Crittall® vs Smart Heritage Aluminium: A 2026 Comparison

A homeowner’s guide to replacing steel windows. We brutally compare cost, thermal efficiency, and aesthetics across Hampshire and Berkshire.

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Smart Alitherm Heritage aluminium windows perfectly replicate the iconic slim sightlines of traditional steel.

While Smart Heritage aluminium windows are a relatively modern architectural innovation, the iconic, slimline grid-like style they flawlessly replicate has been around for over a century. Genuine Crittall® steel windows span three centuries of British architecture, first rising to prominence in 1884.

However, modern homeowners face a common renovation dilemma: do you choose the highly authentic (but incredibly expensive and high-maintenance) genuine steel, or the modern, cost-effective “Crittall-style” windows made from thermally broken aluminium?

1. The Core Differences at a Glance

Crittall® Windows are the genuine article, manufactured from solid steel. They are the ultimate authentic choice for meticulous heritage restorations, high-end industrial conversions, and classic 1930s Art Deco properties.

Smart Heritage Windows (officially known as the Smarts Alitherm Heritage system) are a modern, highly engineered aluminium alternative. They are specifically designed to physically replicate the ultra-slim profiles of traditional steel, but leverage the immense thermal and maintenance benefits of modern aluminium construction.

2. The Data: Steel vs Aluminium Window Frames

If you are looking at smart alitherm heritage vs crittall, you need to see the raw numbers. Here is exactly how the two manufacturing materials compare for a modern homeowner.

3. Interactive: Steel vs. Aluminium Decision Engine

Not sure if you should pay the premium for real steel? Use our interactive tool below. Enter your property type and your primary goal, and we will instantly calculate which material is the right investment for your specific renovation.

4. Head-to-Head: The 4 Performance Rounds

5. Building Regulations (Document L)

When replacing windows in the UK, you must legally comply with Approved Document L of the Building Regulations, which dictates strict energy efficiency standards (measured in U-Values).

Because steel is a highly conductive metal, it can be incredibly difficult (and consequently very expensive) to manufacture a steel window that meets modern stringent U-Value requirements without making the frames bulky. Conversely, Smart Aluminium Heritage windows easily achieve exceptional U-Values and top Window Energy Ratings (WERs) right out of the box, ensuring your renovation passes building control without a single hitch.

6. Why Choose Smart Alitherm Heritage?

For the vast majority of our customers at KJM, the Smarts Alitherm Heritage aluminium window and door system is the perfect sweet spot between stunning aesthetics, high performance, and sensible pricing.

• Ultra-Slim Profiles: The dimensions are meticulously designed to replicate traditional steel windows without the bulky plastic look of standard uPVC.
• Infinite Colour Choice: While black heritage aluminium windows are our most popular request, they can be powder-coated in literally any RAL colour. You can even specify “dual colour” (e.g., black outside to match period brickwork, white inside to keep rooms bright).
• Authentic Hardware: The illusion is completed with period-accurate hardware. The system is available with traditional “Monkey Tail” and “Bulb” peg stays to match Victorian and Art Deco furniture perfectly.
• High Security: Unlike flimsy historical windows, the modern Alitherm system is rigorously tested to PAS 24 security standards, featuring multi-point locking mechanisms.

7. Local Installations in Hampshire & Berkshire

8. Frequently Asked Questions