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How Does Double Glazing Work?

Your home’s double glazing plays a huge part in its overall energy efficiency rating. According to the Energy Saving Trust around 18% of a home’s heat is lost through its windows. As well as helping to keep warm air trapped in your home in the winter months, double-glazed windows can also help you help your home to stay cool in the searing heat of summer by sealing in conditioned and recirculated air. They are also great at helping you to maintain your privacy and solitude by blocking out unwelcome noise from outside and keeping sounds from within your home. 

Installing double glazing is a pretty amazing addition to your home. But how does it work? 

Join us as we take a look at what’s going on between those two panes of glass to show you how double-glazed windows are able to bring you the wealth of fantastic benefits that they do. We’ll also look at how double-glazed windows are made so that you can better understand their workings. The more you know about how double glazing works, the more empowered you are as a consumer to choose the best double-glazed windows for your home. 

double glazed upvc windows with view

How do double-glazed windows insulate?

Single glazed windows allow heat transfer between two separate temperature zones (i.e. inside and outside). Glass is not a terribly efficient insulator with a U-Value of 5.8. As such, around 70% of the heat generated indoors passes through the pane of glass and into the air outside your home. This is a significant amount of heat loss that can severely impact on your energy bills.

Double glazing creates a gap between the inner and outer panes of glass. This is filled with an inert gas that reduces how much heat transfers from indoors to outdoors. The two glass panes are separated by a spacer bar and sealed within a self-contained unit to prevent the gas between the panels from leaking out. When the airtight seal on these units wears, the gas can seep out, rendering windows less energy efficient. 

The extra layer of gas between the panes slows down the heat transfer because air cannot circulate within the gap and convection is inhibited. This reduces heat loss.

The same principle is why double glazing helps provide acoustic insulation too. As sound waves travel to the window, the nearest pane of glass transfers them. The gas between the layers then slows down the movement of the waves of vibrations that create sounds. As such, they are much less likely to transmit through to the other side.  

It is also possible to get triple glazing for the windows in your home. Triple glazing works in the exact same way as double glazing, but it adds another glass pane and an extra layer of insulating gas. Triple glazing improves the thermal efficiency and acoustic insulation of windows even more – however it is a lot more expensive. Unlike double glazing, where the cost is usually repaid by energy bill savings, the increased thermal insulation of triple glazing does not reduce energy bills enough to cover the costs.

To find out if double or triple glazing is the right option for you, take a look at our guide to triple glazing.

What is argon gas & what does it do?

Argon gas is the insulating gas commonly used in the air gap inside a double-glazed sealed unit. It is the substance that lends double-glazed windows much of their potency as it slows the transfer of heat between panes of glass, thereby insulating your home. Argon is by no means the only noble gas that is used to this effect in window construction. A range of others can be used including krypton, nitrogen, xenon and even oxygen. 

However, argon is largely preferred by manufacturers for a number of reasons:

  • It is highly versatile and can be used in a wide range of climates and temperatures
  • It has a 34% reduced thermal transfer rate when compared to air, offering great energy efficiency
  • Its U-value is greater than comparable gases like krypton
  • It is completely colourless, odourless and non-toxic, therefore harmless in the event of a leak

man installing new double glazed window

How are double-glazed windows made?

The manufacture of a double-glazed window is essential to its effectiveness and longevity. So, how are double-glazed window units made?

The sealed window unit (also known as an insulated glass unit or IGU) is the key to the window’s workings and is also the part most prone to failure. This is why the manufacturing process is so important. 

First, the two panes of glass are cut to size in accordance with the measurements provided by the customer and checked by our team. Spacer bars are also prepared to size, containing a crystalline desiccant inside to draw moisture from the gap.

The material of the spacer bar is very important. Older aluminium spacer bars are fairly cheap, but they are also natural temperature conductors, acting as thermal bridges that can transfer cold from outside into the home. Warm edge spacer bars, on the other hand, are made from a combination of stainless steel and polypropylene to inhibit thermal conduction and reduce heat loss at the edges of the unit.

There are two processes by which argon is added to the unit. 

The most common method is to drill two holes into the frame and pump argon into the unit. However, this may lead to a small amount of air mixing with the argon. 

An alternative method requires the first pane is glass to be laid, and the spacer bars put into position. The assembly then moves through an argon-filled chamber. While the assembly is moving, the second pane is carefully pressed on top, sealing in the argon gas. 

This process is usually automated and/or carried out in an atmosphere of pure argon to prevent other gases from entering the sealed units. 

A bitumen-based sealant is then applied, usually in a molten state to provide flexibility and ensure that the unit remains airtight. 

The double-glazed unit is then ready for assembly. It can be placed in the customer’s choice of frame material and installed in the window cavity. Some window frames have screws that join the pieces of the frame together, while others have mouldings that hold the IGU in place within its frame.

Ready to transform your home with new double-glazed windows?

Double-glazed windows can have a truly transformative effect on your home. They can help your home retain heat and maintain a clement temperature all year round. They can prevent unwelcome noises from creeping into your living space while keeping sounds from your TV, stereo or private conversations indoors where they belong. Furthermore, they can potentially make your home more secure and increase its beauty and kerb appeal. 

As we’ve discussed, however, the build quality and installation make all the difference. At Emerald, we have over 40 years of experience in manufacturing and installing double-glazed windows, doors and conservatories, making us the ideal choice to help your household enjoy all the benefits of new double glazing. 

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