How does double glazing work?

November 2018

Find out exactly how double glazing works, the ins and outs of their energy ratings and how improving your windows will help you save money and reduce sound pollution.

What is double glazing?

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Double-glazing is a window consisting of two panes of glass separated by a layer of trapped argon gas. The layer of argon gas has 67% of thermal conductivity of air, making it a poor conductor of heat, thus keeping warm air trapped inside your home and helping improve energy efficiency.

This extra pane of glass also acts as a secondary barrier to noise, helping keep your home nice and quiet, and strengthens the window to improve security.


Does double glazing keep out noise?

Yes, it does! While it won’t completely block out all noise, installing double glazing can significantly reduce the noise you hear from outside. The amount of noise the windows blocks out can depend on factors including vent size, the age of the windows, etc.


Does double glazing reduce your utility bills and energy usage?

If you’re replacing older units you can be pretty confident it will save energy and therefore money on your bills. Did you know that our homes account for a quarter of all CO2 emissions in the UK and windows can account for up to 30% of the total heat lost from a house? ‘A’ Rated windows can have a zero energy loss over a year cycle or even add energy back into the room via solar gain. As an example, a detached house with 23.7m² of windows and electric heating upgrading from single glazed wooden windows to A-rated casement windows could save £325.26 a year.


What do the window energy ratings mean?

When buying new windows, one of the most important things to look out for is the Windows Energy Rating (WER). They work in a similar way to the energy ratings on electrical goods.

The ratings go from A (very efficient) to G (incredibly inefficient). To comply with building regulations, all windows have to be at least C-rated.

The Windows Energy Rating is calculated using various values:

  • Thermal Transmittance (U value)
  • Solar factor (G value)
  • Air Leakage (L value)

U-value – how much heat can escape through the glass (thermal transmittance), measured in Kilowatt-hours, per square meter, per year.

For example: 2.5kWh/m2.K

This means that 2.5 kilowatts of energy is lost through every square metre of the window every year – that’s every square metre of window boiling the kettle!

G-value – how much energy gained through your windows from the Sun (solar factor). This is measured in kilowatt hours per metre, per year.

L-value – Air leakage through the window. We’re looking for as low as possible here and is measured in kilowatt hours per metre, per year.

We pride ourselves on only providing the best products, with an official  WER ‘A’ Rating on all of our window products.


Kommerling WER +8


Why do I get condensation on my windows?

Having double glazing should reduce condensation and mist build-up as the inner pane is warmer than the outer pane, thus acting as a heat barrier. However, if you are noticing condensation or mist forming in between the panes of glass in your double glazing, then this could be a sign that there is a fault with the sealed unit.

Even the smallest hole can let air pass through, increasing the chances of moisture build-up.

Don’t worry if you are seeing condensation on the outside pane of glass, this is a good sign! It actually shows how well your windows are performing as the heat from within your home isn’t escaping, keeping the outer pane cooler than the outside air.

Condensation on the internal pane of glass is different and could be a signifier of poor ventilation. For example, if you don’t have an extractor fan in the bathroom, then moisture from the bath and shower will settle as condensation. Opening a window can help reduce condensation until the problem is fixed.


Why am I getting a draught from my double glazing?

Your double-glazed windows are sealed units so should not let any draughts in. If you are feeling a draught from your windows, it might be as simple as a vent being open or it could be more serious, like a fault in the seal around the window frame. Make sure that the PVCu frame is airtight to the brickwork.

If you have a window that opens, then a draught could be caused by the window not being shut properly. A simple check would be to see that there are no faults with the locking mechanism and that the window fits snuggly against the PVCu frame when closed. Any gaps could let in air and cause a draught.



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