In this article, the reader will learn about double glazed windows and low-emissivity (low-E) coatings, including their components, structure, benefits, and integration. Furthermore, the article also explains the different types and application methods of low-E coatings, their positioning within double glazing, as well as their contribution to enhancing energy efficiency in homes and buildings. By the end, the reader will understand how these windows can reduce heat transfer, save on energy consumption and costs, and lower their environmental impact. Finally, the article shares tips on selecting the correct low-E coating based on individual needs and climatic conditions, and best practices for installation and maintenance.

The Use of Low-Emissivity Coatings to Further Improve the Energy Efficiency of Double Glazed Windows


Table of Contents

Understanding Double Glazed Windows

Double glazed windows have gained popularity in recent years due to their energy efficiency and effectiveness in maintaining comfortable indoor temperatures. As the name suggests, double glazed windows consist of two separate glass panes, separated by a gap filled with air or gas. These windows create a barrier that reduces heat transfer, decreases sound transmission, and minimizes the likelihood of condensation. In this article, we will delve into the components and structure of double glazed windows, as well as their benefits in terms of energy efficiency.

Components and Structure of Double Glazed Windows

Beneath the surface, the composition of a double glazed window seems quite intricate. The principal components include the following:

  1. Spacer bars and seals: The two glass panes are held apart by spacer bars, which provide structural integrity and create the gap needed for insulation. Spacer bars are typically made of aluminum, but can also be made from other materials like stainless steel or plastic. The spacer bars contain a desiccant that absorbs any residual moisture, preventing condensation within the window unit. Moreover, the gap between the panes is sealed effectively with high-quality seals to maintain gas or air filling and keep the moisture out.
  2. Gas fillings: The gap between the glass panes can be filled with air or an insulating gas, such as argon, krypton, or xenon. These gases, especially argon, are commonly used because of their superior insulating properties when compared to air. The gas filling helps reduce heat transfer through conduction and convection between the interior and exterior environments.

Energy Efficiency and the Benefits of Double Glazing

Installing double glazed windows has several advantages, particularly when it comes to energy efficiency and comfort. These benefits include:

  1. Thermal insulation and reduced heat loss: Double glazed windows provide enhanced insulation, thanks to the gas-filled gap between the two glass panes. In winter, they minimize heat loss from the interior of your home, helping to maintain a comfortable temperature without the need for excessive heating. During summer, double glazing prevents heat from entering your home, reducing the strain on your air conditioning system. As a result, you save on energy bills due to reduced energy consumption for heating and cooling.
  2. Noise insulation and increased security: The dual-pane structure of double glazed windows also acts as a sound barrier, making it more difficult for exterior noise to penetrate your home. This is particularly advantageous in noisy urban environments or for homes situated near airports or busy roads. Additionally, double glazed windows offer improved security, as they are more challenging to break compared to single-pane windows. Most double glazed units are constructed with strong locking mechanisms for added safety.
  3. Reduced condensation: Condensation on windows can lead to various issues, including the growth of mold, mildew, and an overall decline in indoor air quality. Double glazed windows help reduce condensation by maintaining a warmer surface temperature on the interior pane, thus decreasing the likelihood of moisture build-up. This results in a healthier living environment.

In conclusion, double glazed windows provide a plethora of benefits that contribute to a more comfortable, energy-efficient, and secure home. As a homeowner, investing in double glazing is an environmentally friendly and cost-effective decision that results in energy savings and improved living conditions.

Low-Emissivity Coatings: The Basics

Definition and Function of Low-E Coatings

Low-emissivity (Low-E) coatings are thin, transparent layers applied to the surface of glass or other materials to reduce the amount of radiant heat transfer. This property of Low-E coatings helps to enhance the insulating properties of windows, doors, and other building components. By reflecting a significant portion of the infrared part of the electromagnetic spectrum, Low-E coatings limit the transfer of heat through the glass surface, effectively minimizing heat loss or gain. This results in reduced energy consumption for heating or cooling and improved comfort for occupants of a building.

Not only does a Low-E coating reduce heat transfer, but it also helps to prevent the harmful effects of ultraviolet (UV) radiation on furniture, fabrics, artwork, and other objects inside a building. By reflecting or absorbing a significant portion of the UV spectrum, Low-E coatings can protect these items from fading and deterioration.

A primary function of Low-E coatings is to improve the energy efficiency of windows and doors by reducing the amount of heat that can escape through the glass in cold climates and the amount of heat that can enter through the glass in warm climates. In winter, Low-E coated glass helps retain the warmth inside a building by reflecting it back into the room, while in the summer, it reduces solar heat gain by limiting the passage of heat from the exterior to the interior. This leads to a more consistent indoor temperature, improving comfort for occupants while lowering heating and cooling costs for the building.

Types of Low-E Coatings

There are two main types of Low-E coatings: passive Low-E coatings and solar control Low-E coatings. Each type has a specific purpose and performs differently depending on the climate, architectural design, and energy efficiency objectives of a building.

Passive Low-E Coatings

Passive Low-E coatings, also known as hard-coat Low-E coatings, are designed to limit heat transfer from the interior to the exterior of a building in colder climates. These coatings consist of thin metal oxide layers deposited directly onto the glass surface. Passive Low-E coatings have relatively high emissivity values, meaning they allow more radiant heat to be emitted from the glass surface, which reduces heat loss during the colder months.

The primary advantage of passive Low-E coatings is their durability and resistance to physical damage or degradation. They can be exposed to the elements without the need for additional protection layers, making them suitable for single-glazed windows. However, passive Low-E coatings are not as effective at reducing heat gain in warmer climates or limiting heat loss in extremely cold climates.

Solar Control Low-E Coatings

Solar control Low-E coatings, or soft-coat Low-E coatings, are more advanced than passive coatings and are designed for both cold and warm climates. These coatings have lower emissivity values, meaning they emit less radiant heat than passive Low-E coatings. This results in improved performance in limiting heat gain during the warmer months and minimizing heat loss during colder months.

Soft-coat Low-E coatings are made by depositing multiple layers of metallic or metal oxide materials onto the glass surface in a vacuum chamber using a process called sputter coating. This method allows for the creation of ultra-thin, highly reflective coatings that can be customized for optimal performance in various climates and applications. The most advanced solar control Low-E coatings can reflect up to 80% of thermal energy while allowing visible light to pass through.

While solar control Low-E coatings offer superior performance in terms of energy efficiency, they are less durable than passive Low-E coatings and require additional protection to prevent oxidation or other environmental damage. Soft-coat Low-E coatings are typically applied to the inner surfaces of double- or triple-pane windows, with an inert gas filling (usually argon or krypton) between the panes to further enhance insulation.

In summary, Low-E coatings, whether passive or solar control, play a crucial role in improving the overall energy efficiency of buildings. These coatings significantly reduce heat loss or heat gain by reflecting radiant heat back into the building envelope, ensuring occupants enjoy increased comfort while the building consumes less energy for heating and cooling.Low-emissivity (Low-E) coatings are an essential component in modern double glazed windows, which play a vital role in improving thermal efficiency and reducing energy consumption in buildings. These coatings are ultra-thin metallic layers that are applied to the inner surface of the glass to minimize heat transfer, allowing the room to retain heat during winter and keep heat out during summer.

Integration of Low-E Coatings in Double Glazed Windows

Application Methods

There are two primary methods of applying Low-E coatings to the glass surface, characterized by the methods’ longevity, durability, and overall performance. These methods are known as pyrolytic deposition and magnetron sputtering.

Pyrolytic Deposition (Hard Coat)

Pyrolytic deposition, also known as the hard coat method, entails depositing a thin layer of metal oxide (typically tin oxide) onto the glass surface during the float glass manufacturing process. The coating is applied when the glass is still hot (approximately 1200°F), resulting in a strong, chemically bonded layer.

This method results in a durable, hard coat that can be easily handled and fabricated without the need for additional protection or special handling. Furthermore, the hard coat is highly resistant to scratching, allowing it to be used in single-glazed applications without fear of damage.

However, the hard coat’s emissivity is not as low as that of soft coat windows, resulting in slightly less energy efficiency. Pyrolytic deposition is also limited in the type of glass it can be applied to, as it requires high temperatures during the manufacturing process.

Magnetron Sputtering (Soft Coat)

Magnetron sputtering, often referred to as the soft coat method, involves depositing multiple layers of various materials (such as silver, metal oxides, and nitrides) onto the glass surface in a vacuum chamber. This method enables the creation of extremely thin, high-quality coatings, achieving lower emissivity compared to hard coat windows.

Despite its superior performance, soft coat Low-E windows present challenges. The thin and delicate nature of the coating requires special handling during fabrication and installation, as it is prone to scratching and damage. Additionally, the soft coat must be enclosed within double or triple glazing to protect it from the external environment, as it cannot withstand direct contact with the atmosphere.

Positioning of Low-E Coatings within Double Glazing

The positioning of Low-E coatings within a double glazed unit is crucial in determining its effectiveness and overall performance. Generally, the coating is applied to one of the internal surfaces of the glass panes (facing the gap between the panes) to minimize heat transfer through the window. The most common positions for low-E coatings in double glazed units are Surface 2 (the inner surface of the outer pane) and Surface 3 (the outer surface of the inner pane).

Positioning the Low-E coating on Surface 2 creates a barrier that prevents solar heat gain from entering the building during hot summer months, resulting in reduced cooling costs. Conversely, placing the Low-E coating on Surface 3 allows some solar heat to penetrate the glass while trapping heat inside the building during winter, helping to reduce heating costs.

The specific requirements of a building, its location, and the desired performance of the windows will dictate the most appropriate positioning of the Low-E coating in a double glazed unit. To reap the maximum benefits, it is essential to consult with industry experts and architects who can accurately assess the best solution for each project and optimize energy efficiency.

Enhancing Energy Efficiency with Low-E Coated Double Glazed Windows

Double-glazed windows have become an essential feature of modern buildings for their notable benefits in energy efficiency and indoor comfort. By employing Low-E (low-emissivity) coating technology, these windows gain an enhanced ability to minimize heat transfer and improve insulation, which in turn leads to increased energy savings, cost benefits, and a reduced environmental impact.

Reduced Heat Transfer and Improved Insulation

Low-E coated double glazed windows offer superior insulation as they help limit the flow of heat through the glazing system. Their effectiveness lies in the Low-E coating’s ability to reflect radiative heat, reduce heat loss in winter, and maintain cooler interiors in summer.

Reflecting radiative heat

The Low-E coating is a thin, invisible layer of metal oxide or silver applied to the surface of the glass, which acts to reflect radiative heat back to its source. This means that during the winter months, the heat generated inside your home is reflected back into the interior space, keeping it warmer. Conversely, in the summer months, the heat from the sun is reflected back outside, preventing overheating of indoor spaces.

Reducing heat loss in winter

In cold weather conditions, Low-E coated double glazed windows work to minimize heat loss from the building. The space between the two glass panes is filled with an insulating gas, such as argon or krypton, which further reduces the rate of heat transfer. This notably reduces the need for heating systems to work harder, resulting in lower energy consumption and improved thermal comfort.

Maintaining cooler interiors in summer

When the warmer months arrive, Low-E coated double glazed windows protect your home from excessive heat gain. The coating reflects solar radiation, preventing the interior spaces from overheating. This feature is especially beneficial in regions with hot climates, as it reduces the reliance on energy-intensive air conditioning systems to maintain comfortable indoor temperatures.

Increased Energy Savings and Cost Benefits

Implementing Low-E coated double glazed windows in a building’s design leads to a variety of energy-related and financial advantages, such as reduced energy consumption and lower heating and cooling expenses.

Reduced energy consumption

By significantly decreasing heat transfer levels, Low-E coated double glazed windows allow for reduced dependence on heating and cooling systems, leading to lower energy consumption. This translates not only to financial savings for building occupants but also contributes to more sustainable buildings by reducing energy waste.

Lower heating and cooling expenses

With improved insulation and reduced rates of heat transfer, Low-E coated double glazed windows minimize the need for constant temperature adjustments via heating or cooling systems. This can lead to significant savings in energy bills for homeowners and businesses alike.

Environmental Impact and Carbon Footprint Reduction

The utilization of Low-E coated double glazed windows also contributes positively to global environmental challenges, as they help to minimize greenhouse gas emissions and support the development of sustainable architecture.

Less greenhouse gas emissions

By reducing the energy consumption required to maintain comfortable indoor temperatures, Low-E coated double glazed windows contribute to lower greenhouse gas emissions. This supports global efforts to combat climate change and reduce the carbon footprint of buildings.

Contribution to sustainable architecture

As modern architecture continues to focus on sustainable designs and energy efficiency, Low-E coated double glazed windows are an essential feature. They cater to both the comfort of occupants and the global objective of reducing energy consumption and waste. Their implementation in residential and commercial buildings plays an important role in promoting green architecture and meeting environmental sustainability goals.

Selecting and Installing Low-E Coated Double Glazed Windows

Choosing the Right Low-E Coating for Your Needs

Low-E (low-emissivity) coatings on double-glazed windows are designed to lower the amount of heat transfer through the glass, resulting in reduced heating and cooling costs and increased comfort within the building. These coatings significantly reduce the amount of ultraviolet and infrared light passing through the glass, without compromising the amount of visible light that enters. When selecting the appropriate low-E coating for your windows, there are several key factors to consider.

Climatic Considerations:

  • Climate plays a crucial role in determining the ideal low-E coating for your windows. In colder climates, a low-E coating with a higher solar heat gain coefficient (SHGC) would be ideal, as it retains heat within the building. On the other hand, a low-E coating with a lower SHGC is more suitable for hotter climates, as it minimizes heat transfer into the building, keeping the interiors cooler.
  • In addition to SHGC, windows’ U-value is another essential factor to consider. U-value measures the effectiveness of a window’s insulation. Lower U-values indicate better insulation and higher energy efficiency. In colder climates, a lower U-value is preferred, while in warmer climates, a higher value may be more appropriate.

Orientation and Building Design:

  • The orientation of a building is vital in deciding the ideal low-E coating for windows. North-facing windows benefit from high SHGC coatings that allow for energy absorption in colder months. South-facing windows should ideally have lower SHGC coatings to avoid excessive heat gain during warmer months.
  • Building design and architecture also influence low-E coating choices. Passive solar design and energy-efficient architecture practices should be considered when selecting the right low-E windows. Architects can customize design elements such as window size, placement, and the specification of suitable low-E coatings to maximize energy efficiency and overall building performance.

Installation Tips and Best Practices

Professional Installation and Warranties:

  • Proper installation of your low-E coated double-glazed windows is essential to ensure their optimal performance and durability. It is crucial to hire experienced professionals to carry out the installation, as improper installation can result in infiltration, condensation, and reduced energy efficiency.
  • When selecting an installation company, check whether they provide warranties for their products and services. A reputable company should offer comprehensive warranties that cover both the window material and installation work. This assurance ensures that any defects or potential issues can be addressed without additional expenses.

Maintenance and Cleaning Considerations:

  • Although low-E coatings are generally durable, it is essential to maintain and clean the windows to extend their life and maintain optimal performance. Cleaning should be done with a mild soap solution and a soft cloth or sponge. Avoid using abrasive cleaning materials or chemicals that may damage the low-E coating.
  • Inspect the sealants and weather-stripping around the windows regularly to ensure their efficiency and durability. Replace damaged or worn sealants as needed to avoid air infiltration and maintain the windows’ energy-saving properties.
  • In specific projects where windows may be subjected to scratches or other potential damages, a protective film can be applied to the exterior surface of the glass. This film provides an added layer of protection for the low-E coating and can easily be removed and replaced if damaged.

In summary, selecting the right low-E coating and ensuring proper installation are crucial factors in maximizing the benefits of low-E coated double-glazed windows. Consider elements such as climate, building design and orientation, professional installation, and proper maintenance to ensure optimal performance and energy efficiency for your home or building project.

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FAQs on The Use of Low-Emissivity Coatings to Further Improve the Energy Efficiency of Double Glazed Windows

1. What are low-emissivity coatings, and how do they work?

Low-emissivity coatings, or low-E coatings, consist of thin layers of metal or metallic oxide applied to window glass. These coatings minimize heat transfer by reflecting thermal radiation, enhancing the insulating properties of double glazed windows, and thus improving energy efficiency in buildings (Saint-Gobain, n.d.).

2. How do low-emissivity coatings improve the energy efficiency of double glazed windows?

By reflecting thermal radiation, low-E coatings regulate heat transfer between the interior and exterior of a building. In colder months, the coating helps retain more heat indoors, reducing heating costs. Conversely, it limits heat gain during hot seasons, lessening the reliance on air conditioning systems and lowering energy consumption (Pilkington, n.d.).

3. How are low-emissivity coatings applied to double glazed windows?

During the manufacturing process, low-E coatings are typically applied to one of the inner surfaces of the glass panes comprising the double glazed window unit. The coating process involves depositing thin layers of metal or metallic oxide materials onto the glass using specific deposition techniques like sputter coating or pyrolytic coating (Guardian Glass, n.d.).

4. How do low-emissivity coatings affect the appearance and properties of double glazed windows?

Although low-E coatings slightly alter the window’s visual characteristics, the change is usually negligible. High-quality low-E coatings maintain a clear appearance and high light transmission, while still effectively managing heat transfer and providing thermal insulation. Additionally, they offer benefits like reduced UV radiation and glare protection (AGC Glass North America, n.d.).

5. Are low-emissivity coatings suitable for all climates and building types?

Yes, low-E coatings can be tailored to suit various climates and building types. Manufacturers offer a range of options, including coatings optimized for colder climates, which emphasize heat retention, and versions designed for hot regions, focusing on solar heat rejection. Consequently, low-emissivity coatings can be customized to address the specific energy efficiency needs of any building (Pilkington, n.d.).

6. Does the utilization of low-emissivity coatings in double glazed windows affect their maintenance and durability?

Low-E coatings do not significantly impact the durability or maintenance requirements of double glazed windows. Since the coating is applied to an inner surface of the window, it remains protected from damage caused by external factors. Furthermore, cleaning and other maintenance practices are usually consistent with standard double glazed window maintenance (Saint-Gobain, n.d.).

AGC Glass North America. (n.d.). Benefits of Low-E Glass. Retrieved from

Guardian Glass. (n.d.). Low-E Glass Technology. Retrieved from

Pilkington. (n.d.). Pilkington Energy-efficient Glazing Range. Retrieved from

Saint-Gobain. (n.d.). Low Emissivity Glass. Retrieved from


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