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By now most people have become familiar with the energy-rating certificates shown on household white goods such as fridges and washing machines. These stickers show the rating of the appliance on a scale of 'A' to 'G'. The closer to an 'A'-rating an appliance is, the less energy it consumes to perform it's function. The less energy used, the less CO2 released into the atmosphere and the more money saved by the owner.

Now the same rating system can be applied to replacement windows and these ratings are supplied by the British Fenestration Rating Council (BFRC). Such ratings apply to the entire window, not just the glass installed in the window. 

We provide A-Rated windows as standard.

The overall energy index determines where the windows sits on the A-G scale and is calculated by taking into account:
Solar Factor - the amount of heat passing inside through the window from the sun
U Value - The amount of heat passing from inside through the window outside
Air Infiltration Factor - The amount of heat lost through air leakage through and around the window

The unit of the energy-index is energy transfer through the window (kilowatt-hours) per unit area (meters-squared) per year - kWh/m2/year. A negative number means overall heat energy is lost through the window, while a positive number means more energy is retained from the sun than is lost through thermal transmittance. The original A-rating was achieved at zero kWh/m2/year but as performance as increased, A+, A++ and A+++ ratings can be attained.

How Efficient Are Energy Efficient Windows?
The energy index rating cannot on it's own determine how much energy, and therefore money, that the window can save - it is a comparative figure that allows competing window products to be measured relative to each other.
In a typical house, the most heat loss will occur through the windows as these are the thinnest boundaries of the property. It makes sense therefore to focus energy-saving efforts here first.
Replacement windows are available in a range of energy-ratings and as you'd expect, an 'A'-rated window will perform better than a 'B'-rated window, and so on.
'A'-Rated Windows have a positive energy-index number - this means that more heat passes in from the outside than is allowed to escape outside through the window.
How Much Do Energy Efficient Windows Cost?
The higher the energy index of a window, the more production cost is involved in achieving that index and the higher the price will be. To determine whether energy-efficient windows are also cost-efficient windows, the customer must take into account:
- The number and size of windows in their property - the larger the area occupied by windows, the more potential there is for heat-loss
- The efficiency of their current windows - the biggest improvements will come from replacing single-glazed windows or windows installed prior to April 2002
-The pay-back period - Energy-efficient windows cost more up-front, but offer savings over the longer term.
As a guide, the BFRC suggests that an electrically-heated semi-detached house would save £461 (at December 2007 prices) per year by replacing single-glazing with 'A'-rated energy-efficient windows. It is worth noting that when it comes to selling a property, energy-efficient windows will improve the overall property energy rating and so increase it's saleability.
Do I Have To Have Energy-Efficient Windows?
No! At the moment having an energy-efficiency rating on windows is down to the manufacturer and completely voluntary. Windows that do not have energy-efficiency ratings have not failed any test, it simply means the manufacturer has not opted to have the windows tested.

Making contact with Paragon Windows

If you would like any more information about our products, you can call us on 01993 868791, email us at enquiry@paragonwindows.co.uk or use the form opposite. We also have a Facebook page!

If you request a quote, it's hassle-free: we will make an appointment to measure up and answer any queries, and then we email or post a fully detailed, itemised quotation within a few days.


Customer feedback from the Trading Standards Approved Buy With Confidence scheme


From initial contact and quote to complete installation - a great company. Competitive price, professional advice, reliable, pleasant and great installers.




Excellent service from start to finish


I was very pleased with the service and products I received from Paragon Windows and would be very happy to recommend them to friends & family.


This is the fourth house that Paragon have replaced the windows for us. The quality and workmanship is excellent.


Smooth process, high standard of workmanship, friendly fitters.


At Paragon Windows, our team of friendly windows and doors experts are committed to delivering every job on time and on budget. We rely on our customer’s feedback to build our reputation and are proud to serve our community in Oxfordshire. We hold a range of independent industry accreditations and are members of several professional bodies, customer feedback and quality assessment schemes, including Buy with Confidence, the Royal Institute of Chartered Surveyors, and FENSA.

Buy with Confidence

Trading Standards Approved directory of vetted traders with customer feedback. Learn more...

Royal Institution of Chartered Surveyors

Qualified fenestration surveyor for over 20 years. Learn more...


FENSA Membership allows us to register installations with Building Control without having to arrange inspections - FENSA carry out their own random assessments. Learn more...

Glass and Glazing Federation

We are members of the Glass and Glazing Federation. Learn more...

Privacy notice: We never send unsolicited marketing communications. Customer details are retained for a maximum of 10 years for the purposes of administering warranties, and only shared with: FENSA, for the purposes of registering installations with Building Control; our insured warranty provider, for the supply of any purchased policy.
Paragon Windows, Bay 6, Crawley Mill Industrial Estate, Crawley, Witney, OX29 9TJ
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