Thermally enhanced steel windows: U-values and use cases (T60 vs W20 TE)

• 1 December 2025
• News

When you’re investing in a new home or high-end renovation, the choice of windows matters far beyond aesthetics. Steel windows have long been celebrated for their slender sightlines and industrial elegance, but historically, they’ve struggled with thermal performance. That’s where thermally enhanced windows transform the story entirely.

Modern thermal break technology allows steel frames to compete with – and often exceed – the energy efficiency of traditional window materials. For architects, specifiers and discerning homeowners, understanding the technical differences between Crittall’s thermally enhanced systems is essential to making an informed decision.

What is a thermally enhanced window frame?

A thermally enhanced window frame incorporates an insulating barrier between the internal and external steel sections. This thermal barrier prevents direct metal-to-metal contact, dramatically reducing heat transfer through the frame. Without this technology, metal frames act as thermal bridges, allowing warm air to escape during colder months and driving up energy costs.

The result? Better insulation, lower energy bills and a significantly reduced carbon footprint – all while maintaining the coveted aesthetic of a traditional steel window.

Understanding U-values and thermal performance

U-values measure how effectively a window prevents heat loss. The lower the U-value, the better the insulation. With energy efficiency now a priority for potential buyers and building regulations alike, achieving optimal U-values isn’t just desirable – it’s often mandatory.

Crittall’s thermally enhanced ranges deliver impressive results:

• T60 thermally enhanced windows achieve U-values as low as 0.8 W/m²K when paired with appropriate double glazing. This performance makes them suitable for both residential and commercial applications where energy efficiency is paramount.
• W20 TE windows incorporate a full thermal break throughout the frame structure, delivering robust overall thermal performance for larger-scale commercial and residential projects.

Both systems prevent the transfer of heat between indoor and outdoor environments, maintaining consistent indoor temperatures year-round.

What’s the difference between T60 and W20 TE?

The T60 range is Crittall’s most thermally advanced residential system. With a 60mm frame depth, it accommodates high-performance glazing units while maintaining slim steel profiles. It’s the smart choice for modern homes, extensions and heritage renovations requiring Part L compliance.

The W20 TE system is engineered for commercial applications and larger residential projects. Built on the robust W20 profile, the TE (thermally enhanced) version incorporates thermal breaks throughout, offering excellent energy transfer control across expansive glazing installations.

Which system suits your project?

Choose T60 if you’re:

• Renovating a period property with conservation considerations
• Building a contemporary new home with demanding energy standards
• Seeking the finest sightlines with maximum thermal performance
• Working on residential projects requiring Building Regulations approval

Choose W20 TE if you’re:

• Specifying commercial glazing systems
• Designing large-scale residential developments
• Creating feature walls or curtain walling applications
• Requiring proven performance across institutional or corporate buildings

Beyond energy efficiency: Additional benefits

Thermally enhanced steel windows deliver more than just lower energy costs. The insulating properties that reduce heat loss also improve sound insulation – a considerable advantage in urban environments. The elimination of cold spots near windows also prevents condensation issues common with older windows or standard frames.

For heritage-conscious clients, thermal break technology means you needn’t compromise between authentic aesthetics and modern building standards. The slender profiles respect original architectural language while meeting contemporary performance expectations.

Making the smart choice for your project

Investing in high-performance thermally enhanced window systems isn’t simply about comfort – it’s about long-term value, reduced energy bills and future-proofing against increasingly stringent environmental standards.

Both the T60 and W20 TE ranges represent over a century of steel window expertise, engineered for contemporary performance requirements without sacrificing the distinctive character that defines Crittall design.

Ready to specify thermally enhanced steel windows for your project? Our expert team can help you navigate technical requirements, U-value calculations and system selection.

Contact us today to discuss your specific needs and discover how our thermally enhanced systems can transform your vision into reality.