Thermal Efficiency Guide


Continually rising energy costs mean installing thermal efficiency systems is increasingly important.

Clearview secondary glazing improves the comfort of your home and helps to reduce your heating bills, reducing energy consumption and carbon emissions. Clearview’s systems are renowned for their thermal efficiency performance and can be further enhanced by utilising Pilkington K or Low E glazing. After Clearview secondary glazing is installed, a thermal efficiency saving of 60-70% is achievable.

Secondary Glazing Thermal Facts

1. Single pane glazing in buildings is a major factor in heat loss

2. Secondary glazing is ideal for listed buildings, period property and buildings in conservation areas

3. Installing secondary glazing increases energy efficiency and reduces fuel bills

4. Energy efficiency helps safeguard our environment for future generations

5. Efficient secondary glazing can improve the thermal performance of a window by more than 60%

6. Installing secondary glazing can give an annual fuel bill cost saving of up to 15%

7. Secondary glazing means you can seal the gap tighter and see the savings

How is the thermal efficiency of primary windows calculated?

Each building is unique, its construction, window style and age. Primary window glass impacts on thermal efficiency, as does effectiveness of heating systems and other existing insulation. Because of this, it isn’t possible to give precise thermal efficiency data for a specific building. To benchmark thermal efficiency in a broad form, a European standard has been set: The CEN sized window is 1230mm x 1480mm (1.82m squared), is timber framed, single glazed. The thermal performance of that window is calculated in accordance with a European standard: EN ISO 10077 for the window frame, and EN410 for the glass, and is measured in Watts per Metre Squared- Kelvin w/m2K. Watt is a unit of energy measure, M is the area of the window: width x height, Kelvin is the difference in temperature from the inside to the outside, or the rate of heat loss per metre square of product per 1º difference between external temperature and internal temperature. This enables the window’s thermal performance to be calculated and presented – often referred to as the window’s Uvalue. Simply put, the lower the Uvalue, the better a window is performing in terms of preventing heat loss.

Thermal performance. It’s all about the U-values

A U-value is a measure of how much heat will pass through a thermal object, a window or wall. Low U-values means little heat will passes through, therefore it’s energy efficient. U-value is measured in W/m2K – that is, Watts per square metre per degree Kelvin (1º Kelvin is the same as 1º Centigrade, but with a different zero). So if a wall has a U-value of 1.0, then 1 m2 of wall will let 1 Watt pass through it when there is a temperature difference of 1 degree between the inside and outside. Secondary glazing can yield U-values as low as 0.6, which is more thermally effective than double glazing.

What’s the most effective way of preventing heat loss through a single glazed window?

The chart shown here is a excerpt from tests commissioned by Historic Scotland, and can be seen their document ‘Thermal performance of Traditional Windows’. The chart illustrates the reduction in heat loss through single glazing with option compared to single glazing only. Historic Scotland say: “Installing the secondary glazing clearly gives an improvement which is comparable to the best of the options examined prior to its installation, however the secondary glazing has the advantage that its benefits can be realised both day and night. Augmenting the secondary glazing with the other options gives further improvement, however the insulated shutters give only a small improvement over the original (uninsulated) shutters.”

For more information and help on secondary glazing and thermal insulation, email: [email protected]

Discover How To Stop Draughts for Good And Save On Your Energy Bills

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Clearview secondary glazing - the solution to significantly improved acoustic and heat insulation to your property, making your home or offices more comfortable, secure, greener and cost efficient to run. Achieved without the disruption of replacement windows, and without damaging the character of your building.

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