Energy efficiency in practice: the impact of windows on bills


Energy efficiency is not only a buzzword in modern ecology, but also one of the key issues for many households trying to minimise the running costs of a building. Choosing the right windows is one of the key factors affecting the energy efficiency of your home. In this article, we take a look at how windows affect our bills and what solutions will help you save energy.

Why are windows important in terms of energy efficiency?

Windows are one of the main points of heat ‘escape’ from the interior of a building, especially if they are old or inadequately sealed. Poor thermal insulation of windows can lead to heat loss, resulting in higher energy consumption for heating in winter and cooling in summer.

Window types and energy efficiency

  • Single-glazed windows – the oldest window type, characterised by the worst thermal insulation. Nowadays rarely used, but still present in many older buildings.
  • Single-glazed windows.
  • Double-glazed windows – consist of two panes of glass with a layer of air or gas (e.g. argon) between them. They provide better insulation than single-glazed windows, but are less efficient than modern triple-glazed windows.
  • Triple-glazed windows – the latest technology that provides the best thermal insulation. There is a layer of air or special gases between the panes of glass to increase their energy efficiency.

What affects the energy efficiency of a window?

The optimum energy efficiency of a window determines the comfort of the occupants, as well as the size of the heating and cooling bills. When choosing a window for your home or flat, there are several key factors to consider:

Glazing type

  • Single glazing – The least energy efficient available on the market.
  • Single glazing – The least energy efficient available on the market.
  • Double glazing – Better thermal insulation than single glazing, due to the layer of air or gas between the panes.
  • Transparent glazing.
  • Triple glazed – The most energy efficient, with three layers of glass and two air or gas spaces.

Window frames

  • PVC – Good insulating properties, easy to maintain, but may (but not necessarily – depends on manufacturer) be less environmentally friendly in the manufacturing process.
  • Wood – Natural, good insulating properties, but requires regular maintenance.
  • Aluminium – Durable, but can be less insulating than PVC or wood.


Seals ensure the tightness of windows, preventing cold air from entering in winter and keeping cool air inside in summer. Ageing seals can cause leaks, which reduces the energy efficiency of the window.

Additional technologies

  • Low-emissivity coatings – Coatings that will reflect heat energy into the room, thereby increasing energy efficiency.
  • Low-emissivity coatings – Coatings that will reflect heat energy into the room, thereby increasing energy efficiency.
  • Gas infill between the panes – Gases such as argon or krypton inserted between the panes increase the insulation of the window as they have a lower thermal conductivity than air.
  • Roller blinds and shutters – Can provide additional insulation, especially at night or during hot weather.

Shape and design

Windows with simple shapes (square, rectangular) tend to be more energy efficient than those with irregular shapes, whose shape can encourage leaks.

The design of the window, including the way it opens (e.g. tilt, turn) and the quality of the locks and hinges, can affect its airtightness.

Orientation to the world

South-facing windows can benefit from the sun’s natural heat, which is beneficial in colder climates. In warmer climates, they may need to be covered during the day to avoid excessive heat build-up.

North-facing windows tend to be cooler and less exposed to direct sunlight.

The energy efficiency of a window depends on many factors working together. It is important to take all these aspects into account when choosing a window and to adapt it to the specific characteristics of the building and the climatic conditions of the region.

How to choose energy-efficient windows?

  • Pay attention to the U-value – This is a measure of the heat conductivity of the window. The lower the U-value, the better the insulation of the window. For triple-glazed windows, this value is often below 1.0 W/m²K.
  • Check certificates and labels – Certified windows guarantee a certain level of insulation. Look for labels such as “A++” or “Passive House” for the best energy efficiency.
  • Consult with experts – It’s a good idea to consult with a professional or window installation company before making a choice. They will help you to choose the best solution adapted to the specific building and climate conditions.
  • Guarantee and service – It is a good idea to choose windows with a long-term guarantee and service assurance. This demonstrates the quality of the product and gives you confidence in future support.

What can an investment in energy efficient windows give you?

Investing in energy-efficient windows is a step towards reducing energy bills and providing thermal comfort for the occupants. It is worth paying attention not only to the price, but above all to the quality and insulating properties of the window. In the long run, the right choice of windows can bring significant savings.

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