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Energy Efficient Glass

Today more than ever, consumers are conscious of the need to conserve energy around the home.

Energy costs are at an all-time high and will continue to increase in the future, making new technologies such as Low-E energy efficient glass more and more attractive to budget-conscious homeowners.


Soft coat low-E glass needs careful handling

Preparing a low-E double glazing unit for installation

For many years, double glazing has been one of the most cost-effective way to reduce domestic heating costs.

Originally invented more than eighty years ago, these double-paned window units now feature in the majority of new housing.

Today, even greater savings are possible, thanks to a new generation of products. Efficient low emissivity (low-E) double glazing glass improves on conventional double glazing units by retaining more heat and absorbing the heat of the sun into the home more effectively.

The result is a significant increase in the efficiency of your home.


What is energy efficient glass?

Energy efficient glass, often called Low-E glass, looks exactly like the ordinary kind, but it has been treated with a clear metallic coating.

The coating is usually a thin layer of metal applied to the outward-facing side of the innermost window pane.

While ordinary windows allow heat to escape freely, Low-E ones trap the heat indoors by reflecting it back into the room and allows the sun to transmit heat and light into the room.


How is Low-E Glass manufactured?

There are two different types of Low-E glass: Soft Coat (sputtered) and Hard Coat (pyrolytic).

Hard coat Low-E glass is made by the CVD (Chemical Vapour Deposition) process, where it’s is coated with a thin layer of tin whilst it is still molten. This creates a hard-wearing layer which is much more durable than the soft coat type. Pilkington K is an example of Hard Coat Low-E Glass. (Pilkington do have a soft coat product called Optitherm SN, but their most widely used product is Pilkington K).

Soft coat Low-E glass is made by the MSVD (Magnetron Sputtering Vacuum Deposition) process inside a vacuum chamber, where atoms of silver, tin or zinc are “sputtered” onto the surface. This creates a very delicate layer which is easily scratched, so can only be used on the inside surfaces of a double glazing unit and must be handled very carefully when the units are being constructed.

Also, Argon gas is usually used to fill the cavity in this type of double glazing, as the soft coat can easily oxidise in an air-filled cavity.


Do all energy efficient glass types offer similar energy savings?

There is some variation in the amount of energy conservation home owners will enjoy with efficient glass.

These variations will be based on the quality of the coating, the type of gas that is sealed between the double panes of the unit, and the quality of the frame that encases the unit.

Soft coat low E glass achieves lower U values than hard coat low-E glass. However, the fragility of the soft coat means it is more difficult to handle and make into double glazing units, so the extra efficiency comes at a cost.

Once the glass has been coated, it must be used straight away (within a month or so) to be put into double glazing units. This means that manufacturers must be careful not to soft coat too much glass when they are constructing double glazing units.

It has been said that hard coated Low-E glass can have a slight champagne tint – whilst this doesn’t affect the efficiency of the glass, it can make net curtains look dirty!

Other factors such as using Argon gas instead of air to fill the space between the two panes of glass will also improve the energy efficiency of the unit considerably.

Likewise, using spacers made of warm edge technology materials (foam, acrylic, and a multi-layer vapour barrier) will result in better heat retention than spacers made of aluminium, which are a cheaper option, but a less effective barrier.


New ratings system helps homeowners select energy efficient glass products

Picture of house with double glazing next to energy rating chart

Low-E glass will help ensure your double glazing meets the highest BFRC energy ratings

The British Fenestration Rating Council (BFRC) has developed a national system for rating energy efficient windows in the UK. The rating levels range from A (for the highest level of energy savings) to E (the least efficient option).

The Energy Saving Trust, an organisation that helps UK residents use energy more efficiently, recommends choosing windows that are rated a “B” or higher.

The BFRC ratings measure a range of efficiencies, including:

  • The U value of the window (the amount of heat that can escape through the window)
  • The heat loss due to air penetration
  • The solar heat that the window lets through
  • The amount of energy that is lost through the window

These ratings apply to the overall effectiveness of the entire window unit: glass, gas-filled gap, and frame. The assembled product will be rated and labelled clearly for the consumer.


How much money can home owners save with energy efficient glass?

A household that switches from ordinary double glazing to energy efficient double glazing can see significant savings in terms of reduced energy consumption and lower energy costs year over year.

The amount of savings will depend on the type of home, number of windows, and type of windows selected. However, by using the Energy Saving Calculator provided by Pilkington, a leading energy efficient glass manufacturer, homeowners can get a general sense of the savings they can enjoy when they make the switch.

For instance, the owner of a semi-detached home requiring approximately 15 m. of glazing will see savings of almost £5,000 over a period of 20 years by switching from regular double glazing to A-grade energy efficient glass. The same household could see savings of £7,200 if they switched from single-paned glass to energy efficient double glazing.

With a sharp increase in energy prices predicted in the future, these projected savings could increase even more significantly.

Just as impressive are the environmental benefits: the use of Low-E glass will prevent nearly 10 tonnes of CO2 from reaching the environment during this time.

As energy costs continue to rise, it’s important for home owners to be aware of the new technologies that support better energy conservation.

Today’s efficient Low-E double glazing glass offers home owners an opportunity to leverage new technologies to improve heat retention and reduce energy costs in their homes.

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