Low-E (Low Emissivity) Glass and Thermal Efficiency

What is Low-e glass?

Low emissivity glass is glass that has an undetectable microscopic covering applied to it in order to enhance its thermal performance.

How does Low-e glass improve thermal efficiency?

Low emissivity glass is a vital part of many energy efficient windows and doors. It has a surface finishing that runs as follows:

It enables short wavelength heat from the sun to enter your home through the glazing.

This solar energy works with your domestic heating unit to heat up your space, which then emits long wavelength heat radiation.

A big percentage of that long wave heat would vanish back out through windows made of regular glass. However, the Low-e covering reflects that heat back into your space so the heating unit does not need to work as tough to preserve a comfortable room temperature level.

Will Low-e glass meet the Building Regulations?

Much better than simply fulfilling the Building Regulations, Low-e glass will allow you to both accomplish and exceed the new targets for doors and windows.

What other characteristics should I know?

Whilst there are significant advantages to picking thermally efficient Low-e glass for your house, there can be some negative effects under particular conditions.


Recent developments in developing neutral Low-e coatings reduce the phenomenon of light coloured materials (such as net curtains) appearing slightly darker when viewed through the glass.


This phenomenon may occur sometimes of the day when the sun is at a specific angle or under some lighting conditions. It can likewise be influenced by the type of Low-e covering used.

External condensation

Thermally effective windows are so proficient at keeping the heat in that the outer pane can get cold, as it is no longer being warmed by lost heat.

Under some weather and at specific times of the year, this can result in the development of condensation on the outside surface of the glass. This is a positive indicator of a thermally efficient window.


Depending on coating type, glass substrate and glass density, some minor colour or shade distinctions may be obvious on Low-e glass.

This may be more apparent when one double or triple glazed window unit is changed in a house, as the Low-e finishing will likely be slightly different (i.e. from a different batch) from those on the other window systems.


Specific Low-e glass is good at solar heat gain, harvesting free heat from the sun, helping to lower heating demands. In some circumstances, this can cause overheating leading to an uncomfortable environment.

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