Dream | Design | Deliver

From thermal performance to weather durability and security, windows and doors can offer home owners many benefits. We’ve identified the key performance features that you should look out for to maximise your return on investment on window and door purchases.

How to keep the warmth in, and the draft out

The way that windows and doors are constructed and the materials used to build them greatly impact their thermal performance. 

Here’s how to maximise your solar power….

Opt for timber construction

Timber is a natural insulator and has a high thermal performance.

In comparison, PVC-U frames are “thermally broken”, which means a barrier is placed between the inside and outside of the frame to prevent conductive thermal loss. Timber frames don’t need this feature.

Glazing system

Choose glazed units that are filled with argon gas (which is a non-toxic, odourless gas that acts as an insulator) - as this offers a lower thermal conductivity than air.

“Low e-glass” windows and doors can improve the internal and external transfer of heat – which helps to create the optimum indoor temperature.


A “U-value” measures the energy performance of a complete window or door unit. It measures how well heat is transferred by the entire product – including the frame, sash and glass – either into or out of the building. And, the lower the U-Value number, the better the window or door will keep the heat inside a building.

FACT - All Rationel products have been given a U-Value number based on size and specification. You can find them on page 11 of each range’s brochure.

Double gasket/seals

A “double gasket” provides a tight seal between the sash and frame of a window or door unit, enhancing its air and water tightness, and helping to keep the heat in.

To discover how you can benefit from our help, simply get in touch by calling a member of our team on 01869 248181, or email generalenquiry@rationel.co.uk.


Alternatively, click here to download our brochure.