How Does Double Glazing Save Energy?

We have created this guide to explain how double-glazed windows are energy-efficient, how much energy they might save for your property, and offered some tips on what you can do to ensure your home saves as much energy as possible.

Why are Double-Glazed Windows Energy-Efficient?

Double-glazed windows are energy-efficient because of heat conduction. When heat is lost through a window, said heat needs a surface to get transferred or conducted through. Double-glazed windows have two glass surfaces, and between these is a layer of gas. Normally this gas will be Argon, which is a poor conductor of heat. Because of this, not as much heat will make it through to the outside pane of glass. 

Below, we have separated this explanation in order to explore the science behind double-glazed windows’ energy efficiency.

Controlling the Temperature

Because having two panes of glass with Argon gas between acts as a poor conductor of heat, double-glazed windows are excellent at controlling the temperature in a room. The temperature in the interior remains mostly unaffected by the temperature outside, meaning cold areas are kept cold and warm areas are kept warm. This is done without the need for the use of heating or cooling systems.

Reflective E-Coatings

Glass panes on double-glazed windows have a reflective e-coating. This is a reflective material which coats the inner side of each pane and is designed to reflect the heat back to where it came from to reduce heat loss from within a property. Having this e-coating adds another barrier that poorly conducts heat, meaning more heat is kept within the room.

Reducing Heat Conduction

When molecules are heated, they begin to move quickly and conduct (or pass) the heat to each other. When molecules are trapped in a thin layer between two glass surfaces, these molecules are kept close to one another. This allows for an easier heat transfer. Outside of the two glass surfaces, molecules that are not kept close together and are instead spread out will have a much slower rate of heat transfer. As a result, the thin layer of air in double-glazed windows acts as a method of heat insulation.

In essence, making an extremely thin gap for air to pass through prevents it from circulating properly, resulting in a lower amount of heat conduction. This does not mean that heat loss is avoided entirely, it simply means that this heat loss is slowed down by a significant amount.

Reducing Noise Pollution

As the panes of glass in double-glazing don’t make direct contact with one another, soundwaves become dampened. This helps to make a room much quieter inside, though it will not soundproof the room completely.

The Spacer

The gap between the two glass panes of a double-glazed window is called the spacer. These range in size from 6 mm to 20 mm and are usually made out of a material such as fibre, metal, or aluminium. When installing double glazing, it is suggested that anything over 12 mm will be best for preventing heat loss and reducing sound pollution.

What Percentage of Heat is Lost Through Windows?

Experts are slightly divided on how much heat is lost through windows exactly. Most will agree that windows typically account for around 10% of all heat lost in a home, but some say this figure actually goes as high as 18%. 

About two-thirds of the actual amount of heat lost is due to the radiation through glazing. The next largest contributor to heat loss is air leakage, especially from windows with poor insulation. The remaining heat loss after this is mostly due to heat convection through cavities and poor heat conduction through window frames.

How to Calculate Thermal Efficiency in Windows

All glazed windows have something called a U-value. This indicates the window’s level of thermal transmittance, expressed in units of Watts per square metre (m²) per degree of temperature difference. 

The lower the U-value of a window in your home, the more thermally efficient the window is. You should notice a similarity between U-values and the energy labels that are present on many home appliances, rated from A (the lowest or best performing) to G (the highest or worst performing).

It’s also possible for your windows’ performance ratings to be expressed through Window Energy Ratings. This is becoming the more popular method of calculation with modern windows because it offers a simple method of understanding the energy-saving properties of a window.

How Much Energy is Saved with Energy-Efficient Windows?

Depending on the windows installed and the type of home that you have, energy-efficient windows may reduce heat loss by anywhere between 74% and 83%. When translated into money, this might mean saving as little as £50 a year or as much as £235 a year. 

Other Ways to Reduce Heat Loss from Windows

As well as having double or triple glazing in windows, there are also some other methods of preventing heat loss and reducing heating bills in your home:

• Ensuring your windows don’t have gaps (this is a common problem in older or poorly-fitted windows)
• Using polyamide sections between glass panes to help stop heat being conducted through the glazed frame
• Installing thick curtains over the top of your windows to add an extra layer of insulation

Should You Buy Double-Glazed Windows?

Considering the amount of money and energy you would be able to save by having double or even triple-glazed windows installed in your home, the notion is always worth exploring. The windows may cost more to install than single-pane windows, but they will quickly become both cost-effective and value-for-money with energy savings and money taken off your bill. As the windows will be new, they are also less likely to have developed gaps or have lost any of the Argon gas that helps to trap heat within a home.

If the windows are installed by a team of specialists with many years of experience at fitting home improvement features, such as energy-saving windows and doors, there are less likely to be flaws or faults in the final fitting. This also helps to prevent heat loss, as air won’t be able to escape immediately through any gaps that are left behind. It also means you won’t have to spend as much money getting this error corrected, either through someone refitting the windows or having entirely new windows fitted.