10 Important Questions to Ask Before Buying Windows
Windows, no matter their type, are something we choose only a few times in a lifetime. That’s why it’s essential to be well-informed before making a purchase and to know exactly what we expect from our windows.
Windows, no matter their type, are something we choose only a few times in a lifetime. That’s why it’s essential to be well-informed before making a purchase and to know exactly what we expect from our windows. This short guide will not only help you choose the right windows but also highlight key aspects to consider when speaking with a sales representative or manufacturer. Let’s get started.
1. Material Base – Window Profile
The foundation of windows and doors is a profile made of wood, plastic, or aluminum. For plastic windows, the construction depth and thermal transmittance coefficient of the frame (Uf) are more important than the number of chambers in the profile. A minimum construction depth of 70 mm and sealing in at least two planes are recommended. Additionally, plastic profiles should be classified according to STN EN 12608, especially in terms of their resistance to solar radiation.
2. Choosing the Right Supplier
The selection of a window supplier is crucial. It’s important to differentiate between:
- The profile system processor (e.g., a Slovak window manufacturer).
- The profile system manufacturer (e.g., plastic profile manufacturers from Germany, Belgium, or the UK).
Windows made from the same profile by different processors may vary in quality.
It’s advisable to choose established companies with proven references. Small, unknown manufacturers may offer lower prices, but there is a high risk that warranty service will be unavailable after the first winter.
3. Glazing
Insulating glass units (IGUs) are one of the most critical components affecting a window’s performance. Consider factors like:
- Thermal transmittance (Ug)
- Solar factor (g)
- Sound insulation index (Rw)
IGUs with warm-edge spacers (e.g., TGI, Swisspacer, or Swisspacer V) are preferred, as they minimize heat loss. Always ensure that the glass manufacturer has CE certification.
4. Perimeter Hardware
The hardware system plays a key role in ventilation and security. High-quality hardware should:
- Provide tight closure around the entire window perimeter (max distance between locking points: 800 mm).
Include safety features such as mishandling locks, mushroom cam locks, and security strikers.
5. Building Physics – Thermal Efficiency, Acoustics, and Light Transmission
- Double glazing transmits 11% more light and 26% more solar energy compared to triple glazing.
- Triple glazing reduces heat loss by 45% compared to double glazing.
Ensure the supplier can verify the thermal efficiency of their windows according to STN 73 0540-2.
6. Structural Integrity and Safety
Windows must comply with European safety standards (STN EN 1991-1-4/NA) to withstand wind loads and structural stress, particularly in high-rise buildings or windy areas.
7. Product Labeling
Every window must have a CE mark as per STN EN 14351-1+A1/2011. A trustworthy manufacturer also provides:
- Production date or batch number for future spare parts.
Energy labels detailing the window’s energy efficiency.
8. Contract Terms
A written contract should outline:
- Thermal transmittance values (for the entire window, not just the glass or profile).
- Warranty details and installation instructions.
Waste disposal conditions (old window removal should be handled ecologically).
9. Warranty and Service
A minimum 60-month warranty should be provided for both:
- The windows themselves.
- Their installation.
The supplier should also guarantee access to replacement parts, such as gaskets, even after their physical lifespan ends.
10. Installation and Mounting
The supplier must ensure that installation is performed by qualified professionals in accordance with STN 73 3134.
Look for manufacturers certified with a “mounting passport”, proving their expertise in proper installation techniques.