Rules governing the performance of windows changed in October 2010. Before then windows had to have a U value of 2 (1.8 in Scotland), as from 1st October 2010 the new u value is 1.6 for both England and Scotland, or a WER (Window Energy Ratings) that is C rated or better.
Any contract signed before that date can still have the old values until the end of March 2011, but any contract signed on or since October 1st 2010, must comply with the new regulations.
For years U values were the only measurement being used, but this dint account for energy gain, the free solar gain that naturally enters the building, and not just in the summer months, low sunshine during the spring and autumn mean that lots of solar gain is possible whilst it is still cold outside.
To calculate the heat being lost and the heat being gained is a bit complicated, that’s where Window Energy Ratings come in. Most companies who manufacture windows will by now have tested and results showing the values for their products, A,B,C or worse.
For years 5.8 was used as the u value measurement for single glazed windows, that’s 5.8 units of heat, being lost every hour, for each 1sq metre of glass, for every 1 degree difference in temperature, between the outside and inside)
So if it’s -8 outside and + 18 inside, that’s 150.8 units of heat EVERY hour through a pane that’s just 1metre square!
Standard, air filled “double glazed sealed units” 16, 20 or 24mm sealed units, meant that this figure could be reduced to approx 2.8, a significant reduction, so the new figure of 1.6 is a huge improvement and the government wants to see it reduced again in 2013 by a further 25% to 1.2.
Window Energy Ratings are issued by BFRC, the British Fenestration Ratings Council, they have issued the majority of Window Energy Ratings by licensing specific products, taking into account:
- The heat loss through the frame material
- The surface coatings on the glass to reflect or trap energy
- The air leakage between the moving opening parts of windows
- Even the amount of sunlight it can expect during the year!
For the record, EST the Energy Savings Trust, only recommends Energy Efficient products, those rated B or better, so they’re the only ones that can legally carry the blue Energy Savings Recommended swing tag logo. This is an important factor to look out for when looking at Window Energy Ratings.
1) It’s natural to say we will just have A rated then, its better than B or C, and that’s true, however to get to an A rated product some companies have to remove the steel reinforcing making energy efficient but weaker product.
2) Get the specification in writing, because some companies will show you the A rated product, but price for a cheaper one, make sure it says on the contract it’s a C rated product, and check for the permanent marking of the window frames when they arrive.
3) Use the verify button on our web site to check if the company really does have a license for the products they claim.
To find out more about Window Energy Ratings visit the following: