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Everything you need to know before buying Windows, Doors or a Conservatory

Low-E Glass

What does Low-E mean?

Low-e stand for low emissivity and is the relative ability of it's surface to emit energy by radiation. In laymans terms “Low-e” reflects IR light (heat energy) and stops it passing through.

What is Low-E glass?

Low-e glass is just a coating applied to the inside of a pane of glass. The “low-e” coatings are microscopically thin, virtually invisible, metal or metallic oxide layers. When they installed on the surface of a double glazed unit the Low E coating will reflect IR heat from inside the room from central heating or fires to help reduce the energy loss when it is cold outside, thereby reducing heating costs. The better the low-e coating the lower the U-Value and is reported to make a double glazed unit as effective as a triple glazed unit.

Low-E Glass Hard Coat vs Soft Coat

There are two main types of Low-e glass, hard coating and soft coating.  Hard coat Low-E glass is produced by pouring a thin layer of molten metal, usually tin onto a sheet of glass while the glass is still slightly molten. The tin actually becomes fused to the glass. This process makes it difficult or "hard" to scratch or remove the tin. Often this glass has a blue or grey tint to it and is more expensive to produce.

Soft coat Low-E glass involves the application of atomized silver, zinc or tin or other precious metals to glass in a vacuum. The glass enters a vacuum chamber filled with an inert gas which is electrically charged. The electricity combined with the vacuum allows molecules of metal to be sprayed onto the glass just like gold platting metal. The coating is fairly delicate or "soft." however this is on the inside of the sealed unit so this is only an issue until the until is made.

Well know types of low-e Glass

Below are the major manufactures of low-e glass in the UK

Pilkingtons K Glass (Hardcoat)

Saint Gobain planitherm (Softcoat)

How much money will Low-e glass save?

Because low-e glass stops energy from escaping it can save you money on your heating bills, below is a table based on a typical 3 bedroom semi detached property located in the midland area with different types of UPVC windows.

 

Annual Space heating cost

Annual saving compared to single glazing

Single Glazing

£194

-

Convential Double Glazing

£152

£42

Double Glazing with softcoat Low-e

£126

£68

Is it a legal requirement to have Low-E Glass in New Windows?

While it is not a legal requirement to have low-e on new windows installed in the UK since Document L in 2002 it is almost impossible to reach the required u-value of 1.8 W/m²K without it. However low-e glass does not increase solar gain and low iron glass is required for that to achieve the new ‘A’ ratings

Is low-E glass glass effected by Lead windows or Georgian Bars?

Yes these can effect the rate in which energy is lost from a double glazed unit however if you property required either of these things it is far better to have Low-e than not to have Low-e glass.

 

What is Low-e and why does it help the U-value of windows

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