Alitherm 400 Windows
ALITHERM 400 WINDOWS
Slim, Secure & Energy-Smart Aluminium Windows
Looking for aluminium windows that tick every box? Alitherm 400 Windows from Smart Systems combine slim sightlines, serious strength, and impressive energy performance in one modern package. At 4Moon Windows, we supply and fit this trusted system for homes and light commercial projects across Croydon, Thornton Heath, and South London. Whether you are replacing tired old frames or planning a full renovation, Smart Alitherm 400 Windows give you a clean, contemporary look that lasts for decades. Slim frames. More glass. More daylight. Less maintenance. It really is that simple.
1.4 W/m²K
U-values with double glazing
1.1 W/m²K
U-values with triple glazing
PAS 24
Certified security standard
200+ RAL Colours
Flexible colour and finish options
Alitherm 400 Windows
What Are Smart Alitherm 400 Windows?
Outstanding Thermal Performance
Alitherm 400 Windows achieve U-values as low as 1.4 W/m²K with double glazing and around 1.1 W/m²K with triple glazing. For an aluminium system, those numbers are excellent. They comfortably meet Part L of the Building Regulations, which many older aluminium windows still struggle to do.
PAS 24 Certified Security
Every Smart Alitherm 400 window is tested to the demanding PAS 24 security standard. Multi-point locking, robust aluminium profiles, and internal glazing beads work together to keep intruders out. For families in busy South London neighbourhoods, that peace of mind matters.
Aluminium Windows UK Homeowners Trust – Built to Last
Not all aluminium windows UK suppliers offer the same quality. The Alitherm 400 stands out because it is designed, extruded, and coated in Britain by Smart Systems, with a track record spanning decades. Aluminium does not warp, rot, rust, or fade. It handles the British weather with ease and typically lasts 30 to 40 years or more. Compare that with uPVC, which can discolour and weaken over time, and the long-term value becomes clear. The system also features Smart's clever Quick-Glaze bead technology. The glazing gasket comes pre-fitted to the bead, so installation is faster, neater, and more reliable. Less time on site means less disruption to your home.
Alitherm 400 Windows
Why Homeowners in Croydon Choose Alitherm 400 Windows
If you are searching for new aluminium windows Croydon homeowners can rely on, the Alitherm 400 deserves a place at the top of your shortlist. Here is why this system consistently outperforms the competition. Aluminium is far stronger than uPVC, so the frames can be slimmer without losing strength. The result? Larger glass areas, brighter rooms, and clean, minimal sightlines that suit both modern and traditional homes.
Why Buy Your Alitherm 400 Windows from 4Moon Windows?
At 4Moon Windows, we do more than supply frames. We manage your project from the first measurement to the final clean-up.
Get Your Free Alitherm 400 Windows Quote Today
Get a Free Quote for New Aluminium Windows in Croydon
Contact 4Moon Windows today for a free, no-obligation quotation and honest advice on the best options for your home and budget. Call us, email us, or request a call back through our website. Your brighter, warmer, more secure home starts here.
FAQ
Frequently Asked Questions
Alitherm 400 Windows typically achieve a U-value of 1.4 W/m²K with double glazing and around 1.1 W/m²K with triple glazing. These figures meet current Part L Building Regulations, making the system fully compliant for replacements, extensions, and new builds.
Yes. Smart Alitherm 400 Windows are tested and approved to the PAS 24 security standard. They feature multi-point locking systems, strong aluminium profiles, and internal glazing beads, giving your home robust protection against forced entry.
Quality aluminium windows like the Alitherm 400 typically last 30 to 40 years or more. Aluminium does not rot, warp, or rust, and the powder-coated finish resists fading. A simple wipe with soapy water a few times a year is all the maintenance they need.
You can choose from over 200 RAL colours, including popular shades such as anthracite grey, jet black, and white. Textured finishes and dual-colour options are also available, so the interior and exterior of your windows can be different colours.
Absolutely. The system is available in flush casement and chamfered profiles, which suit both period and modern homes. Slim frames and a wide colour range make it easy to match the character of Victorian, Edwardian, and contemporary properties across Croydon and South London.