Are you wondering how to lower your energy bills? Choose new windows containing PLANITHERM – proven to be the most energy-efficient window glass available in the UK

Laminated Glass

PLANITHERM is a new generation of energy saving window glass that uses advanced coatings to retain more internal warmth whilst capturing free energy from natural daylight.

Using PLANITHERM, you can have A rated windows installed for around the same cost as less energy efficient windows. A staggering 26% of all domestic heat loss escapes through the windows*. Installing A rated energy efficient windows can save you up to 28% per year on your heating bills compared to traditional windows and frames.

If you are planning to replace your existing single glazed or double glazed windows, and you want the best possible choice for energy savings, ask us for PLANITHERM.

PLANITHERM products use a special coating to reflect heat from domestic heat sources back into the room, rather than allowing it to escape outside through the windows. In addition to this, the coating allows free heat and light from the sun to pass through the glass, warming the room and further contributing to the energy efficiency of the windows and helping to reduce your energy bills.

This combination of unrivalled thermal insulation with high solar heat gain makes PLANITHERM the most energy efficient window glass available and the best possible choice for energy savings.

If you install windows with PLANITHERM your home will be lighter, brighter, warmer and more energy efficient thanks to the advanced thermal insulation of PLANITHERM.

Free Solar Heat Gain – PLANITHERM has a unique coating which captures free energy from natural daylight to heat the home.

Thermal Insulation – The coating reflects heat back into the room, helping to keep the room warmer and reduce heating bills.

Optimal Energy Ratings – As PLANITHERM is the most energy-efficient glass available, A-rated windows can be achieved using energy-efficient frames.

Haze and Tint free windows – PLANITHERM maximizes natural light entering the home without the tint or haze effects associated with some other double-glazed windows.

Eliminates Condensation – PLANITHERM helps to reduce draughts and cold spots around windows and helps to virtually eliminate internal condensation.

For further information, ask us about PLANITHERM or visit

* Source: Energy Saving Trust

Capable of withstanding an attack.

Sheets of glass are bonded – or laminated – together with a layer of polymer film (PVB) in between. By using heat and pressure, air bubbles are eliminated from the laminate (in equipment called an Autoclave) so that it appears optically as a single sheet. Laminated comes in several different thicknesses and can be used as a form of security. Standard thickness is around 4.5mm, we would advise a minimum of 6.4mm for household security.


Used for areas in need of extra safety, glazed doors and glazing adjacent to doors as standard. Float glass is heated to about 650C in a furnace, then quenched with air jets so that the surfaces are cooled quickly and the inside core more slowly with the surfaces going into ‘compression’ and the core going into ‘tension’.
(Toughened Glass is NOT for security but purely for safety)



‘Low-E’ glass which usually forms the inner pane of a double glazing unit, allows less heat to escape through your windows than ordinary glass. Thanks to a special energy saving coating which lets the sun’s rays through, but reflects heat from fires and radiators back into your home. Also available as laminated, toughened and patterned.

There are several versions of ‘Low-E’ glass:

  • ‘K’Glass – made by Pilkingtons will achieve an energy rating of ‘E’ which is 1.7.
    This is the base of UK Regulations but does not meet EU regulations which is a minimum of 1.5
  • Soft Coat Glass – made by Saint Gobain and has an energy rating of 1.4 which is ‘C’ rated.

‘Low-E’ glass benefits:-

  • make your home more comfortable
  • make your home more appealing
  • help reduce your energy costs
  • reduce sun glare and noise
  • cuts heat gain and loss during warm and cool months
  • lengthens the lifespan of furnishings against fading
  • improves the security and safety of your home (if Laminated Glass is used)

Heat Efficient Windows

  • Radiant heat originating from indoors is reflected back inside, thus keeping heat inside in the winter.
  • Infrared radiation from the sun is reflected away, keeping it cooler inside in the summer.

Hard / Soft Coated Glass
Hard coated ‘Low-E’ products, such as Pilkington K, have been used predominantly in the UK. They are easier to process but have a slight champagne tint which can make white net curtains look discoloured. A better U Value can be achieved with a soft coated glass such as Saint Gobain’s Planitherm, which reduces heat loss further. The product is also much clearer with no visible tint.

Source: The Sunday Telegraph
Date: 15 July 2012
Author: Jeff Howell

Through a Glass Dimly:

Question: Last December we had La Porte French Doors installed.
According to the product specification they are “Factory Glazed with 24mm Toughened Double Glazed Units with low-e glass and Argon gas filled”. Whenever the sun shines on them the glass takes on a dull appearance and looks dirty. There is no indication of condensation at anytime. The manufacturers are coming to inspect the glass but have told us that this is normal given the current regulations covering this type of glass. Is this correct ?

Answer: Yes, that’s right. All new and replacement windows have to conform to the Building Regulations standard for thermal insulation. This means that at least one pane of a sealed unit must be low-emmissiviy (or “low-e”) glass. Low-e glass works by having a coating which reflects heat, but since heat and light are part of the electromagnetic spectrum, anything that reflects heat must also reflect light. That’s why many people notice that their homes appear to be darker following the fitting of new windows. The low-e coating can also make the glass appear hazy or dirty when the sun shines on it at an oblique angle. I’m afraid this is the price you have to pay for the thermal performance.

NOT at Weatherproof Windows, we use a softcoat glass using Planitherm, not a hard coat glass like Pilkington K.

Insulation glass without ‘Low-E’ coating uses air between the panes as a primary source of insulation. As air itself is a good insulator, filling the gap between the glass panes with a low-conductivity gas such as argon reduces conductive and convective heat transfers. This is because the density of the gas is greater than the density of the air.

Argon is the most commonly used fill gas, due to its excellent thermal performance and cost-efficiency in comparison to other gas fills. Argon gas reduces heat loss in sealed units by slowing down convection inside the air space. It is extremely cost-efficient, and works well with ‘Low-E’ coated glazing. Argon and Krypton are colourless, odourless, non-flammable and non-reactive inert gases.

Several techniques are used to fill the IG cavity and all techniques result in a mixture of fill gas and air. It is generally accepted that the IG unit should achieve a 90% fill gas concentration. Over time this concentration will gradually evaporate, at an estimated rate of 0.5 to 1% per year. IG units filled with argon do not degrade significantly until they reach 75% concentration, which means up to 20 years of durability.

A major benefit of IGU is that it is passive, so it does not require a switching-on process to work. Argon gas is a relatively inexpensive option, and quickly produces heat cost-savings that justify its cost.

Krypton is more effective at reducing heat loss, but is roughly 200 times more expensive than argon per unit volume. Because Krypton works best at smaller pane spacings (8 mm), it is often used in triple and quadruple-glazed windows to minimize the overall thickness of the unit.

Other types of gases are used (for example, sulphur hexafluoride, carbon dioxide) to reduce sound transmission, but these gases do not offer the improved thermal performance of the inert gases.

Recent innovations in glass technology have given us “Self Cleaning Glass” which has been heavily promoted as Pilkington “Activ” or Saint Gobain “Bioclean”. These are predominantly used for conservatory roofs or any areas that can be hard to reach for cleaning purposes. The chemical reaction reacts to organic substances which adhere to the glass and activates when rain falls, which helps release the dirt particles. Other glass cleaning chemicals should not be used on this type of glass for cleaning purposes.
We must point out that Self Cleaning Glass is not the same as having a window cleaner.


Did you know that almost half of all the UK’s carbon dioxide emissions come from our buildings and homes?

Windows play a huge role in this. According to the Energy Saving Trust, around 20% of the heat lost from an average home occurs through the windows. The heat lost contributes half a tonne of CO2 per home to the atmosphere and increases fuel bills.

Reduce Heat Loss Through Your Windows
Warm Edge Spacer is approximately 950 times less conductive than aluminium and, as most of the heat loss through a window occurs at the edge of the unit, standard metal spacer bars act as a thermal energy drain allowing heat to escape from your home. Warm Edge Spacer blocks the escape route.

Warm Edge Spacer, is new energy saving technology. Windows with Warm Edge Spacer reduce heat lost through your windows, helping to keep your home warm. Less heat lost also means lower fuel bills and lower carbon emissions.

Reduce Noise & Condensation
There are many other benefits of installing windows with Warm Edge Spacer. It reduces condensation by up to 65%, virtually eliminating the potential breeding ground for bacteria, mould and dust mites that can be harmful to people with respiratory diseases. Warm Edge Spacer also reduces noise transmission by up to 2dB which helps you keep your home an oasis of calm, away from the noise of the outside world.


Many Window companies will be trying to achieve high energy ratings to add to the quality of their overall product range and to offer consumers greater informed choices about the products they offer

Window profiles are part of the story but as glass makes up most of the area in a window and the components used in its construction are critical to achieving good levels of insulation.

Instead of just Centre pane U value the W.E.R is concerned with the heat loss of the whole window.

Therefore a combination of Coated Glass, Low Iron Glass, Warm Edge Technology and gas filling is critical to achieve a good rating.

Energy Saving Recommended Windows:
Just like washing machines and freezers, windows are energy rated by the British Fenestration Ratings Council on a scale of A-G. Windows achieving a rating of C and above are endorsed by the Energy Saving Trust’s Energy Saving Recommended (ESR) scheme and carry the EST’s swing tag logo.

Make sure you ask for windows with the Energy Saving Recommended logo and Warm Edge Spacer inside to ensure the best energy efficiency.


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Technical Information - However you use glass it is essential for safety and performance reasons that it is correctly specified and installed. Common areas of impact risk, where it is recommended that impact safety glass to BS 6206 is installed, include: Glazed doors, Glazing adjacent to doors, Low level glazing, Bathroom areas, Protective barriers, Furniture and cabinets.

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