Learning the glass energy language can assist you with achieving energy-saving results quickly. Here's a guide to get you started.
What are the parts of a window or door called?
Windows and doors are made up of a frame, sash (windows) and panels (doors). You can download the AGWA Guide to Window and Door Terminology that shows each of these and the parts that go into them.
Window and Door Terminology (pdf)
What is a muntin?
A muntin is used in colonial windows to divide glass into multiple panes in the sash. In Australia most muntins are not part of the structure of the window but are simply glued in place.
What is a light?
Lights are individual panes of glass within a window.
What is an insulated glass unit?
This term applies to two (double glazing), three (triple glazing) or more panes of glass that are separated and sealed by insulation at the edges. There is air between the panes. They provide greater thermal efficiency to a window.
A double-glazed unit or IGU is comprised of two panes of glass separated by a cavity containing air (or another gas) and hermetically sealed. An IGU provides thermal insulation and improved acoustic performance. An IGU is described in terms of the thickness of the outer pane in millimetres, followed by the gap width between the panes and finally the thickness of the internal pane (for example: 4/12/4). The greater the gap width (towards about 20 mm), the better the insulation performance. The inclusion of an inert gas such as argon instead of air and the specification of low-E glass further improves the insulation provided by the IGU.
What is gas filled glass?
An inert gas, usually argon, is used between the panes of glass in an insulated glass unit instead of air. Gas is a better insulator than air so it increases the thermal efficiency of the window.
What is toned or tinted glass?
This is glass that has been coloured during manufacture by the inclusion of oxides. There are a number of colours that are generally available including grey, green, blue and bronze. Tinted glass will have an effect on the energy efficiency and also the amount of light that enters through a window.
What is low-E glass?
Low-E stands for low-emissivity. Glass is coated with a very thin, virtually clear material that acts to reduce the transmission of infra-red rays through the glass. Depending on the type used low-e coatings can be used to prevent heat coming in through a window in hot climates and, in cold climates can reduce the amount of long wave heat energy that is lost from a warm interior to the outside. Low-E glass improves thermal efficiency while allowing visible light through.
What is light transmittance or visible transmittance (VT)?
Visible transmittance measures how much light comes in through a product. It is an optical property that is expressed as a number between 0 and 1. The higher the number, the more light is transmitted.
How does a door keep the outside elements from penetrating into the interior?
The door works in concert with weather stripping, the door frame, and the threshold to keep the elements at bay. Usually, the door itself has insulating value provided either by its mass, as in a solid door, or by insulating material fabricated into the core by its manufacturer. The weather stripping, door frame and threshold prevent air penetration around the door.
What makes an external door different to an internal door?
An exterior door needs to be finished to resist the elements. This requires that any wood be either sealed or covered with a weather resistant material. The exterior door must be manufactured of materials that are weather resistant.
What is coated glass?
Glass may be coated 'on-line' or 'off-line' (independent of the manufacturing process). On-line coatings are called 'pyrolytic' and, because of their high durability, can be further processed (cut, toughened, curved, etcetera). Off-line coated products are often referred to as 'sputtered' coatings and some of these coatings need to be protected within a double-glazed unit or a laminate. Once manufactured, off-line coated products are generally not suitable for further processing other than cutting.
What is laminated glass?
Laminated glass panes are assembled from two sheets of glass sandwiching an interlayer, which bonds the glass (usually PVB). A heavy impact can break laminated glass, but won’t splinter it. This leads to greater safety and security. Laminated glass eliminates nearly 99% of harmful UV rays, greatly slowing the fading of floors and furniture. A specialized interlayer in laminated glass can further reduce the Solar Heat Gain Coefficient (SHGC).
What is Reflective Coating?
To create a reflective coating, a metallic coating is applied to one side of the glass in order to significantly increase the amount of reflected visible and infra red heat.
What is Solar Control Glass?
Solar control glass is glass that reduces heat gain derived from direct solar radiation. This may be achieved via interlayers, body tints, reflective coatings or Low E coatings.
What is a Solar Heat Gain Coefficient (SHGC)?
The SHGC is the ratio of solar heat admitted by the glazing into a building, compared with the energy striking the outside surface of the glazing. It includes directly-transmitted radiation plus indirect heat gain from re-radiation and convection of absorbed heat from the glass into the building. The lower the number, the less solar heat is allowed in.
What is U-Value?
The U-value indicates the rate of heat flow through a window due to a temperature difference, from inside to outside (in winter) or from outside to inside (in summer). Heat is lost and gained through a window by the combined effects of conduction, convection and radiation. The lower the number, the higher the thermal performance.
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