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Diamond Windows are a registered FENSA installers

We adhere to a strict code of quality. We notify FENSA whenever an installation has been completed.

Alitherm 300 Windows

Alitherm 300 windows are a particularly versatile solution, providing something for residential and commercial applications alike. Whether you’re looking to incorporate conventional casement windows or modern windows, each style can be achieved with Alitherm 300 windows.

They are ideal for insulation as the polyamide thermal break technology forms a barrier between the warm air inside and the cold air outside. As a result, thermal transmittance is significantly reduced, whilst the U Value is enhanced. Consequently, these windows are built with Document L 2010 in mind.

Alitherm 300 windows adhere to British Standard Kitemarked system KM 81580 KM 81543, which includes an extended polyamide thermal break. It’s this that aids the U Value of the product, which is responsible for Alitherm 300’s ‘A’ Rating in terms of energy. This system is appropriate for internal and external uses alike.


Our range of Alitherm 300 windows is available in a variety of colours, finishes, and even customisable designs. You can opt for externally or internally beaded solutions depending on whether you’re after a traditional or modern appearance. Similarly, there is a selection of available add-ons, including bay-poles, ancillary profiles, and cills.


The versatility continues as far as the installation process is concerned, as Alitherm 300 can be installed as top hung, side hung, or fixed light windows. These are the ideal candidates for replacing old windows for a multitude of reasons, with the energy efficiency being just one.



Anthracite Grey

Anthracite Grey on White


Not only are Alitherm 300 windows energy efficient and great to look at, but they also offer superior protection from intruders. These windows are engineered with incredible security technology, meaning you can feel confident that your home is protected.


Brand Alitherm
NBS Available Yes
Thermally Broken Yes
Dual Colour Yes
Material Polyamide


BS 4873 Yes
BS 7950 Yes
BS 6375-1:2009 Yes
Kitemark Yes
Document L Compliant Yes
U Value 1.5W/m²K (using correct glass unit)
WER Rating A


Frame Depth (mm) 53mm & 70mm
Glazing (mm) 24mm, 28mm, 32mm, and 36mm double or triple glazed units
Top Hung Max Height (mm) 1300mm
Top Hung Max Width (mm) 1400mm
Side Hung Max Height (mm) 1400mm
Side Hung Max Width (mm) 700mm

10 Year Guarantee

All of our double-glazed casement windows are easy to maintain and keep looking like new, partly due to their durability and longevity. We’re so confident in our windows that we offer a ten-year guarantee as standard.

Shop Alitherm 300 Windows with Diamond Windows

Here at Diamond Windows, we’re the leading double-glazing specialists covering the West Midlands. Contact us today to learn more about our Alitherm 300 collection or any other window solutions.

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Contact us
Diamond Windows, Unit 22, Northstreet I.E, Droitwich,West Midlands, WR9 8JB
Company Reg: 5367399
Open Hours
Mon to Fri: 9am to 4.30pm
Sat: 9am-1pm
Sun: By appointment