How much energy do your double glazed windows and doors save?

28th March 2016

white PVC-U double glazing Very little heat passing through this beauty!

Craig Smith, Director at Copperfield Windows, gives a guide to energy efficiency when buying windows, doors and conservatories.

Energy efficiency and the desire to cut the cost of heating their home, is the main reason why most of us embark on the window and door replacement journey.  

Energy efficient PVC-U windows and doors are measured by what?

There are two systems for rating the performance of windows and doors – U-values and Window Energy Ratings (WERs). U-Values assess a product on how effective it is at keeping heat in or how much heat is lost through it, as a single measure of performance.

Window Energy Ratings do the same and use the U-Value (heat loss) but also balance heat loss against solar gain (warmth which passes into the room from the sun) and also throw into the mix additional heat loss through air penetration, giving windows a ranking from ‘A/A++’ to ‘G’ using a ‘traffic-light’ type colour code. The Door Energy Ratings Scheme replicates the same model.

What levels of energy saving do replacement windows need to meet?

To meet building regulations, all new windows must achieve a minimum WER ‘C’ rating or U-value of 1.6 or less.

The science behind double and triple glazed windows

Glass is the critical element in energy efficient windows. They work using two sheets of glass in the case of double and three, for triple-glazed units with a gap in between - usually about 16mm - to create an insulating barrier that keeps heat in. Performance is further enhanced using warm-edge spacers, low emissivity gases, for example, argon, xenon or krypton to fill the gap and low-iron glass.

Benefitting from energy efficient UPV-C windows and UPV-C doors and Composite Doors?

According to the Energy Saving Trust, fitting new energy efficient double-glazed PVC windows and doors, in a detached three bedroom home, can deliver an annual saving over and above single glazed windows of up to £160 a year in heating bills.

Other benefits of new energy efficient and low maintenance PVC-U windows and doors

Help to reduce condensation, while high security window and door multi-point locking mechanisms, also make homes far more secure.

What sort of thermal performance do I require?

Copperfield Windows supplies a thermally efficient triple-glazed window with a U-value as low as 0.8W/m².K. However, double glazed windows are more than adequate with a U-Value rating of 1.4W/m2.K.

We work with our customers to model heat loss and to develop a solution that’s right for their individual requirements and the build of their property.

For more information, please don’t hesitate to email me on or call a member of our team on 02476 452688.


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