The information in this article is provided by EPC Belfast who supply Energy Performance Certificates in Belfast, Northern Ireland. They are specialists in window efficiency and all things related to domestic energy efficiency.
In the modern world, in which we are conscious of saving energy and becoming more energy efficient, windows in walls and doors generally consist of energy efficient glazing (EEG). EEG is the term describing glazing comprising of two or more panes of glass making up a unit which is completely sealed. These sealed glass units are fitted into the framing material keeping in with the style of the structure. Such frames are made of PVC-U, timber, aluminium, or a composite. The EEG rating is given in line with its efficiency in reducing the amount of heat and air being transferred through the window, along with the ability for sunlight to pass through into the building.
The most highly rated glazing is made with low-e glass (low-emissivity) and this is the most energy-efficient. This glass has a special property whereby one pane has been coated on its inner surface and this allows light to travel through but at the same time allows heat to go back into the room.
Energy rating and u-values
The British Fenestration Rating Council (BFRC) have created a rating system allowing window manufacturers to label their windows with its energy efficiency. This is in the form of a rating from A++ to C, where A++ is the most efficient. A u-value for the window is also calculated. This gives a value to the ease at which heat can pass through the unit. The higher the u-value, the more easily heat can pass through the window and the less energy efficient it is. Manufacturers aim for a low u-value and a label as close to A++ as possible. Home energy efficiency assessors in Belfast do not take in to consideration the u values of the windows. The generally use the thickness of the window as a metric of their efficiency.
The sealed unit. What is inside?
The glass panes in a double or triple glazed unit are filled with gas or air. If not air, the gas is an inert gas such as argon, krypton or xenon. These gases have a low conductivity and this helps to reduce heat loss. The gas will also interfere with sound waves from inside or outside the house reducing noise pollution.
The window or door frames do not have an impact on the energy efficiency and do not affect the Energy Performance of the building. However, they tend to be made of materials which are recyclable and reusable wherever possible.
The main options are:
- PVC-U: this has a longevity of about 20 years and can be recycled.
- Wood: often used in properties made of more traditional materials, wood is environmentally friendly and can be re-used.
- Aluminium: this makes slim frames which look good and are highly desirable. It is a low-impact manufacturing material and can be recycled.
- Composite: these are made of a mixture of wood, aluminium and/or plastic.
If you are based in Belfast, Northern Ireland, and need to have more details about the impact of windows in your energy performance rating of your home, you can contact a local Domestic Energy Assessor.