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Which windows and doors system are the most energy efficient?

With home heating bills at an all time high and a government drive to reduce carbon emissions, we’re all looking for new ways to improve our home’s energy efficiency. One of the best ways to do this is by replacing your windows and doors. So, which windows and doors systems are the most energy efficient? Let’s take a closer look.

How do windows and doors affect energy efficiency?

Did you know that UK homes lose anywhere between 10% and 40% of heat through the windows and doors? When you want to improve your home’s thermal performance, the windows and doors are a good place to start.

When a window becomes inefficient it can lose heat through the glass itself, through the frame (also called the window profile), and through the window seals.

To find out which windows and doors are the most energy efficient, we need to look at these three elements.

What is the best glass to improve energy efficiency?

The most energy efficient type of glass is low emissivity (low-E) glass. Low-E glass features a microscopic metal oxide on one of the internal glass panes.

The metal oxide layer reflects any heat from inside the home back inside, stopping it from escaping and improving the property’s thermal performance.

Low-E glass also helps to regulate the way the sun’s rays penetrate through the window glass.

Harmful UV rays are reflected off the window and away from the property helping to reduce unwanted interior heat during the hot summer months.

Sunlight, however, is allowed to pass through the metal oxide layer. This means that the low-E glass does not have a negative impact on a room’s natural light.

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Which window profile is the most energy efficient?

When it comes to window profiles, the most energy efficient profile will be determined by the way it was constructed and the material that was used.

  • Modern uPVC profiles have been designed to maximise energy efficiency. They feature a multi-chambered design that helps the window to stop heat from escaping from inside the home
  • Timber window frames can also achieve high levels of energy efficiency. Wood has a naturally low level of thermal conductivity, which means that it is more difficult for heat to escape through a solid timber frame
  • Composite frames often combine a timber or insulating foam core with a plastic outer layer. This design is good for weather protection but does not provide as high levels of energy efficiency as timber or uPVC profiles
  • Aluminium windows are the least energy efficient. Aluminium, like all metals, is highly thermally conductive. Modern aluminium windows, however, feature polyamide thermal breaks which help to reduce heat loss by blocking the transmission of heat waves through the frames

Double vs triple glazing

Double glazing is a popular choice for homeowners across the UK. In recent years, however, triple glazing has greatly increased in popularity because of its superior insulating capacity. Both double and triple glazing work on the same principles. The space between the window panes reduces the speed that air can escape through the window.

The window gaps are often filled with an inert gas such as Argon or Krypton. This further helps to reduce heat loss and improve insulating capacity.

As triple glazing features an additional glass pane, it creates an extra space between the windowpanes. This enables the window unit to achieve higher levels of energy efficiency.

Window energy ratings

All windows manufactured in the UK are given a Window Energy Rating (WER). The WER rating scale runs from E (the lowest) to A++ (the most efficient).

WER ratings are calculated by comparing the window’s heat retention capacity with the rate at which interior heat escapes from the window.

Current building regulations state that all replacement windows and windows installed in new-build homes must achieve a WER rating of C or lower.

The importance of U-values

U-values are the most important factor for determining a window’s energy efficiency capacity. U-values measure the amount of heat lost through a window because of thermal transfer.

Heat moving from the warm side to the cold side of the window is measured over a specified time period. The type of glass, the use of spacer bars, and the type of gas in the window gap will affect the window’s U-value.

Typical U-values for uPVC double glazed windows are around 1.4 W/m²K. For triple glazed windows, U-values will likely be closer to 1.0 W/m²K or lower.

Energy efficient doors

Although more of a property’s heat is lost through the windows than the doors, it’s still important to ensure that your doors are as energy efficient as possible.

Any glass areas of an entrance door will perform in the same way as a window. For patio doors with large, glazed areas, the same considerations will be needed as for windows.

For front doors with little or no glass areas, the factors are slightly different. Effective draught proofing, high-quality seals, and professional fitting can all help to optimise a front door’s energy efficiency performance.

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What kind of windows are most energy efficient?

Fixed windows or fixed lights (windows that cannot be opened) are the most energy efficient.

In terms of openable windows, side hung, or top hung casement windows are the most energy efficient. This is because when they are closed, they form an effective weathertight seal.

What is the most energy efficient window material?

uPVC and timber are less thermally conductive making them the most energy efficient materials. Metals such as steel and aluminium are more thermally conductive and require thermal breaks to improve energy efficiency.

What is the most energy efficient front door?

This will depend on the door’s design. Timber, uPVC, and composite doors are all designed to improve thermal performance and will help to improve a home’s heat retention capacity.

What type of window is the least energy efficient?

In general aluminium windows are the least energy efficient.

Is it worth replacing your windows?

This depends on the reasons for replacement. If you want to improve the energy efficiency of your home, then yes, replacing your windows is worth it.

If you want to increase the value of your home, however, replacing your windows is not the best way to get returns on your investment.

Is it worth installing triple glazing in the UK?

Yes. Triple glazing provides significantly better levels of energy efficiency than double glazing. It is also becoming increasingly popular and is often used in new-builds to meet increasingly strict energy standards.

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