Which energy efficient windows are best for an eco-friendly home?
You want to buy energy efficient windows, but you are not sure whether you require double glazing, secondary glazing or triple glazing, Low-E coating windows, PVCu or wooden window frames. Also how does the solar gain work?
We will now bring some clearness and clarity to the range and choices of windows.
A little information on windows…
Glazing is essential as it provides light into your home while maintaining heat, therefore lowering your energy bills while making your home warm and comfortable.
We are now going to look at glazing including the frame and the opening, this will help determine the best performance window for the price. We will also look how pergolas, integrate blinds and light shelves can be used to enhance the amount of light entering your home, then finally poor installation issues. Most of these issues apply to external doors.
Solar heat gain
When the heat of the sun raises room temperature, this is called the solar gain. This is effected by the strength of the sun (time of the year and location in the country), the angle and type of glazing which transmits or reflects this energy. Energy efficient windows are designed to maximise solar gain during the winter period, while controlling room temperature in the summer.
uPVC Windows concede heat and light differently during the year. It is maximised depending on the angle of which the sunlight hits the surface of the glass. If this is within a 20 degrees angle then most of the light will pass through it; over 35 degrees then most energy will bounce off.
Measuring solar gain
The solar energy which is transmitted through the window measured by the ‘G-value’, which range from 0 to 1 (the higher value indicates more solar gain). This is specified on the energy label of a new window.
The values are the sum of primary solar light transmittance (T-value) plus the secondary transmittance (absorption within the window and shading device).
South facing windows a G value of 0.76 or greater is recommended.
Large west facing windows should be coated with E to G value, less than 0.6 which prevents overheating.
The best energy efficient windows are ‘A’ rated!
Within the UK modern windows are rated by the British Fenestration Rating Council (BFRC). ‘A’ rating windows are the highest rating whilst ‘C’ is the minimum. According to the Energy Saving Trust, A rating have a payback within five to six year.
The best type of glazing for energy efficient windows
Triple glazing is the best type of window, if you can afford it (a lot more expensive than double glazing), it has long term energy savings, if you require an ‘A’ rating.
Other energy efficient windows have inert gas (argon, krypton or xenon) sealed with the panes. This gas minimises heat conduction from the building, far better than air does; xenon is the most effective, whilst argon is the cheapest.
The gaps between the window panes should the minimum of 16mm, however they can be less if gas filled. All seals should be perfectly fitted, no air should enter through gaps into the window, and otherwise condensation forms inside the windows.
Low-E coatings on windows
This is a special coating which reflects infrared radiation which can be applied to the inside surface of one pane. This is called the ‘low-E’ coating. During the colder periods, the low-E deflects heat back into the room, reducing heat loss and heating costs. During warmer periods, the outer-surface deflects heat out of the house, cooling the property.
Other window coatings
A self-cleaning coating can be added to the external pane, this is extremely popular and useful for a conservatory roof or skylight. This is achieved by manipulating ultraviolet light to decompose organic materials, then the rain washes them off. We can also provide a huge range of other coatings during manufacturing, e.g. to only permit 6% light into a room, or 8% heat. These extra eco-windows have extra-clear outer layers, allowing up to 80% light and 71% sun heat in. While triple glazed units would reduce this to about 65%.