We take a look at window and door glass insulating options to help you make the best choice.
The importance of reducing heat flows through windows and doors can not be overlooked. There are two main problems. Firstly, heat is lost by direct radiation. Secondly, warm air is rapidly cooled against the glass, falling to the floor to be replaced by more warm air. This is called a convective current and it can literally suck heat out of a room as fast as you can add it. For example, if you have ducted heating, the outlets are often directly under or above the windows.
Raise your glass
One of the most effective methods is by installing double or triple glazing, where sheets of glass are separated by a small, sealed airspace. Triple glazing is not commended to use in relatively moderate climate as the added cost can take considerable time to pay back in energy savings. So most insulated windows are only double glazed. Triple glazing is more common in Europe where they have very cold winters.
You can have two methods, with double or triple glazing that is made using low-e glass(this glass allows visible light to pass through into the house, while preventing heat ( infrared) from escaping) or another type of insulating glass. This will give greater heat transfer reduction, but is also more expensive.
Glass types
There are a great many variations, including tinted or toned glass, which absorb some of the light passing through the glass, thus reducing the heat ingress in summer. There is reflective glass, which reflects some of the incoming heat back in the direction it came from. This type of glass works best in summer on unshaded windows. Some types of glass are spectrally selective- they will allow visible light to pass through while reflecting UV and infrared wavelengths.
Low-e glass is ideal for cooler climates where heat loss in winter needs to be reduced. However, low-e glass can also be used in hot climates provided it is shaded from direct sun- or if it is integrated into double glazing with an outer toned pane. This is known as ‘cool glass’ in the US.
Frames
You might prefer aluminium frames which is the most popular type of frame and want them to behave in a more civilised manner. This can be achieved by introducing a thermal break inside the frame. A type of ‘ improved aluminium frames’ - basically aluminium frames with timber covering the inside of the frame- efficiently create a thermal break and make them look like timber windows on the inside.
A few technical terms
There are two values commonly used to describe the insulating properties of materials. The fist is the R-value. This describes the material’s resistance to heat transfer. An international R-rating of 1 is equivalent to a US rating of 5.71.
The second is the U-value. This measures how easily heat is transferred through the material, the opposite(or inverse) of the R-value. A material with an R-value of, say, 2.4, will have a U-value of 1/2.4=0.42. So, with R-values, the higher the number, the better the insulating properties, but with U-values, the lower the number, the better.
Reducing the pane of costs
If the panes of glass are not too big, thinner glass can be used, saving money and weight. Doors have to be glazed with safety glass and windows set down low that are larger than a certain size have to be safety glass.
Weather seals
Windows with moving sections should have good seals between the moving frame and the window frame. Most modern windows have a reasonable seal but their effectiveness depends on how well the window is designed and manufactured. The amount of air that passes through an area of window under a given pressure is known as the infiltration rating - the lower the value, the better
Another thing to remember is the installation itself. When the window frame is fitted, it must be sealed to prevent any air leaks. It is not uncommon to see windows with considerable gaps and sometimes you can feel air currents between the frame and the wall.
Well worth it
Double glazing can be expensive although it may be as little as I% of the total cost of building and can reduce energy loss through windows by 40% or more, so it is a very worthwhile investment. It is important that you get quotes from suppliers, and talk to them about what is right for your home. Remember, what applies in colder climates doesn't necessarily apply in warmer climates.
