Understanding Window Energy Ratings

Photo of author

Nick Dardalis

Updated on

If you installed double glazing 20 or more years ago it is quite likely simple weather protection, draught-proofing and the replacement of existing windows were the main reasons for your purchase.

Early window systems were simple products designed to accept two pieces of glass with what today would be classed as marginal increases in security and performance. However, the introduction of Window Energy Ratings has lead to significant improvements.

early double glazing was about simply improving on a single piece of glass rather than energy ratings.
Early double glazing was about improving on a single piece of glass rather than energy ratings.

Early double glazing was there to provide an instant improvement to our homes with the benefits that two pieces of glass brought over one.  The double glazed units of early replacement windows and doors was simply a sealed unit with air space in between.

The thermal performance of frames did not come into consideration. Indeed, early pvcu or aluminium window frames were non-insulated standard sections. Double glazing is believed to have originated in the 1930’s in America but took nearly 40 years to reach the UK and become a standard for window replacements.

How did early double glazing perform compared to today?

U Values and Solar gain were not a consideration for early variants of double glazed windows. Whilst single glazed windows were capable of drawing in warmth from the sun, the one piece of glass couldn’t retain the heat coming in.  Therefore the addition of the extra pane of glass made a noticeable improvement with the benefits instantly felt.

The early nineties saw the addition of thermally broken aluminium windows as well as improvements in double glazing technology.  U Values and Window Energy Ratings were performance figures that the public was still not aware of.  Window systems were designed around aesthetics before performance.  Today this is the reverse – windows are designed around performance with aesthetics still playing an important part but arguably as a secondary consideration. The U Values of early windows and doors are calculated at approximately 5.9Wm2K for single glazed windows, 2.9Wm2K for double glazed windows.  This is a huge difference from modern windows and those designed to meet passivhaus standard which are well below 1.0Wm2K.  The difference between modern and original double glazed windows is clear to see.

What do we expect from modern double glazed windows?

polyamide has been used for many years already and is a nylon that contributes greatly to well insulated aluminium windows.
Polyamide has been used for many years already and is a nylon that contributes greatly to well insulated aluminium windows.

Irrespective of material, double glazing is required to be attractive, secure, weather resistant and energy efficient.  It is Building Regulations that now dictate the energy efficiency of current and future windows and phrases such as “will meet and exceed current and future Building Regulations” is well used by many designers and producers of aluminium, PVCu and timber doors and windows. We expect our windows to keep even more of our heat in and play their part in reducing heat loss from the home and ultimately reducing energy bills.

Triple Glazing is the latest trend to hit the UK home improvement market although this has been in use in Europe and colder countries for many years already.  An A, B or C rated window is acceptable as meeting current building regulations but window designers today are embracing modern materials such as polyamide, polyurethane, argon gas, warm edge spacers, low emissivity coatings to work together in giving us greater energy efficient windows and doors.

What is a window energy rating?

energy ratings are classified from a to g, with a rated being the best performing.
Energy ratings are classified from A to G, with A Rated being the best performing.

If you are looking at new windows or doors how important are the window energy ratings to you?
With many window companies now advertising an A+12 or more, do the differences between A, B or C rated windows matter? Window energy ratings now vary from A right down to G and explained with the energy rating labels that we are used to on home appliances as well as windows.  Energy ratings are also used for Energy Performance Certificates (EPC’s) for homes whether bought or rented.
To arrive at the Window Energy Rating the following Values all come into consideration.

The Energy Index

The Energy Index is used as an indicator for the heat or energy gained as well as expelled through any window.

The U Value

The U Value is thermal transmittance.  This is where the all-important glass comes in.  The high specification the glass, the lower the U Value.

The G Value

G Value is the solar gain/loss through windows.  The higher the G Value, the more solar gain through a window.

The L Value

The L Value relates to leakage of air through a window and with any well designed, well sealed and weather resistant window this figure must be zero.

Should Window Energy Ratings matter to you?

Ultimately it is up to you to determine how the varying U Values of all the different types of windows will affect the energy conserved and used.  An experienced window professional will not simply say “our windows have the best energy rating” but will be able to accurately tell you how these different ratings matter.

However, B and C rated windows should not be discounted in favour of an A-rated window in every case. We must also remember that the purchase of new windows and doors is an “emotional” experience, so customers must find windows and doors attractive to them and right for their home even if their energy ratings may be less than those advertising the highest possible ratings.

Some Clarification on A Ratings

by Nick Dardalis

cab logo
The Council for Aluminium in building promotes and supports aluminium for our industry

There is an excellent article from the Council for Aluminium in Building explaining the differences between the BFRC and the BRE Green Guide ratings.

The Council For Aluminium in Building(CAB) is a really good organisation with memberships from across the industry.

In this guide the CAB explain that there are presently three different schemes that mention ‘A’ ratings. They say:

Right now we have three schemes that contain references to ‘A’ ratings and which form part of most tender specifications. They are:

British Fenestration Rating Council (BFRC) – Window Energy Rating (WER) scheme with Bands A to E: www.bfrc.org

BRE Green Guide (GG) to specification – Environmental profiling system for building materials and components with Bands A+ to E: www.thegreenguide.org.uk

BRE Environmental Assessment Method (BREEAM) – a range of products that use GG ratings as part of their building credits system: www.breeam.org/index.jsp

The CAB make an excellent point in obtaining clarity when you are asked to supply an A rated product.

Providing expert help to homeowners and trade professionals since 2010

expert

Free

Impartial

Get Free help finding the right products from the best suppliers

Andrew DOBSONAndrew DOBSON
16:42 30 Oct 23
Nick responded incredibly quickly to my enquiry (on a Saturday too!), and was able to offer invaluable advice on both aluminum systems and manufacturer / suppliers. Thanks Nick!
chris steerchris steer
16:18 09 Oct 23
Had a meeting with Nick during the grand designs show. Was extremely helpful and professional would highly recommend
Chris WesthorpChris Westhorp
19:55 13 Sep 23
Extremely helpful with pointing us in the right direction to find the products we required and suggesting firms that could reliably fit them.Nick was quick to reply and very detailed in his advice.Highly recommend reaching out to them.
Cathy GreenwoodCathy Greenwood
07:03 11 Sep 23
Update - A second email to nick for help on bifolds resulted in a detailed informative reply even on a Sunday ! This guy is so knowledgable and helpful .I approached Nick for an independent view on sliding doors v bifold and the different brand options . His reply was extremely detailed and prompt and allowed me to navigate this often confusing world in a much more informed way . Thanks so much Nick
Anthony CraigAnthony Craig
12:45 05 Sep 23
This is a must site for anyone looking for advice. Great service and very quick answers to questions. Nick has been of great help quiding us through the maze of aluminium products. Thank you
Philip DuffieldPhilip Duffield
20:24 26 Jul 23
I contacted Nick @ ATS for guidance on what aluminium sliding door systems would be suitable for an opening in an extension that is going to be both wide and tall. He came back really quickly with very detailed and incredibly helpful advice. He is clearly extremely knowledgeable about the systems on the market and their respective features and capabilities. If you’re feeling a bit lost by the overwhelming range of choices out there, I’d definitely recommend contacting him.
Dariush HekmatDariush Hekmat
17:25 19 Jul 23
Nick's advice is great. He is always quick to respond and spends time on responses, which really help to make an informed decision.
Alan FosterAlan Foster
07:51 12 Jul 23
Absolutely fantastic. Asked for advice about replacing Crittall (?) windows late last night and early this morning received 3 great suggestions and contact information for suppliers
Rachel LauRachel Lau
09:24 16 Jun 23
Fantastic website full of valuable and pragmatic advice about product selection and comparison: no other website gives information like this. Truly written for public interest. Don't hesistate to reach out to Nick via the mailing system. He responds very quickly, is friendly, and has very sound and high knowledgable advice. I have already shared this with my friend planning her own grand design.
guard Charlieguard Charlie
12:28 14 May 23
I emailed this company just on the off chance they could help me with new magnetic sliders for my patio door. They were not able to supply those but were so very helpful providing me with the name of a company who could. I am so very grateful at the great service. Dare say customers must be very happy. thank you so much.
Benjamin LewisBenjamin Lewis
10:06 04 May 23
Nick is very helpful indeed. Extremely knowledgeable on bifolds which was in relation to my query. Great website as well, some very useful articles. Particularly appreciated the article that lists all the major bifold options in order of their sightlines! Thank you!
P JonesP Jones
08:07 15 Apr 23
I asked Nick some questions about an installation we were considering and he replied within hours with some very useful suggestions that will probably lead us to using a different make and supplier. Thanks, Nick. Great work.
Nicholas WallNicholas Wall
13:18 02 Apr 23
Looking for fair and honest expert advice on all aspect of aluminium windows and doors? These guys will arm you with all the information you need to make the RIGHT choice in a highly complex, crowded marketplace. post a question and you will get a very quick professional answer you can rely on being based on fact. Thanks guys!
Giorgia SiriacoGiorgia Siriaco
16:25 21 Mar 23
After a lot of research to find doors that would meet our unusual size requirements and feeling increasingly uncertain about the best way to spend our small budget, I stumbled on the ATS website, and I'm so glad I did! I contacted ATS to request advice and Nick promptly replied with a wealth of information, providing us with options and relevant contact details. I only wish I'd found them sooner!
Carol NortonCarol Norton
10:01 17 Mar 23
I've been so confused about how to achieve the look I'm after, and going round in circles with various window/door companies, trying to get away from the huge chunks of plastic currently around my windows. I didn't expect an email to a company found through a Google search to really help - but I was desperate, so I tried. I'm SO glad I did. Finally I have clear explanations from ATS of where I've been going wrong, exactly what I'm looking for, and a list of local companies that might be able to provide it! The response has excelled my expectations and I feel as if I'm finally inching closer to a home with which I'll be happy and comfortable: thank you.
David NunnDavid Nunn
20:54 14 Mar 23
It is rare that I write reviews, however after my very positive communication with Nick - enquiring about suitable slim sash aluminium windows for my project, I felt that a review was definitely warranted. I can reinforce the many positive reviews posted so far, Nick was very quick to respond, providing comprehensive detail, with excellent independent advice.In summary, great service, thank you Nick.
Chantal AuerbachChantal Auerbach
13:04 09 Mar 23
Nick from Aluminium Trade Supply was incredibly helpful informative and pleasant to deal with. He responded quickly to emails and was very knowledgeable. Highly recommend being in touch with Nick if you are considering new aluminium windows or doors.
Lee JonesLee Jones
20:21 22 Feb 23
I dropped Nick at Aluminium Trade Supply an email re high security slim sightline bi-folds and their alternatives and he responded that quickly (and so comprehensively) that I felt bad I’d not paid him for his time!Nick Sir your product knowledge is outstanding and you are providing a level of service that goes wayyyy above and beyond expectations. I’ll definitely make sure I mention Aluminium Trade Supply to anyone I encounter looking for a fenestration solution 🙏🏼
G JG J
15:13 13 Feb 23
We are looking to replace some old UPVC patios doors with aluminium ones. The ATS website is a great source of advice in an area where clear information is sorely lacking. Having used the website, I then followed this up with a number of specific questions relating to our search, and Nick came back very quickly with clear, detailed and very useful advice.I have been very impressed with both the website and with Nick's advice. My only regret is that I didn't come across ATS before replacing various windows in 2021 - I'm sure it would have saved me a lot of grief and money! Thanks again Nick.
Azza McCabeAzza McCabe
17:47 01 Feb 23
So impressed with this company.Responded to my query quickly andgave valuable advice. Nick was extremely helpful and we were able to move forward with our project.
Adri LoloçiAdri Loloçi
11:21 08 Jan 23
Nick was super fast to respond and provided some great recommendations. I would recommend this website to anyone looking to find bifold or sliding aluminium doors.
Stephen HoustonStephen Houston
16:16 03 Jan 23
Looking for aluminium crittall style internal door and external patio French doors. Noted good reviews and thought would ask for advice. Comprehensive reply with excellent independent advice and lists of fitters who could provide products and installation. Great service.
Inga GeachInga Geach
08:25 21 Dec 22
Nick from Aluminium Trade Supply has been extremely helpful with navigating the jungle that is aluminium glazing for our upcoming extension project. His advice was prompt, detailed and always impartial. Very grateful for your input, thanks Nick!
Amanda BurtonAmanda Burton
10:54 16 Dec 22
Brilliant website and an excellent service. Nick provided not only detailed advice and supplier contacts, but highlighted the considerations of various products so I could make an informed choice. Our Sunvista minimal sliders were fitted this week and I couldn't be happier, stunning. Thanks once again for your advice and recommendations, invaluable!
Keith BarnesKeith Barnes
17:18 10 Dec 22
Very helpful advice given to my question, including the name of 3 different companies that i could try for the product being enquired about. Many thanks
Munim ChowdhuryMunim Chowdhury
11:45 13 Sep 22
Nick has been very helpful on signposting me to a number of partner organisations for steel/aluminium doors.
SUSAN wallaceSUSAN wallace
17:26 31 Aug 22
My experience with this firm was exceptionally good and this is notalways the case as a female, dipping a toe into technical waters.I was spoken too with courtesy and at a level that helped me consolidate what was needed .On top of that I was given a list of companies and places where I could obtain the type of product I needed.I could not thank them enough and would certainly go there again and reccommend others do too.
Paul SalterPaul Salter
22:39 22 Aug 22
Contacting Aluminium Trade Supply is like contacting the Oracle direct. Advice is always comprehensive and balanced. On multiple occasions they have provided me with options that fully meet our objectives. Many thanks.
Nick McCormackNick McCormack
20:25 14 Aug 22
Really helpful and useful came back to me on a Sunday with some invaluable information. Highly recommended.
ray addisonray addison
13:14 14 Aug 22
received a prompt reply to my query,and helpful information from ATS
js_loader