What Do Warm Edge Spacer Bars Do in Double Glazing?
Warm edge spacer bars are one of the smallest components inside a double-glazed window, but they can have an important effect on its thermal performance. Positioned around the perimeter of the sealed glass unit, the spacer separates the panes and helps create the insulated cavity between them.
Modern warm edge technology is designed to reduce heat transfer around the edge of the glass compared with traditional highly conductive metal spacers.
If you look closely between the panes of a double-glazed window, you may be able to see a thin strip running around the edge. That is the spacer bar.
It may not receive the same attention as Low-E glass, argon gas or the window frame, but it forms an important part of the complete glazing specification.
Glass Tec manufactures and supplies double glazed units from Bradford, making spacer technology particularly relevant when understanding how a modern insulating glass unit is put together.
What Are Warm Edge Spacer Bars?
Warm edge spacer bars are strips positioned between panes of glass within an insulating glass unit, often shortened to IGU.
Their basic job is to maintain the correct distance between the panes while forming part of the sealed perimeter of the unit.
Traditional double glazing often used aluminium spacer bars.
Aluminium is strong and practical, but it is also a good conductor of heat. This means heat can transfer more readily through the edge of the glazing.
Modern warm edge technology uses materials with lower thermal conductivity.
Specialist spacer manufacturer Edgetech explains that warm edge spacers are designed to interrupt this thermal bridge and reduce heat transfer around the perimeter of an insulating glass unit. Read Edgetech’s explanation of warm edge spacer technology
That is where the term warm edge comes from.
The technology is intended to keep the internal edge of the glass warmer than it would typically be with a highly conductive traditional metal spacer.
Where Are Spacer Bars Located in Double Glazing?
Look at the edge of a double-glazed unit.
You have:
- an outer pane of glass;
- an insulating cavity;
- an inner pane of glass;
- a spacer running around the perimeter.
The spacer sits between the two panes rather than being attached to the visible uPVC frame.
In other words, warm edge spacer bars are part of the sealed glass unit itself.
The spacer also helps maintain the cavity in which insulating gas such as argon may be used depending on the glazing specification.
Glass Tec offers different types of double and triple glazed units, including Low-E, argon-filled, patterned and other specialist glazing configurations.
The spacer is therefore one part of a much larger glazing system.
How Do Warm Edge Spacer Bars Reduce Heat Loss?
Heat naturally moves from warmer areas towards colder areas.
During winter, the inside of your home will normally be warmer than the outside.
The window is therefore designed to slow the movement of heat through the glass, glazing cavity and frame.
The edge of the glass matters because this is where the two panes and surrounding components meet.
Traditional aluminium spacers conduct heat relatively easily.
Warm edge spacer bars instead use lower-conductivity materials designed to reduce thermal bridging at this point.
Edgetech describes this as interrupting the thermal bridge that would otherwise allow more heat to move between the warm inner pane and colder outer pane.
The spacer does not work alone.
Overall window performance can also depend on:
- glass coatings;
- cavity width;
- insulating gas;
- number of panes;
- frame design;
- weather seals;
- installation;
- spacer technology.
That is why it is better to assess a complete window specification rather than judging performance from one component.
Why Does the Edge of the Glass Matter?
The centre of a modern insulating glass unit can perform differently from its perimeter.
At the perimeter, the glass connects with the spacer and edge-sealing system.
If a highly conductive material creates a thermal bridge, more heat can travel through that area.
The Glass and Glazing Federation’s technical guidance notes that conduction around the edge of an insulating glass unit can be reduced by using thermally efficient warm edge spacers.
This means warm edge spacer bars help tackle one of the weaker areas of an insulated glazing unit.
It is a fairly hidden component, but that does not make it unimportant.
Can Warm Edge Spacer Bars Help With Condensation?
They can help reduce the risk of condensation forming around the internal edge of the glazing.
Condensation occurs when moist air meets a sufficiently cold surface.
You may have noticed condensation appearing first around the lower edges or corners of an older window.
Because warm edge spacer bars are designed to reduce heat transfer around the glass perimeter, the internal edge can remain warmer.
A warmer internal surface can reduce the likelihood of that surface reaching the dew point under the same indoor conditions.
Edgetech identifies improved condensation resistance as one of the benefits of warm edge technology. See the warm edge spacer benefits explained by Edgetech
However, spacer bars cannot prevent every form of condensation.
Indoor humidity, ventilation, heating, outdoor temperature and other parts of the building can all affect condensation.
What If Condensation Is Between the Glass Panes?
That is a different issue.
Moisture trapped between the panes of a sealed unit can indicate that the sealed unit has failed and moisture is entering the cavity.
A warm edge spacer should not be treated as a solution for an already failed glass unit.
In some situations, the glass unit can be replaced without replacing an otherwise serviceable frame.
Warm Edge Spacer Bars vs Aluminium Spacer Bars
The main difference is thermal conductivity.
Traditional aluminium is a highly conductive metal.
Warm edge systems use materials specifically selected to transfer less heat.
| Feature | Traditional Aluminium Spacer | Warm Edge Spacer |
|---|---|---|
| Separates glass panes | Yes | Yes |
| Used around IGU perimeter | Yes | Yes |
| Highly conductive material | Yes | Generally no |
| Designed to reduce edge thermal bridging | Limited | Yes |
| Used in modern energy-efficient glazing | Can be | Commonly |
The purpose of warm edge spacer bars is therefore not simply to hold the glass apart.
They perform the spacing function while also improving the thermal characteristics around the edge of the unit.
Are All Warm Edge Spacer Bars the Same?
No.
Warm edge is a category of spacer technology rather than one single product.
There are flexible and rigid systems made from different materials and using different manufacturing methods.
Edgetech, for example, currently produces several warm edge systems including Super Spacer, Duralite and rigid thermoplastic options. View examples of modern warm edge spacer systems
The exact product used in a window should therefore be confirmed with the manufacturer or installer where it matters to your specification.
[GLASS TEC INPUT NEEDED: If Glass Tec wants to name the exact spacer brand currently used in its standard double-glazed units, confirm the current production specification before publishing that claim.]
This avoids promising a particular component where manufacturing specifications may vary.
What Else Is Inside a Double-Glazed Unit?
A double-glazed unit is more complex than two pieces of glass stuck together.
A typical modern specification can potentially contain:
- two panes of glass;
- a sealed cavity;
- a spacer bar;
- edge seals;
- desiccant;
- insulating gas where specified;
- Low-E glass where specified.
Glass Tec’s double-glazed unit range includes Low-E and argon-filled options as well as specialist decorative and solar-control glazing.
The final specification depends on what the window needs to achieve.
For example, a homeowner may prioritise:
- thermal efficiency;
- privacy;
- solar control;
- security;
- noise reduction;
- decorative appearance.
This is why warm edge spacer bars should be considered as part of the entire glass unit rather than as a standalone upgrade.
Do Warm Edge Spacer Bars Improve a Window’s U-Value?
They can contribute to improved thermal performance.
A U-value measures the rate of heat transfer through a building element. Generally, a lower U-value indicates less heat transfer.
Because the spacer sits around the perimeter of the glazing, reducing thermal bridging in this area can contribute to the performance of the complete window.
Edgetech states that warm edge technology can contribute to a lower overall window U-value by reducing heat loss at the glass edge.
However, you should not judge a window’s U-value from the spacer alone.
The final figure depends on the full system.
That includes both the glazing and frame.
If energy efficiency is your main concern, compare the specification of the complete double glazed window rather than simply asking whether it contains a warm edge spacer.
Are Warm Edge Spacer Bars Used in Triple Glazing?
Yes, warm edge technology can also be used in triple-glazed units.
A triple-glazed unit contains three panes and two cavities, so spacer components are required between the panes.
Glass Tec’s existing trade triple-glazing information describes units using two warm edge bars as part of its triple-glazing construction.
The Glass and Glazing Federation also discusses warm edge spacer bars in its technical guidance for triple glazing.
If you are deciding between double and triple glazing, however, spacer technology is only one consideration.
You can explore Glass Tec’s triple glazed windows to compare the wider glazing option.
Can You See Warm Edge Spacer Bars?
Usually, yes.
Stand close to a double-glazed window and look towards the perimeter of the glass.
You should be able to see a narrow strip running between the panes.
Depending on the product, spacer bars may be available in different finishes or colours.
From a normal viewing distance, though, they are generally a subtle part of the window.
For most homeowners, their thermal role matters more than their appearance.
Why Are Warm Edge Spacer Bars Useful in Bradford Homes?
The basic physics is the same whether the property is in Bradford, Leeds or elsewhere in the UK.
However, homeowners in Bradford frequently experience cool, wet weather for parts of the year, meaning thermal comfort and efficient glazing can be important when replacing older windows.
That does not mean a spacer bar alone will transform an inefficient property.
It is one component within an energy-efficient window.
For Bradford homeowners replacing old glazing, it makes more sense to consider:
- the condition of the current frame;
- glass specification;
- Low-E coating;
- spacer technology;
- gas filling where applicable;
- draught sealing;
- installation quality.
Glass Tec is a Bradford-based manufacturer of double and triple glazed windows and also manufactures sealed glazing units.
That manufacturing connection makes the components inside the glazing just as relevant as the visible frame around it.
Should I Ask About the Spacer Bar When Buying Windows?
It is worth asking.
Most homeowners understandably focus on window style, frame colour, glass and price.
But if thermal efficiency matters to you, asking about the complete glazing specification can help you understand what you are actually buying.
Useful questions include:
- What type of spacer bar is used?
- Does the unit contain Low-E glass?
- Is the cavity gas-filled?
- What is the complete window’s thermal performance?
- Is the specification double or triple glazed?
- Who manufactures the sealed glass unit?
- What guarantee applies to the glazing?
A good quotation should make it possible to understand the product rather than relying entirely on vague terms such as “energy efficient”.
Frequently Asked Questions About Warm Edge Spacer Bars
What Are Warm Edge Spacer Bars Made From?
There is no single material used for every product.
Modern spacer systems can use structural foam, thermoplastic and composite materials with lower thermal conductivity than conventional aluminium.
Different manufacturers use different designs.
Are Warm Edge Spacer Bars Better Than Aluminium?
For reducing heat transfer around the perimeter of an insulating glass unit, warm edge technology is specifically designed to improve on the thermal limitations of highly conductive aluminium spacers.
That is why it is widely used in modern energy-efficient glazing.
Do Warm Edge Spacer Bars Stop Condensation?
They can help reduce the risk of condensation at the edge of the internal pane by helping maintain a warmer edge temperature.
They cannot guarantee that condensation will never occur because indoor humidity, ventilation and temperature also matter.
Are Warm Edge Spacer Bars Used in Double Glazing?
Yes.
Warm edge spacer bars are widely used in modern insulating glass units to separate the panes while reducing heat transfer around their perimeter.
Are They Used in Triple Glazing?
Yes.
Triple-glazed units require spacers between their three panes, and warm edge technology can be incorporated into these units.
Can I Replace Just the Spacer Bar in an Existing Window?
A spacer forms part of the sealed insulating glass unit.
It is not normally treated as a separate homeowner-replaceable component.
If a sealed unit has failed, the appropriate solution may involve replacing the complete glass unit rather than opening it and swapping an individual spacer.
Warm Edge Spacer Bars: Small Component, Important Job
Warm edge spacer bars are easy to overlook because most of the component is hidden inside the glass unit.
Their job, however, is important.
They maintain the space between panes while helping reduce thermal bridging around one of the most vulnerable areas of insulating glazing: the glass edge.
Used alongside suitable glass, Low-E coatings, insulating cavities, quality frames and correct installation, warm edge technology can contribute to an efficient modern window.
If you are replacing glazing, it is therefore worth looking beyond the number of panes.
Ask what is actually inside the unit.
Glass Tec manufactures sealed glass units and windows in Bradford for homeowners and trade customers across the region.
For more information, explore Glass Tec’s double glazed units or contact Glass Tec Windows to discuss your glazing requirements.
