🪟 Alitherm 300 vs 400 vs 700 vs 800 — Which Aluminium Window System Is Right for Your Project?
When it comes to aluminium windows, choosing the right system can make a huge difference to the performance, cost and overall success of a project. The Alitherm range from Smart Architectural Aluminium is one of the most widely used in the UK, offering solutions for everything from standard residential homes to high-traffic commercial environments.
But with multiple systems in the family — Alitherm 300, 400, 700 and 800 — understanding the strengths of each is key to selecting the right one.
Below is a clear, no-nonsense guide to help you decide.
🔹 Alitherm 300 — The go-to choice for standard residential windows
Alitherm 300 is the most popular system in the range, and for good reason. It balances performance, slim sightlines and cost-effectiveness, making it the ideal choice for:
- Standard residential properties
- Home renovations and extensions
- Builders/developers working within budgets
- Projects where style and value are equally important
Despite its competitive price point, Alitherm 300 offers excellent thermal efficiency when paired with the correct glass and is fully compliant for residential use. It is also available in a wide range of configurations — including casement, fixed light and tilt-before-turn.
🟢 Best choice when: you want premium aluminium aesthetics and performance without unnecessary extra cost.
🔹 Alitherm 400 — For enhanced energy performance
Alitherm 400 builds on the 300 with a new-generation thermally improved profile, developed to support modern energy-efficiency requirements — including Part L compliance.
It is ideal for:
- New-build properties
- Developers wanting to future-proof energy performance
- Specifiers who need the next level of U-value improvement
Alitherm 400 offers a very similar appearance to 300, but with additional thermal refinement.
🟢 Best choice when: energy performance is the priority or the project is governed by modern Part L requirements.
🔹 Alitherm 700 — Residential plus light commercial capability
If a project requires wider openings, larger sashes or increased durability, Alitherm 700 steps into the spotlight. This system is designed for:
- Higher-end residential projects
- Apartments and multi-residential developments
- Light commercial environments
- Installations where larger/heavier glass units are specified
It retains clean contemporary aesthetics while providing a stronger, more robust operating performance than 300/400.
🟢 Best choice when: you need the capability to support bigger, heavier or more demanding glazing.
🔹 Alitherm 800 — Built for commercial performance
Alitherm 800 is the heavyweight system in the family — usually a flush alternative system for high end heritage and residential applications.
- High End Projects
- Heritage Projects
- Commercial properties
It is designed for durability and ongoing performance in demanding environments where reliability and safety are paramount.
🟢 Best choice when: the project involves premium, heritage and light-use commercial spaces.
🧠 Quick decision guide
| Project requirement | Best match |
|---|---|
| Standard house / extension | Alitherm 300 |
| New-build with energy-efficiency focus | Alitherm 400 |
| High-end residential or larger sash sizes | Alitherm 700 |
| High End residential, flush, heritage projects, commerical projects | Alitherm 800 |
💭 Final takeaway
All four systems deliver performance, aesthetics and longevity, but they are not designed to do the same job.
If you’re working on a standard house or extension, Alitherm 300 is typically the smartest and most economical choice.
You only step up to 400, 700 or 800 when the performance or building type requires it — not the other way around.
📞 Need more advice?
Our technical team are happy to advise on the most suitable Alitherm system for your project — whether you’re an installer, architect, developer or homeowner.
👉 Contact us for specification support, pricing or project advice.
📍 Book a visit to our 210m² showroom to view every system in person.
