Alitherm 400 is a high-performance aluminium window and door system designed for modern residential and commercial applications. Fully compliant with Document L of the Building Regulations, it delivers excellent thermal efficiency, enhanced security, and a stylish design. With PAS 24 approval, a wide range of colour options, and a new Quick-Glaze Bead for faster installation, Alitherm 400 offers a practical and visually appealing solution for new builds and refurbishments.
In producing this review, we’ve seen Alitherm windows made at manufacturers in Hainault and in-situ in installer showrooms. We’ve also seen the product fitted in dwellings, commercial and apartment buildings. The technical and fabrication manuals are also studied.
Smart Systems Alitherm 400 Windows
A well rounded window system, available in casement, steel look, flush, tilt and turn and fixed window options. Good styling, slim sightlines and a matching door system. Smart Systems windows and doors can be vague on their U-Value, so make sure you check these.
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Pros
- Widely Available
- A choice of window styling under one collection.
- Matching doors are just as good.
- Good styling and sightlines.
- Hidden Trickle Vent option.
Cons
- Expect inconsistent pricing, from low to high.
- Who makes it determines the quality you get.
What are Alitherm 400 Windows?
Extruded and coated by Smart Systems, the Alitherm 400 is an up-to-date system in a variety of configurations with a matching hinged door, which makes it appealing as a complete window and door system.
Designed to replace dated metal, plastic, or wood windows as well as newly built openings, Alitherm is widely available throughout the UK in many showrooms. You’ll have no trouble finding a manufacturer, supplier or installer of these windows, or you can get in touch for details of your nearest.
Smart Systems has designed Alitherm 400 with all the window styling and opening options, including fixed, side or top hung open out, flush sash, heritage style and tilt and turn windows. It’s mostly a residential system for dwellings, but there’s no reason it can’t also be used in commercial buildings as well.
Design and Aesthetics
The Alitherm 400 window system is designed to offer both performance and ease of installation, making it a great choice whether you’re replacing old windows or fitting new ones. Its advanced thermal insulation, thanks to polyamide thermal breaks and low-line gaskets, helps keep your home warm while reducing energy costs.
With the right double glazing, it can achieve an ‘A’ Window Energy Rating, meaning better comfort and lower bills. The system also includes Quick-Glaze beads, which simplify the glazing process, making installations quicker and more efficient.
Built from high-quality aluminium extruded profiles, these windows are strong, durable, and resistant to weathering. The frames are precisely cut and joined using advanced crimping techniques, ensuring a robust and secure structure. Thoughtful design features, like built-in drainage and ventilation, help protect against moisture and weather damage, extending the lifespan of your windows. If you’re concerned about security, the system supports multi-point locking, giving you extra peace of mind. For homeowners, this means you get a stylish, energy-efficient, and secure window system that’s built to last.
Installers benefit from a well-designed system that’s available everywhere and easy to fit, whether in a factory or on-site. The choice of glazing options—internal, external, or Quick-Glaze—allows flexibility depending on the project. This means the profiles or beads can be provided with the glazing gasket post-extruded into the profile. Beading the windows is simpler and as is often claimed, reduces manufacturing time and time on site fitting the glass.
Alitherm 400 windows and doors feature a slim, contemporary design with a choice of chamfered, flush, standard, and heritage sashes. Their narrow sightlines allow for maximum glass area, creating bright, open spaces with plenty of natural light. Available in any RAL colour, alongside a selection of stock finishes, the system offers dual-colour options for a personalised look.
One of the nicest features of this window is around the trickle vents, which they’ve designed into the system as a more discreet version than the widely used add-on to the window head, adding to the sightline. A similar version exists on the outstanding Elite window made by Aluco and our Product of the Year 2024.
This is a very comprehensive window system with well over 50 different profiles in various styles and designs to cater to most design requirements. For example, there are square and stepped outer frames, with odd leg options for fitting into stone mullions or timber subframes.
Also available is a selection of flush outer frames and sashes, and there are even profiles designed to integrate the window system into commercial curtain walling. There are slimline, heritage and flush sash profiles and options for internal or external glazing.
Alitherm 400 is designed to create large and small windows, as well as integrate with doors and screening. The mullions and transoms available are diverse and include flat, flush, heritage styling, and French casement.
You’ll also find larger reinforced mullion sections, intended for when floor-to-ceiling windows or windows with fixed pages are needed.
Alitherm 400 Windows Sightlines
This can be comfortably regarded as a slimline window system, but the sightlines you get very much depend on the frame and sash configuration and whether your new windows are going into new or existing openings.
A fixed window with just its outer frame provides a pleasing 42mm sightline (49mm with a longer leg frame). Add a dummy sash, and this increases to 59mm typically. Where you have opening sashes, sightlines range from 68mm at the slimmest versions to 71.5mm, up to 81.5mm, again depending on the frame and sash combination you need.
Transoms and mullions range in sizes from 50mm, 57mm, 62mm up to 116mm for deeper profiles.
A trickle vent at the top of a window adds 42mm, which is what you can expect in pretty much every installation.
Technical Information
Full technical information is available on the Smart Systems Website. However, the entire system is now much more advanced than the Alitherm 300 system it replaces. Here’s a summary of it’s key technical specs.
- Frame depth: 70mm.
- Glazing options: 24mm – 45mm (double or triple glazing).
- Maximum sash sizes:
- Side-hung: 864mm x 1400mm.
- Top-hung: 1400mm x 1400mm.
- Fixed: 2100mm x 2100mm.
- Tilt & Turn: 1200mm x 2100mm.
- Single doors: 1100mm x 2400mm.
- Double doors: 2200mm x 2400mm.
- Thermal efficiency: U-values as low as 1.4 W/m²K.
- Acoustic insulation: Rw up to 45 dB.
- Weather resistance:
- Air permeability: Class 4.
- Water tightness: Class AE2400.
- Wind resistance: Class 2000+.
Alitherm 400 Windows Security and Energy Efficiency
Alitherm 400 meets the latest PAS 24 security standards, ensuring strong protection against forced entry. Multi-point locking systems, durable aluminium frames, and secure glazing options enhance security, making it suitable for residential and commercial properties.
As so many factories make this product, we know Smart Systems are quite strict with fabricators who don’t provide Smart-supplied handles, hardware and other components. You’ll find some fabricators add their own sourced brand and styles of handles, creating a different-looking window alongside alternative hinges and other components. This does not matter and should not dissuade you.
How Much Does the Alitherm 400 System Cost?
You can find out more about typical costs of aluminium windows here. Our recommendation would be to avoid approximate prices and get accurate window quotations based on your window types and sizes, colours, glass specifications and designs. Where your windows are being fitted also affects the price you pay. Get in touch for more information and advice.
Other Products to Compare with Alitherm 400
- Aluco Elite for Steel Look Windows
- Cortizo Casement Windows for opening outwards or tilt and turn options. Read our Cortizo Windows Review.
- Origin OW-70 windows for standard slimline casements.
- Aluk 58 BW windows.
Alitherm 400 vs 300 what’s the difference?
While they share similarities in aesthetics and thermal efficiency, Alitherm 400 offers enhanced performance, security, and installation benefits, making it a more advanced option. The Alitherm 400 is fully compliant with the latest Document L regulations double glazed, achieving U-values as low as 1.4 W/m²K, compared to the Alitherm 300’s 1.5 W/m²K. Additionally, Alitherm 400 is PAS 24:2022 certified, providing a higher level of security, whereas Alitherm 300 requires additional upgrades to meet the same security standard.
The Alitherm 400 and Alitherm 300 are both available but our advice would be to now avoid the 300 system on U-Values, unless it is triple glazed with documentary proof of compliance. This is a newly introduced window system, designed to address the future changes to Building Regulations, meaning U-Values of windows are getting lower and more demanding. Smart Systems are vague on how their windows meet specific U-Values, often resorting to the very lazy statement around meeting U Values and Window Energy Ratings when used in conjunction with the correct double-glazed unit. But, rarely telling you what the double-glazed unit specification should be. Meeting U-Values for your project IS important. So don’t just accept what a salesman may tell you about thermal performance. Ask for documented or written confirmation. Or get in touch with us for advice. The BFRC Website does show A, B and C ratings for this system.
A key difference is the introduction of Smart’s Quick-Glaze Bead in the Alitherm 400, significantly reducing fabrication and installation time. The Alitherm 300, while still a strong contender, uses a more traditional glazing method, making it slightly more labour-intensive to install. Both systems offer slim sightlines, various sash styles (including flush casements), and a wide choice of colours, but Alitherm 400 provides greater versatility, including a tilt and turn option, which is not available in the Alitherm 300 range. Overall, while Alitherm 300 remains a reliable and cost-effective choice, the Alitherm 400 offers superior thermal efficiency, security, and ease of installation, making it the better long-term investment for modern projects.
More information, where to view and buy Alitherm 400 windows.
Alitherm 400 is a versatile, energy-efficient, and secure aluminium window and door system that offers modern aesthetics, high security, and excellent performance.
Its wide range of window styles, from contemporary, to slimline, heritage, flush, tilt and turn and steel look, provides great choice within one system. The Alitherm 400 doors are also excellent.
Suitable for both resdiential or light commercial projects, Alitherm 400 is easy to make, quick to glaze and install and for end users a very pretty collection of windows and comes recommended.
Contact us for more information, prices and where to view and buy Smart Systems Alitherm 400 windows near you.
Images courtesy of Chigwell Group and Chigwell Window Centre, manufacturers and installers of aluminium, and PVCu windows and doors.
