There are a number of options when it comes to choosing the glass in your double glazed units – from plain to patterned, coloured, stained and a number of ‘speciality’ glasses. Your choice will depend on your house style, your budget, your taste and the position of the window.
Low E Glass
Low-e glass stands for low emissivity glass. This glass varies from normal clear glass in that one side of the glass has a special metal coating, technically known as a low emissivity, or Low-e coating. Low-e glass is a type of insulating glass, which increases the energy efficiency of windows by reducing the transfer of heat or cold through glass. That means in the winter your house stays warmer, and in the summer it stays cooler.
There are two types of Low-e (low emissivity) glass available – Pyrolytic (hard coat) is considered to be a medium performer, and sputtered (vacuum deposition or soft coat) is considered to be the highest performer.
Pilkington K Glass™ (A brand of Low-e glass)
The most common is Pilkington K Glass™ which has high light transmission and appears virtually the same as clear float glass. It is the microscopic coating that makes the big difference to its performance. Glass in a window absorbs heat then radiates it again on the colder, outside, surface. Pilkington K’s low emissivity coating on the surface that faces into the air gap of the double glazing unit provides a poor radiator. The heat absorbed by the coated glass is inhibited from radiating across the air gap and then from the outer pane to the cold outside world. Instead the heat is reflected back into the room by the coating.
It works in a similar way to a sheet of reflecting foil placed behind a central heating radiator which bounces the heat back into the room. Heat losses through different materials can be compared by their U values. The higher the U value, the greater the heat loss through the material.
The U value of a single pane window is 5.6. Double glazing with ordinary glass has a U value of 2.8. Double glazing with Pilkington K Glass™ has a U value of only 1.9, considerably better than conventional double glazing, and as good as triple glazing. Because Pilkington K Glass™ is so neutral in appearance, it is recommended that its presence in a double glazing unit is confirmed on installation. This can be achieved by the use of a coating detector which unit manufacturers or installers should have available.
What took them so long? Pilkington Activ™ is the holy grail of glass. Its active coating, chemically bonded onto its outside surface, is designed to absorb the ultraviolet light given off by the sun. This absorption process causes a reaction on the surface of the glass, which breaks down and loosens dirt. Then, when it rains, the coating causes rain water to ‘sheet’ off the surface of the glass, which not only washes away the loosened particles of dirt, but also prevents the formulation of droplets, which cause streaks and make windows look dirty.
SGG PLANITHERM (A Soft Coat Low-e Glass)
This is a clear float glass, which has been coated with metallic oxides by magnetically enhanced cathodic sputtering under vacuum conditions.
This sputtered coating is highly reflective to longwave heat radiation, otherwise known as a “low emissivity” or low-e coating. This greatly reduces heat loss and ensures that double glazed units incorporating SGG PLANITHERM provide excellent thermal insulation. SGG PLANITHERM is neutral inappearance and has a high light transmittance factor.
Neutral Appearance has these main benefits:
- No unsightly tint – Unlike traditional Low-e coatings that suffer from an unsightly yellow tint, SGG PLANITHERM looks very clear. This means your curtains or Georgian Bars will not look dirty or discoloured
- More light – less tint also means more light can enter the room, making it more comfortable and luminous
- No ‘haze’ effect – SGG PLANITHERM does not suffer from the unsightly tint commonly associated with traditional Low-e products
SGG PLANITHERM is a slightly more difficult product to locate than say the Pilkington Products, so you may have to ask your supplier to specially source it for you, if having a neutral appearance is very important to you.
There are a number of options when it comes to choosing the glass in your double glazed units.