Insulating windows correctly: thermal insulation explained in simple terms

What is window insulation?

Window thermal insulation refers to all measures and properties that help to reduce heat loss through windows, thereby saving energy, increasing living comfort and improving the indoor climate. In detail, window thermal insulation includes:

• Reduction of heat loss: Modern designs and materials effectively prevent both heat conduction through the window surfaces and frames and the penetration of draughts.

• U-value: The so-called heat transfer coefficient indicates how well a window insulates – the lower the U-value, the better the thermal insulation.

• Multiple glazing: Thermal insulation glass with special coatings minimises heat loss, while gas fillings in insulating glass further increase the insulating effect.

• Insulating frame materials: Plastic, wood or thermally separated aluminium frames with integrated insulation prevent cold bridges and improve energy efficiency.

• Seals: Multiple, precisely fitting seal levels ensure that warm air remains inside and cold air cannot penetrate from outside.

• Prevention of thermal bridges: Specially developed window constructions prevent areas where excessive heat could escape.

• Sun protection: Intelligent control of light incidence allows solar energy to be utilised in winter and prevents rooms from overheating in summer.

• Integration of innovative materials: Heat-insulating core materials or coated glass increase efficiency, while combinations of plastic, wood and aluminium optimise both insulation performance and maintenance properties.

• Sustainability: The use of recyclable materials and energy-efficient production contribute to environmental friendliness.

• Subsidies: Government programmes and grants facilitate investment in energy-efficient windows and help to meet the requirements of the Energy Saving Ordinance.

Window thermal insulation: modern windows offer these important protective functions

Thermal insulation in windows plays a key role, as it significantly influences the energy efficiency, comfort and operating costs of your home. It protects against heat, cold and draughts and helps to meet the requirements of the Energy Saving Ordinance (EnEV)

Energy and efficiency

The following focuses on aspects that reduce energy consumption and improve the long-term cost-effectiveness of a property:

• Energy savings through new windows: Old or leaky windows allow valuable heat to escape uncontrollably. This leads to higher heating requirements, rising heating costs and increased energy consumption. Modern thermal insulation windows prevent these losses and save a noticeable amount of energy.

• Indoor climate & summer comfort: Poor insulation causes draughts and cold surfaces in winter. High-quality glazing and coatings keep excessive solar heat out in summer and ensure more comfortable room temperatures.

• Climate protection: Optimised thermal insulation reduces heating requirements and CO₂ emissions, thus actively contributing to environmental protection.

• Cost-benefit ratio: Replacing or retrofitting windows can be economically worthwhile, as the investment is often cheaper than permanently high heating costs and, depending on the design and energy prices, usually pays for itself within about 8 to 15 years.

Protection and comfort

These aspects increase well-being and safety within your own four walls:

• Moisture protection & mould prevention: Inadequately insulated windows promote condensation, frost damage and mould growth. Good insulation and suitable surface temperatures significantly reduce these risks.

• Sound insulation: Optimised insulation on windows improves protection against outside noise and creates more peace and quiet indoors.

• Increased value: Thermal insulation windows increase the long-term attractiveness, market value and quality of life of a property.

• Burglary protection: Modern windows with sturdy frames and special glazing increase security against attempted break-ins.

• Flexible retrofitting: Acrylic glass secondary glazing and other systems enable cost-effective insulation measures that can be implemented without complete replacement.

• Protection against mechanical influences: High-quality window systems offer additional protection against wind pressure, heavy rainfall and other weather influences

Different approaches to window thermal insulation

To effectively improve the thermal insulation of your windows, you can take various measures that vary depending on the condition and possibilities of your home. These measures can be used individually or in combination to reduce heat loss, save heating costs and increase living comfort. For sustainable energy savings, the combination of good glazing, insulated frames, seamless sealing and insulation of adjacent components is particularly important.

• Replace seals: Replace old or brittle seals or retrofit them to prevent draughts and minimise heat loss. This is a simple, inexpensive measure with a big impact.

• Install thermal insulation glazing: Replacing or retrofitting single glazing with double or triple glazing with thermal insulation coating greatly improves the U-value. New glazing is one of the most important measures you can take.

• Apply insulating film: Special thermal insulation or insulating films that are stuck to the glass reflect heat back into the room. These can provide a quick and inexpensive improvement for older windows. However, care should be taken to avoid unwanted reflections.

• Insulate window reveals: Retrofitting insulation boards or foam to window reveals reduces thermal bridges and significantly improves overall energy efficiency.

• Insulate roller shutter boxes: Roller shutter boxes are often uninsulated and cause considerable heat loss. Insulating them with special foam or insulation inserts reduces these sources of loss.

• Optimise frame material: If windows are being replaced, you should look for thermally insulated frame materials such as plastic with multi-chamber profiles, wood or thermally separated aluminium.

• Seal windows: In addition to seals, sealing joints and gaps around the window can also prevent draughts (e.g. with sealants or sealing tapes).

• Interior windows or additional glazing: Installing a burglar-proof and heat-insulating additional window on the inside of the room improves the insulating effect without completely replacing the window.

• Use curtains and roller blinds: Closing blackout curtains or roller blinds at night provides simple thermal insulation and significantly reduces heat loss.

• Adjust windows correctly: Check that the windows close properly and adjust them if necessary to prevent leaks.

Energy Saving Ordinance and funding opportunities for window thermal insulation

The Building Energy Act (GEG), which has been in force since 2024 and replaces the previous Energy Saving Ordinance (EnEV) and other regulations, sets out the legal requirements for window thermal insulation in Germany. Key points are:

• Maximum U-value for windows: New windows must have a maximum heat transfer coefficient (U-value) of 1.3 W/m²K; for roof windows, the limit is 1.4 W/m²K. Lower U-values mean better insulation (e.g. double or triple glazing). When replacing windows, a maximum U-value of 1.1 W/m²K is required for the glazing, provided that the frame is suitable.

• Requirements for existing buildings: In the case of major modernisation or renovation work (involving a change of 10% or more to external components such as windows), the new components must at least meet the minimum energy requirements. This is intended to reduce heat loss.

• Retrofitting obligations: There are obligations to improve energy efficiency, for example when structural work is carried out on the building. Exceptions exist, for example, for owner-occupied single-family and two-family houses if they have been owned since 1 February 2002.

• Insulation requirements and limit values: In addition to windows, thermal insulation values are also prescribed for other components such as walls and roofs in order to increase overall energy efficiency. In combination with windows, these measures contribute to CO₂ reduction.

• Subsidies: The government offers various subsidy programmes for energy-efficient renovations and the replacement of old windows with energy-efficient models, mostly as part of KfW or BAFA programmes. The aim is to provide financial support for investments in efficient thermal insulation and to achieve climate targets.

Step-by-step guide: Installation and quality assurance of window thermal insulation

Would you like to improve the thermal insulation of your windows in a sustainable way and ensure that the installation and quality are right? Then follow a structured approach – from selection to final acceptance.

That's why Salamander myWindow experts are important in all these steps:

• Competent advice: They help you choose the right window product with optimum thermal insulation.

• Precise planning: They take building physics into account to determine the optimal installation location and process.

• Professional implementation: Professional installation increases the service life and efficiency of the windows.

• Quality assurance: Salamander uses modern testing methods to ensure long-lasting functionality and thermal insulation.

• You benefit from first-class support and long-term warranties.

Step 1: Planning and selecting the right windows

Choose windows with suitable thermal insulation properties, e.g. with multi-chamber profiles and modern thermal insulation glazing, such as those offered by Salamander myWindow. Salamander's experts will provide you with competent advice on which system is best suited to your building and your requirements.

Step 2: Positioning the window in the insulation layer

The 5x5 rule summarises the basic principles of correct ventilation in an easy-to-understand way: Ventilate for at least five minutes to exchange the air completely. Repeat the air exchange regularly throughout the day, at least five times a day, especially in heavily used rooms.

Step 3: Measure and prepare the opening

The window opening must be measured precisely and adjusted if necessary. The professionals at Salamander ensure that the wall opening is cut to size and prepared accurately so that the new window fits flush and is dimensionally accurate.

Step 4: Mechanical fastening of the window frames

Salamander specialist fitters use suitable fastening systems (mounting rails, brackets) that securely fix the window in place without compromising the insulation. This prevents deformation and ensures safety.

Step 5: Ensuring sealing and airtightness

High-quality sealing of the connection joint is crucial to prevent draughts and moisture. Salamander myWindow experts use durable, elastic sealants and pre-compressed sealing tapes and carefully check the airtightness in accordance with current standards.

Step 6: Thermal insulation of the joint

The installation joint is filled with thermal insulation foam or insulation boards to minimise heat transfer. Salamander specialists know exactly which materials and techniques are best to prevent thermal bridges.

Step 7: Adjustment and inspection of window function

After installation, the window sashes are precisely adjusted so that they close tightly and operate smoothly. Salamander specialist fitters check and make any necessary corrections to prevent draughts and heat loss.

Step 8: Building physics testing and quality control

Experts carry out thermography and airtightness tests (e.g. blower door test) to ensure that the installation quality meets the requirements and that there are no weak points. Salamander offers these tests and gives you peace of mind that the installation is perfect.

Step 9: Documentation and instruction

All work steps, materials used and test results are documented. In addition, you will receive instruction on the care and maintenance of your new windows – all included when you work with Salamander myWindow.

Avoid common mistakes in window insulation

Avoid these common mistakes to ensure that your window insulation works optimally and you save on heating costs:

• Replacing windows without suitable façade insulation: If the window frame is better insulated than the adjacent wall, thermal bridges are created, which increase the risk of moisture damage and mould.

• Incorrect positioning of the window: A window should not be centred in the reveal, but should be integrated into the insulation layer in front of the façade or installed flush with the exterior wall to avoid thermal bridges.

• Incomplete insulation around the window frame: Especially under the window sill, there are often hard-to-reach areas where heat can escape unhindered.

• Inadequate or incorrect sealing: Installation foam alone is not elastic enough; compressible tape should be used on the outside and airtight foil on the inside to prevent air and moisture leaks.

• Dirty installation surface: Dust, dirt or uneven areas reduce the adhesion of sealing materials and lead to leaks.

• Missing or damaged vapour barrier: Without a functioning vapour barrier, moisture can penetrate the building fabric and cause mould and structural damage.

• Incorrect installation of the window sill: A lack of slope causes water to remain standing and damage the window and façade.

• Damage to the window frame: Scratches or dents can impair the sealing effect and weaken the stability of the frame.

• Use of unsuitable sealing materials: Different materials require adapted seals in order to be fully effective.

• Thermal bridges due to incorrect installation depth or metal frames: Thermally separated profiles and the correct installation depth reduce heat loss and increase energy efficiency.

Improve window insulation with solutions and products from Salamander myWindow

For maximum energy efficiency and noticeably greater living comfort, Salamander myWindow relies on German-made quality, state-of-the-art technologies and sustainable production processes. Whether in new buildings, renovations or special architectural projects, all systems are designed to minimise heat loss, permanently reduce heating costs and at the same time ensure design diversity and durability.

Advantages and features of Salamander myWindow at a glance:

• Wide range of profile materials: plastic, aluminium, wood or material combinations – each with optimum insulation values

• Excellent insulation values: meets high efficiency standards up to certified passive house solutions

• Energy savings & comfort: reduced heat loss, lower heating costs and a pleasant indoor climate in every season

• Individual selection: recommendation by the digital myWindow C3 tool – tailored to location, building type and design preferences

• Future-proof construction: durable, sustainable and eligible technology and material

• Passive house quality: triple glazing, thermally separated profiles and optimised designs prevent thermal bridges

• Sustainable materials: recycled components and recyclable profiles for a lower carbon footprint

• Customisation: from narrow, heritage-compliant profiles to generous sliding systems for modern architecture

• Eligible for subsidies: many systems meet KfW requirements and support solar energy gains

• Multi-chamber profiles: 5- to 6-chamber systems to reduce heat loss and improve sound insulation

• Thermal separation: frame constructions to prevent thermal bridges and ensure consistent room temperatures

• evoCore technology: PET recycled foam core as a lightweight, more stable and better insulated replacement for steel reinforcements

• Coextrusion: recycled material in the profile core for stability and resource conservation

• Noticeable reduction in heating costs: less heat loss and optimised energy use

• Greater living comfort: even room temperatures without draughts

• Protection & security: effective sound insulation and increased burglary protection up to RC

• Individual design: wide range of surfaces, colours and styles

• Easy planning: support from the window configurator or the myWindow C3 app

FAQ: Frequently asked questions about window insulation

Want to know more about window insulation? Here you will find answers to the most frequently asked questions so that you can make an informed decision for your home.

What are the benefits of thermal insulation films for windows?

Thermal insulation films can retain some of the heat in the room, thereby reducing heat loss. They are an inexpensive temporary solution, especially for older windows. However, they do not improve the airtightness and do not achieve the insulation performance of modern windows with a low U-value.

What is the best heat protection for windows?

The most effective protection against heat is achieved with heat protection glass, a low U-value and external sun protection such as external blinds or awnings. This combination prevents your rooms from heating up too much in summer and at the same time ensures good insulation in winter.

What is the difference between heat protection glass and insulating glass?

Heat protection glass has a special coating that reflects heat rays and reduces heat loss. Insulating glass consists of two or more panes of glass with a gas filling that also insulates. Modern windows often combine both techniques to achieve maximum heat protection.

What is a good U-value for windows?

A U-value of 1.0 W/m²K or lower is considered energy efficient. Passive house windows achieve Values of 0.8 W/m²K or less. The lower the value, the better the window retains heat in the room and the lower your heating requirements.

How much energy can I save with new windows?

That depends on your current window type. Replacing single glazing with modern triple glazing can reduce heating costs by up to 30% and improve the indoor climate at the same time.

What role does the frame play in thermal insulation?

The frame has a significant influence on the U-value of the window. Frames made of plastic, wood or thermally separated aluminium with multi-chamber systems prevent thermal bridges and increase overall energy efficiency.

Why is professional installation so important for thermal insulation?

Even the best window loses its insulating effect if it is not installed correctly. Professional installation ensures airtight connections, prevents thermal bridges and guarantees that the specified U-value is achieved in practice.

How can I improve the thermal insulation of my existing windows?

In addition to replacing them, you can optimise existing windows by replacing the glazing, sealing joints, using secondary glazing or thermal insulation films. This reduces heat loss without having to replace the entire window

Are windows with good thermal insulation eligible for subsidies?

Yes, if the windows comply with certain U-value limits, you can receive subsidies from KfW or BAFA. This reduces the investment costs and makes replacing windows even more attractive.

Find the right thermal insulation now – with Salamander myWindow

With our energy-efficient window systems, you can combine maximum thermal insulation, sustainable materials and individual design. Start planning now with the myWindow C3 tool, use our window configurator or contact us and let our specialist partners advise you – for greater comfort, lower energy costs and a sustainable future!