Window Replacement Grants 2026 in Luxembourg: Ug Conditions and Klimabonus Amounts

Introduction: The New Klimabonus Wunnen 2026 Program

The law of 24 July 2026 renews the Klimabonus Wunnen program in Luxembourg until the end of 2030, with effect from 1 January 2026. This scheme aims to encourage homeowners to carry out energy renovation works, including the replacement of window frames and glazing. In this article, we detail the eligibility conditions, grant amounts, and technical criteria for windows, which concern the Ug value of the glass rather than the Uw. Whether you own a single-family house or an apartment, understanding these aids can save you thousands of euros.

What is Klimabonus Wunnen 2026?

The Klimabonus Wunnen is the new financial aid system for energy renovation of homes in Luxembourg. It includes several types of subsidies: insulation, heating, renewable energy, and of course, window replacement. The 2026 law extends it until the end of 2030. The application for prior approval must be submitted before the works start.

The program's goals are clear: reduce the energy consumption of buildings, achieve carbon neutrality by 2050, and improve residents' comfort. For windows, the focus is on a very low Ug value for the glass, ensuring excellent thermal insulation.

Eligibility Conditions for the Window Frame Grant

To benefit from the window frame grant under Klimabonus Wunnen 2026, several conditions must be met:

• The home must be located in Luxembourg, in a building more than 10 years old since its building permit was issued.
• For a project limited to the windows, the works must be carried out by a company approved under the law of 21 April 1993 or benefit from spot supervision of the works by an energy adviser.
• The replaced windows must be in contact with the outside or with an unheated space (garage, cellar, etc.).
• The Ug value (thermal transmittance of the glass) must be less than or equal to 0.6 W/m²K, confirmed by the manufacturer or installer; the law sets no Uw for the complete window.
• The replacement must in principle be carried out together with external wall insulation or the installation of controlled mechanical ventilation, unless the external wall already has a U-value of 0.85 W/m²K or less.
• The application must be submitted before the start of works.

There is no income condition: the grant is accessible to all homeowners, whether owner-occupiers or landlords.

Grant Amounts for Window Frames in 2026

The grant amount is calculated on the surface area of the replaced windows, measured on their outside dimensions. Here are the main amounts:

The grant cannot exceed 60% of the costs excluding VAT (article 3 of the law of 24 July 2026). The law sets no fixed amount per home and per year, and photovoltaic panels fall under a separate scheme with their own amounts (in 2026, the amended law of 23 December 2016).

For a typical example: a house with 10 standard-size windows (about 1.5 m² each) represents a total surface of 15 m². The grant would be 15 x 70 = 1,050 EUR. If you have 20 m² of windows, the grant reaches 1,400 EUR. At the 80 EUR/m² rate, these amounts become 1,200 EUR and 1,600 EUR.

The Ug Value: The Legal Technical Criterion

The Uw value is the thermal transmittance coefficient of the complete window (frame + glazing), while the Ug value concerns the glass alone. The lower they are, the better the insulation. To qualify for the grant, the law of 24 July 2026 does not look at the Uw: it requires glass with a Ug value less than or equal to 0.6 W/m²K, which usually means high-performance triple glazing.

To achieve such performance, it is recommended to opt for:

• Triple glazing with a Ug value ≤ 0.6 W/m²K (the legal threshold).
• Frames with thermal break (wood, PVC, aluminum with insulating spacers).
• A low linear transmittance coefficient (Psi) at the frame-glazing junction.

Qualified craftsmen can help you choose certified products. Remember to ask for a technical data sheet with the guaranteed Ug value of the glass (a confirmation from the manufacturer or installer is required for the grant) and the Uw value of the window.

How to Apply for the Grant?

The prior approval application is submitted with the official form described on Guichet.lu. Here are the steps to follow:

1. Create an account on the portal (or use your LuxTrust identifier).
2. Fill in the application form indicating the type of work (window frame replacement).
3. Attach the supporting documents: quote from the company, house plan, photos, etc.
4. Wait for validation of your file (prior approval).
5. Once the works are completed, send the paid invoices to receive the grant.

It is important to note that the application must be made before the start of works. If you start works without prior approval, you risk losing the grant.

Other Complementary Aids: Reduced VAT and Insulation Subsidies

In addition to the window frame grant, you can benefit from the reduced VAT of 3% on renovation works, provided the home is meeting the age requirement. This represents a substantial saving, as the normal rate is 17%.

If you take advantage of window replacement to improve the insulation of your roof or walls, know that Klimabonus also offers grants:

• Roof insulation: a rate per square metre insulated, from 35 to 115 EUR/m2 depending on the insulant and the performance standard reached (up to 140 EUR with the transitional increase) (minimum 20 cm of insulation at a conductivity of 0.035 W/mK).
• Wall insulation: a rate per square metre insulated, from 35 to 115 EUR/m2 depending on the insulant and the performance standard reached (up to 140 EUR with the transitional increase).
• Installation of photovoltaic panels (self-consumption, at least 2 kWp): the grant follows a formula based on the peak power, i.e. 8,250 EUR for 10 kWp, and becomes a flat 10,000 EUR from 15 kWp. It cannot exceed the invoiced cost including VAT, and you must give up the regulated feed-in tariff.
• Home battery linked to a photovoltaic system (at least 2 kWh usable capacity): up to 2,250 EUR, a flat amount reached from 9 kWh usable.

By combining these aids, you can finance a significant part of your energy renovation project.

Common Mistakes to Avoid and Practical Tips

To maximize your chances of getting the grant, avoid these frequent errors:

• Not checking the Ug value of the glass before purchase.
• Starting the works before having submitted the prior approval application.
• Forgetting to provide all supporting documents (quotes, invoices, photos).
• Not keeping the original invoices.

It is advisable to consult an energy advisor to assist you in your project. This professional can help you choose the right windows, prepare your file, and optimize the aids.

Conclusion

The Klimabonus Wunnen 2026 program offers an interesting opportunity to replace your window frames at a lower cost. With a grant of 70 EUR/m² and clear technical conditions (Ug ≤ 0.6 W/m²K for the glass), you can improve the comfort of your home while reducing your energy bill. Remember to apply before starting the works and to be accompanied by qualified professionals. For more information, consult the official sources mentioned below.