Alitherm 400 Aluminium Windows | Slimline Modern Windows UK - national supply, survey and installation
Call us: 020 341 10038 | 01768 254552
Email: projects@thefenestrationnetwork.co.uk
The Alitherm 400 window system is a modern, highly efficient aluminium window designed to suit both contemporary and traditional UK properties.
A Smarts Aluminium system, it delivers durability, slim sightlines and excellent thermal performance — all while providing a clean, modern aesthetic.
What Are Alitherm 400 Windows?
Alitherm 400 is part of the latest generation of thermally broken aluminium windows, replacing older Alitherm 300 / 600 series with enhanced performance, improved security and smoother operation.
It’s versatile, cost-effective, and extremely popular for residential homes and small commercial applications.
Key Features & Technical Summary
System depth - 70mm
Sightlines - Contemporary slim frame
Thermal performance - Low U-values (dependent on glazing)
Glazing - Double or triple glazing options
Security - PAS 24 option / Secured by Design
Operation - Side / top hung, fixed, tilt & turn
Finishes - 150+ RAL colours, dual colour available
Hardware - Modern & discreet handle options
Benefits of the Alitherm 400 System
- Great balance of performance & cost — excellent value without compromise
- Slim modern appearance — ideal for refurbishments & new builds
- High energy efficiency — compliant with Part L regulations
- Low maintenance aluminium — no swelling, warping or repainting
- Strong & secure — meets security standards when specified
- Versatile configurations — fits almost any architectural style
- Perfect partner for aluminium doors on the same façade
Ideal Applications
- Residential properties (modern or traditional)
- Extensions and glazed refurbishments
- New-build developments
- Coastal / exposed environments needing resilience
- Homes upgrading from uPVC or timber
- Mixed-material façade systems pairing with bifolds/sliders
Why Choose Us to Supply & Install Alitherm 400?
We offer a complete service nationwide:
- Technical advice & design support
- Site survey & measurements
- Bespoke UK manufacturing
- Professional installation
- Aftercare & warranty
We supply directly to homeowners, self-builders, architects, contractors, and property developers.
Related Systems & Alternatives
Looking for other aluminium window styles?
- Heritage / steel-look windows (AW-47 system)
- Slimline premium systems (GW70 / Cortizo)
- Matching aluminium doors for cohesive aesthetics
Alitherm 400 Windows — Supplied & Installed Across the UK
We supply and install the Alitherm 400 aluminium window system nationwide, bringing high performance, modern aesthetics and specialist installation to both residential and light-commercial properties.
South & South East
Alitherm 400 Windows London, Kent, Surrey, Sussex, Hampshire, Southampton, Home Counties and Essex.
Whether you’re upgrading a townhouse in London, restoring a property in the Home Counties or installing new windows along the coast, our South & South East team provide full supply, installation and after-care.
South West & West
Alitherm 400 Windows Devon, Bristol and Gloucester.
In the South West region we support new build projects, renovations and heritage conversions, delivering the Alitherm 400 system with precision and professional service for your property.
Midlands & Central
Alitherm 400 Windows Birmingham, The Midlands, Northamptonshire, Nottinghamshire, Leicestershire, Derbyshire and Lincolnshire.
Our Midlands installation teams offer efficient lead-times, experienced surveyors and reliable fitting of the Alitherm 400 system across a wide range of project types.
North West
Alitherm 400 Windows Greater Manchester, Manchester, Lancashire, Liverpool, Cheshire, Cumbria and Carlisle.
From urban apartments to countryside homes and commercial refurbishments in the North West, we deliver the Alitherm 400 windows with local knowledge and full project support.
Yorkshire & North East
Alitherm 400 Windows Yorkshire, Newcastle and the North East.
Whether you’re renovating in Yorkshire, fitting new build windows in the North East or specifying high-end aluminium systems, our teams install the Alitherm 400 window system with full specification, colour and hardware choice.
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PUTTING YOUR MIND AT EASE...
A British Standard that specifies the security performance requirements for doors and windows
the official police security initiative that works to improve the security of buildings and their immediate surroundings
A British Standard that specifies the security performance requirements for doors and windows
quality glazing products, manufactured right here in the UK
the official police security initiative that works to improve the security of buildings and their immediate surroundings
A British Standard that specifies the security performance requirements for doors and windows
the official police security initiative that works to improve the security of buildings and their immediate surroundings
the official police security initiative that works to improve the security of buildings and their immediate surroundings
the official police security initiative that works to improve the security of buildings and their immediate surroundings
10% off all orders placed before 30th November 2025
Applicable only to orders resulting from new quotes produced from 15th October to 30th November, must include full supply, survey and installation and must include any combination of the below:
Windows/ Bi Folding Doors/ Sliding Doors/ French Doors/ Entrance Doors/ Windows/ Garden Studios, Glass Balustrades, Orangeries.