A Rated Glazing

A Rated Double Glazing

What exactly is A Rated Double Glazing?
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Double Glazing

It’s difficult to imagine that less than thirty or forty years ago most of us had single pane windows and endured costly and often uncomfortable heat loss during the winter months. Fortunately, nowadays, we have double or even triple glazing to thank for increases in our energy efficiency, something that saves us plenty of money, as well as keeping us comfortably warm.

As a long term investment with a substantial initial outlay, double glazing is one of the most popular improvements home owners opt for in addition to cavity wall and loft insulation. Without these initiatives, introducing more economical heating systems and energy efficient measures simply don’t work. You might say that double glazing is an integral part of the foundations on which the rest of our home eco-strategy rests.

front of house with double glazing
front of house with double glazing
front of house with double glazing

How does it work?

In double glazing, two panes of glass are combined with a layer of gas in between which acts as an insulator. Glass is a pretty good conductor of heat, which is why there is so much loss when only single panes are used in our windows. Introducing that layer of gas makes all the difference.

One of the important parts of the window is the seal – if this is not complete then air can get into the gap and cause condensation. Cheaper window designs often suffer from this problem, looking great in the first few months or years but then developing problems when air gets in.

For most UK homes, double glazing is sufficient but if you want to pay an extra premium, and have more insulation, you can find certain companies who deliver triple glazed windows.

The glass can be coated with a low emissivity metallic layer that reflects more heat back into a room. Many windows are now incorporating this innovation as a matter of course but anything over 10 years old may not have this. All windows produced in the UK must comply with European Union legislation which means they should be marked with the CE logo that ensures they are compliant.

The energy efficiency of a particular window design is determined by its R Value. A single pane window may have an R value of around 0.15 whilst uPVC windows will have a level of 0.50 or more. Essentially the higher the R value, the more energy efficient it is.

The benefits of double glazing

  • Double or triple glazing greatly reduces the amount of heat lost through your windows.
  • It not only keeps you warm in winter but cooler in hot summers.
  • Double glazing greatly reduces the amount of noise from outside, particularly important if you live near a busy road.
  • Double glazed windows reduce condensation by keeping the temperature in your room relatively constant.
  • They make your home more secure. It is difficult to break into with the double layer of strengthened glass and the addition of the secure locks used nowadays.
  • They increase the resale value of your house – people are less likely to make a good offer if they know they have to spend money and time on installing double glazing.

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Energy Efficient & Double Glazing

Energy savings are measured over A, B and C ratings, with A being the most efficient. The rating will all depend on how your window is made up. Windows also have a U value that shows how much heat they let through – a lower U value suggests greater energy efficiency than a high one (as opposed to a higher R value).

The glass is important in double glazing and if you want the best then you need a product with low emissivity – usually a coating of metal oxide that allows light to come in but then stops the heat escaping to the outside. The gas that is used between the glass panes can also vary. Heavy gases such as argon are less conductive and provide better insulation but are more expensive. The spacers which keep the panes separated contribute to efficiency and non-metallic ones are better than something like aluminium which is more often used in large office blocks.

There are various energy efficient solutions on the market and being aware of them can help when it comes to selecting the right supplier or installer.

  • Gases: First of all, the gap between the two window panes in double glazing is not air. It is usually an inert gas such as argon or krypton which are better thermal insulators. Because the gasses are inert they are harmless if they escape into the atmosphere so you are not putting yourself or your family in harm’s way by choosing them.
  • Heat Absorbent Glass: Many double glazing products now have tinted glass that absorbs some of the solar radiation coming from outside. There are various types but they do not generally impact on the U Factor for windows.
  • Low Emissivity Coated Glass: One of the more recent developments in glazing technology, low-e windows can reduce heat loss by as much as 30 to 40%. It is a very thin layer of microscopic metal or oxide that is invisible to the naked eye and is usually added during the manufacturing process. All A rated windows, the most efficient, will have a low-e coating which makes them slightly more expensive than normal windows.
  • Reflective and Spectrally Selective Glazing: These are coatings that reduce the amount or type of light that comes through your window and are more applicable to hotter climes than the UK. Reflective coatings reduce the amount of solar radiation and glare coming through your window. Spectrally selective glazing uses a type of low-e coating that is more generally designed to reduce infrared heat.
  • You can save between £150 and £300 PA with a DG upgrade so it’s not really about payback time its more about knowing you’re not throwing your money out of the window and peace of mind.

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All properties lose heat through their windows

But energy-efficient glazing keeps your home warmer and quieter as well as reducing your energy bills. That might mean double or triple glazing, secondary glazing.

A more comfortable home: energy-efficient glazing reduces heat loss through windows and means fewer draughts and cold spots.

  • Peace and quiet: as well as keeping the heat in, energy efficient-windows insulate your home against outside noise.
  • Smaller energy bills: replacing all glazed windows with A-rated double glazing could save you around £270 per year on your energy bills or 26% on heating bills.
  • By simply using a C rated window or above the amount of energy lost through windows by up to 90%. That’s enough energy to;
    - Run 9 televisions for a year *
    - Drive over 600 miles in an average sized car *
    - make 34,000 cups of tea *
    (* estimates by energy.gov)
  • A smaller carbon footprint: by using less fuel, you’ll generate less of the carbon dioxide that leads to global warming - typically, 680kg a year.

How energy-efficient glazing works

Double-glazed windows have two sheets of glass with a gap between them, usually about 16mm, to create an insulating barrier that keeps the heat in - sometimes filled with Argon gas.

Triple-glazed windows have three sheets of glass, but aren’t always better than double-glazed windows.

The problems with old sealed units:

Most energy-efficient glass for double glazing is low emissivity (Low-E) glass. This often has an unnoticeable coating of metal oxide, normally on one of the internal panes next to the gap. This lets in light and heat but cuts the amount of heat that can get out.

In Between

Very efficient windows might use gases such as argon, xenon or krypton in the gap between the sheets of glass, with the gas inserted the glass is capable of achieving an A rating on the WER (Window Energy Rating).

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