Save up to 80% energy with simple tricks

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Heating costs are rising and rising. Why? Worldwide, fuels such as oil and gas are getting more and more expensive. No one wants to come home to a cold house in the winter. That’s why methods of lowering energy consumption and saving on heating costs are in high demand. On this page we have compiled a list of FAQs related to the topic of energy efficiency. So you can stop throwing your money out the window.

What do windows and doors contribute to the thermal insulation of a house or flat?

Good thermal insulation is only as effective as the weakest chain in the link. This is often old windows and entrance doors. The best masonry is of little use if you have old doors and windows, possibly even with single glazing, in the wall. After long use window and door frames are often warped and the seals are often brittle or defective. This allows cold air to flow freely into the rooms and the warm air to escape.

Did you know that

  • new Weru windows insulate about five times better than single-glazed windows?
  • Windows installed before 1995 are considered to be energetically obsolete?
  • the German Energy Saving Ordinance (EnEV) prescribes an insulation value of 1.3 W/m²K for energy-efficient windows?

With insulated windows from Weru you can even beat the EnEV specification with standard glazing. This is also the case with new entrance doors with insulated panels and profiles. Stop throwing your money out your old windows and doors!

Photo of building taken with a thermal imaging camera
Left photo: before window replacement,
right photo: after installation of new windows

The ‘Uw value’ is often used to express energy efficiency. What does it stand for?

This value, which used to be called the ‘k-value’, is also known as the thermal transmittance and is given in watts per square metre Kelvin (W/m²K). It indicates the amount of heat that flows through 1 m² of a window at a constant temperature difference between the outside and the inside of the window of 1 Kelvin.

The thermal transmittance Uw is made up of the thermal transmittance of the frame and sash profile (Uf), the glazing (Ug) and the glazing sealant compound used.

Less is more when it comes to the U value:
the lower the Uw value, the better the window’s thermal insulation.

Rule of thumb:
For every 10% improvement in the Uw value you save about 1.2 litres of heating oil per square metre of window area per year.

Doesn’t sound like much? Let’s say you replace your windows from before 1995 (approx. Uw = 2.8 W/m²K) with new Weru insulated windows (Uw = 1.0 W/m²K). For a single-family dwelling with a window area of approx. 30 m² this amounts to approx. 650 litres less heating oil!

What are the technical possibilities for equipping windows and doors to have better thermal insulation?

The perfect interplay between all components is key. This means profile material, profile geometry with installation depth and number of chambers, insulating glass, hardware technology and seals, and in the case of entrance doors the insulated door panel. With Weru products all parts can be individually adapted to achieve even better thermal insulation values.

  • Insulating glass
    With insulating glass from Weru even the stringent requirements of the German Energy Saving Ordinance (EnEV) can easily be met [Link Lexikon]. Decisive for this result are thermal protection measures for the glazing, in the space between the panes and for the spacers. The insulating glass panes coated with wafer-thin metal foils allow the short-wavelength rays of light in, but reflect the long-wavelength heat rays from the living space back inside. Noble gas filling in the space between the panes makes an additional contribution to increasing the thermal insulation. With highly insulating triple glazing from Weru you can even reach Uw values of up to 0.68 W/m²K and thus multiply your savings potential.
  • Glazing spacer
    This keeps the thermally insulating noble gas in the space between the panes and prevents penetration of water vapour. Highly insulating PVCu glazing spacers reduce fogging up of the pane on the room side at the edges of the glazing beads.
  • Window profile (‘window frame’)
    The relationship between the number and size of the profile chambers and the installation depth of the profile must be optimal.
    The thermal insulation properties can be improved even further with a profile filled with thermally insulating foam – the ThermoPlus profile [Link wohin?].


You can further improve the thermal insulation properties of a window with the following elements:

Glazing with thermal protection

Activate your energy-saving potential with WERU windows. Depending on the design situation, we can offer you a variety of thermal protection windows with thermal insulation values of up to 0.5 W/(m²K), so that even the strict energy-saving regulations (EnEV) can be met without any problems.

Contained in:
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Condense-Stop glazing spacer

Highly insulating PVCu spacer

  • reduces condensation on the glass pane above the glazing bead
  • ensures a pleasant living climate due to a consistent surface temperature
Contained in:
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Aluminium glazing spacer

Are resistant to temperature, UV- and ageing, absorb dynamic loads and, with a linear thermal transmittance of 0.064 W/(mK), also have excellent thermal insulation properties.

  • Individually bookable

Optimises the thermal efficiency of the profile system through a clever chamber geometry paired with thermally insulating foam, reduces thermal bridging through full-perimeter foaming even in corner area of profile and ensures a feeling of well-being with consistent glass and surface temperature.

Contained in:
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  • Trend+++
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  • Door profile
    As was the case with the windows, the relationship between the number and size of profile chambers and the installation depth of the profile must be optimised.
  • Thermally insulating door panel
  • Insulating glass for doors with glass elements

What role does professional installation play in insulated windows and doors?

Reduced energy consumption, decreased CO2 emissions and correspondingly lower heating costs: Your new insulated windows can only pay off if they are professionally installed. Physical laws and sufficient stability as well as the fastening and sealing materials used play important roles in achieving this.

If, for example, the building joint isn’t sealed properly, moisture from the air can condense and accumulate in the expanding foam. With 5% moisture penetration the thermal insulation performance is lowered by 50%! If this defect remains undetected, over the long term it can lead to moisture and mould damage in the window joint. This is usually costly to repair.

Without qualified professional installation by installers who undergo regular training, you as the builder or renovator cannot be assured of the highest-quality execution according to the latest state of the art. The key prerequisite for the functionality and longevity of your new insulated window. You can rely upon professional quality for your “Thermally Insulated Window Project: Your Weru specialist dealer will properly install your insulated windows to the highest standards. This will give you the ideal basis for long-lasting reduction of your energy consumption and savings on heating costs.

Did you know that improper installation of windows and doors can eventually lead to moisture and mould damage?

What is an energy passport? When and for what is it needed?

The building energy performance certificate was introduced on 1 October 2007. It assesses a house according to the energy needed for its operation. The buyer or tenant thus receives a very good indication of how high or low the energy consumption and the corresponding heating costs will be. As the seller or landlord of a property you are obligated to present the energy performance certificate. Otherwise you may even have to pay a fine.
The energy performance certificate also contains recommendations for upgrades to improve energy efficiency. And they pay off several times over: Insulated dwellings attract tenants more quickly and can be sold at a higher price. So, stop paying unnecessary energy costs and reduce energy consumption now by installing energy-efficient windows from Weru.

Is it true that you can get money from the government for energy-efficient new builds and renovations?

The federal government and numerous state governments support the replacement of old windows and doors through special funding programmes as well as by offering cheap loans. The latest information on the numerous funding programmes can be found via our funding search tool.

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