Save Energy

Saving money with energy efficient windows


The windows that we select for our homes bring light, warmth, and beauty into them. Energy efficient windows, when correctly selected and installed, will help to minimize the heating and lighting costs and will also increase comfort and the amount of useable living space. Energy efficient windows will cost more initially but will not only improve comfort but also will save energy and money for the life of the window.


When purchasing new windows it is important to choose good quality products compliant with local and leading international standards. Selecting energy efficient windows has been and still is a daunting task for householders in Bulgaria due to the lack of certification and a clear and independent window rating system that allows them to rapidly compare the energy efficiency of different products. Therefore, when selecting windows for energy efficiency the following information should
be requested from the supplier/installer and should be carefully considered:

•  Air flow through the whole window (L-value, measured in m3/m2/h) – Uncontrolled air flow through a window loses heat and creates uncomfortable draughts. Windows with good quality frames and seals, installed by qualified and reputable installers, reduce uncontrolled air flow and provide good air tightness.

•  Heat transfer coefficient of the whole window (U-value, measured in W/m2.K) – An important factor for the energy efficiency of a whole window is the U-value. A window with a low U-value loses less heat than one with a high U-value, i.e. a window with a low U-value will reduce your heating costs.

Note: Always ensure that a U-value quoted by supplier or installer is for the whole window and not simply for the glass or the frame. The lower the U-value, the more energy efficient the window is.

The following factors affect the whole window U-value:

•  The type of glazing materials – Clear float glass has previously been the major material used for windows in houses. Advances in glazing technology mean that special glass is now available to control heat loss through the window. This low-emissivity (low-e) glass has special surface coatings to reflect heat back through the window. The low-e coatings reflect from 40% to 70% of the heat that is normally transmitted through clear glass. This type of glass is now standard under the Building Regulations for most homes in the EU countries.

•  The number of glazing layers and the size of the cavity between the glazing layers – The traditional approach to improving the energy efficiency of a window has been to increase the number of layers of glass and air. Double- or triple-glazed windows have insulating air- or gas-filled spaces between each pane. Each layer of glass and the air spaces resists heat flow. The width of the air spaces between the panes is important, wider air spaces have lower U-values and allow less heat transfer. Highly energy efficient windows are manufactured with inert gases (argon or krypton) in the spaces between the panes because these gases transfer less heat than air.

•  The design, material and type of frame – Window frames are available in a variety of materials and the frame material can be selected for price, maintenance or visual appearance. Any frame material can produce energy efficient windows if designed correctly. For consumers, it is important to get the most energy efficient window from the frame material that is chosen.

The requirements for the selection and replacement of windows in the home are covered by the Building Regulations. Householders are advised to contact a building regulations consultant for details of these requirements.