bills, this also increases the size of your carbon footprint. Not good for your pocket or the planet!

So, what exactly makes windows and doors energy efficient? Basically, they form a system that reduces the amount of heat lost to the outside in cold weather and prevents excessive indoor temperatures in hot conditions. We say a ‘system’ because your windows and doors are made up of different parts that each contribute towards the overall thermal performance.

First let’s consider the frame. At Liniar we produce the profiles used to make your window and door frames from extruded uPVC. This material is a natural insulator and so one of the most energy efficient to use. It’s also recyclable, and waste material generated during manufacturing is always re-used, meaning sustainability is a consideration from the very beginning of a Liniar product’s life cycle.

Then there’s the design. Liniar frames have multiple chambers inside, which trap air (another great insulator) and act as barriers making it harder for the heat inside your home to escape. You can see what this looks like in this cross-section illustration of Liniar’s EnergyPlus system. The red colour denotes the heated air from your home, and the purple shows cold air coming from outside, with a range of colours in between as the air is warmed or cooled.

Next there’s the glazing, which also plays a huge part in energy efficiency. Double glazing remains the most popular choice, although triple glazing is becoming increasingly popular in the UK and there is even the option to have quadruple glazing if the frames are deep enough. Double, triple, or quadruple refers to how many individual glass panes are used back-to-back within the same glazed unit (you may hear the term ‘DGU’ meaning double glazed unit).

There are ways to make glazed units perform better too, enhancing the overall efficiency of your windows and doors. One is to fill the space between the panes with a gas, often argon or krypton. This not only improves insulation and stops heat getting out, but also reduces the amount of noise coming in. Another enhancement is an invisible coating that reflects heat back into your home. Look out for terms like ‘low emissivity’ or ‘low-e’ glass.

Finally, the space between each set of glass panes (whether double, triple or quadruple) is sealed by a continuous strip of material called a spacer bar. This does what it says on the tin and creates space. But choosing different materials for the spacer also impacts the overall energy performance of the window or door. Although traditionally made from aluminium, metal spacer bars are highly conductive and so facilitate heat loss. For this reason, Liniar’s sister company Edgetech developed the Super Spacer, a silicone foam technology that prevents both heat transfer and condensation.

Now you know a bit more about the main window components and how they work together to deliver an energy efficient window or door by keeping more heat in your home. The friendly people at the BFRC (British Fenestration Ratings Council) have created a banding system that gives windows an energy rating from E (the least efficient) to A++ (the most efficient). They use some clever calculations that consider…

  • U-Value (of the glass Ug & the frame Uf)
  • the solar heat gain or ‘G Value’ (of the glass)
  • air leakage rate of all the components of the fitted window.

Put simply, investing in the closest rating to A++ that you can, will result in the biggest savings on fuel bills. A home fully fitted out with A++ rated windows and doors will be more energy efficient and have a lower carbon footprint, therefore being a more environmentally friendly building.

Sustainable construction methods are becoming increasingly mainstream, for example, there is growing adoption of the Passivhaus standard (a set of eco-friendly, performance-based design criteria). To find out more about Liniar’s Passivhaus certified system, visit



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