When choosing new doors or windows for your home or commercial property, one of the key terms you’ll come across is the U-value. At 23 Doors Limited, we’re passionate about helping our customers make informed choices, so let’s break down what U-values are and why they matter.
What Is a U-Value?
A U-value (also known as thermal transmittance) measures how effective a building material is at preventing heat from escaping. In simple terms, it tells you how well a window, door, or rooflight keeps warmth inside your building. The lower the U-value, the better the insulation.
U-values are expressed in W/m²K (Watts per square metre per degree Kelvin). This refers to how many watts of heat pass through one square metre of material for every degree of temperature difference between the inside and outside.
Why Are U-Values Important?
Energy efficiency is more important than ever—both for reducing heating bills and minimising environmental impact. A product with a low U-value helps:
- Keep your home warmer in winter
- Reduce energy usage
- Lower your carbon footprint
- Comply with UK building regulations
By understanding U-values, you can compare products and make sure you’re investing in energy-efficient doors and windows that offer long-term value.
What Affects a U-Value?
Several factors influence the U-value of a product:
- Frame material – Aluminium with a thermal break performs better than standard aluminium.
- Glazing – Double or triple glazing, gas-filled cavities, and low-emissivity coatings can significantly reduce U-values.
- Design – Slimmer frames with larger glazing areas can improve performance, especially when high-spec glass is used.
All these components work together to provide better insulation and comfort.
U-Values and Real-World Performance
While U-values are a great way to compare products on paper, real-world performance also depends on quality installation and correct fitting. Poorly installed windows or doors—no matter how low their U-value—can still result in drafts, cold spots, and heat loss. That’s why 23 Doors Limited not only supplies high-performance products but also works with trusted installers to ensure everything functions at its best.
U-values are a vital indicator of a product’s thermal efficiency. The lower the number, the better the insulation. Whether you’re upgrading a single door or building a new extension, choosing products with low U-values is a smart move for both your wallet and the planet.
At 23 Doors Limited, we offer a wide range of aluminium doors, windows, and rooflights designed to meet—and often exceed—modern energy performance standards. Get in touch with us today to find out more about our energy-efficient options and how they can transform your space.
