What U-Value should I look for in windows?

S

SillyMonkey

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Worked out roughly that the U-Value of my walls will be 0.21. So far have got 2 quotes for windows. The expensive ones have a U-Value of 1.1 and the cheap ones have "B rated" U-Value (need to clarify with him what excatly that is).

Just want to know if the 1.1 is overkill, I have no idea what the windows should be since there is no way it's going to be anyway near 0.21.

If 1.1 is not the required value, what would be to match the walls (if you know what I mean)

BTW i'm not going for any particular rating, just trying to do the very best I can for what money I have. Trying to get the best insulation in the house first any worry about everything else later.
 
Just looking at the Kingspan guide:
0.21 for your walls is between A3 and B1 rating.
For A3 they recommend 1.3 for your windows, and for a B1 1.5.

This will depend on the particulars of your design - do you have lots of glazing, small windows to the north etc.

Generally it is not economical to put in an A1 rated window in a C rated house for example.

Consider having better rated windows to the north elevation as a compromise.

What rating do you wish to achieve with your construction? What is the difference in price between the two prices for windows? When fed into your DEAP calculation, what effect does the difference make? With the price difference, can you achieve a better energy saving by spending the money on another area of your house (preferably on insulation, as technology can be easily added later if you wished)?
 
You need to be careful with companies giving U-values, as there are different U-values for the glass and for the whole window including the glass. It is the U-value for the whole unit, frame glass etc that you require. Many companies quote the U-value for the glass alone and that is not a proper U-value. U-values will also be different for each individual window as a larger window will get a poorer U-value than a smaller sized window. Timber windows are also inclined to get slightly poorer U-values than their U-pvc counterparts for the same sized window. If you are getting U-values of the full window within the range of 1.3 to 1.5 that is quite good values.
Hope this information helps
 
I was of the opinion that timber windows (especially hardwood) would have a better u-value as they are a solid frame (thus insulated fully through) as uPVC have a hollow centre with a steel square section in the middle (i am aware that some newer types of uPVC have insulation also in the centre). I stand to be corrected.
 
Secionn is absolutely right. Be inquisitive with companies when they quote U-values... what are they actually quoting... 1.1 will almost certainly be the glass alone (low-e, argon filled double glazing). 'B' rated windows will have a certified (and tested rather than simply calculated) U-value of around 1.45.

I would recommend looking at rated windows as opposed to those with quoted U-values as these will be certified. This certificate will allow your house to be accurately rated when assessed for energy efficiency. If you do not have rated windows the assessor will simply apply a nominal value to your house which may affect its overall rating and therefore value (or at least speed of sale) if and when you come to sell up.

Also, be careful when mixing and matching different ratings / qualities of window in different parts of the house. First, the performance of a window is not affected by its aspect. While some glass types do allow more of the sun’s heat radiation through, generally window performance is based on the amount of heat lost through the unit and so does not take account of incoming energy. Second, some manufacturers use different glass types to achieve different levels of performance for heat retention. This can sometimes be quite noticeable from the outside of the house.

For more information check out the British Fenestration Rating Council website
http://www.bfrc.org/
 
It should be known that the declared elemental u value of the window HAS TO BE certified for it to be included in any Building Energy Rating (BER). Even if the manufacturer swears by a u vlaue, if its not certified the default worst value has to be included in any BER. This is vitally important in determining which window you will purchase.

What you want to be purchasing is double glazed windows with thermally broken frames, low e glass with soft coat of 0.05..... (not hard coat). The wider the gap between panes the better. Anything over 16mm is good.
 
Hi SillyMonkey,

Just completing my house build and from my experience the 1.1 U vaue you are quoting is the Centre of glass value generally toted about bu most manufacturers.

My advice is to shop around as most suppliers now offer the latest double and triple glazed options, and make a comparison table of all the 'quoted' statistics. Check values and quoted dimensions as in my experience some 'fibs' are often told.

Be sure to get the total window U value but also look at the heat gain co-efficients and air tightness of the units. A window with a low U value is worthless if it is poorly constructed!

Best of luck

Reuben
 
i was told by a window sales girl, that their A rated window was 1.4 of a U Value and B rated was 1.7- these figures seem higher than suggested above?
 
bamboozle said:
i was told by a window sales girl, that their A rated window was 1.4 of a U Value and B rated was 1.7- these figures seem higher than suggested above?
Click to expand...


with u values.. the lower the figure the better the performance.

a figure around 1.3 for double glazed would be a good u value.
 
bamboozle said:
i was told by a window sales girl, that their A rated window was 1.4 of a U Value and B rated was 1.7- these figures seem higher than suggested above?
Click to expand...

Generally A rated are about 1.3, B rated are about 1.4 and C rated are about 1.5.

This is very much a rule of thumb though so be sure to ask for actual figures for the units you are purchasing.
 
I've recently had lads out from 2 of the more reputable window companies as suggested on AAM and both of them said their windows have u-values of 1.1 as standard and called them B energy rated, but they were referring to the glass rather than also incorporating the frame.
 
Just to update everyone a little, there was an excellent seminar in the Red Cow Moran Hotel last Thursday organised by Promac Group with guest speakers, Simon Coveney FG spokesperson for Communications, Energy and Natural Resources, Andy McDowell from Pilkington Glass, Barry Smith from National Standards Authority, Giles Wilson from BFRC, Kevin O'Rourke from SEI, and Andy Jones from Edgetech.

It was great to have everyone agreeing that Ireland needs to have standard regulations introduced such as electrical products, ie the A,B,C in the colour coded graph and also an "Energy Recommended" label. What the consumer needs to be looking for is a WER (window energy rating) which applies to the whole window as a unit not just the glass.

A BER applies to the whole house not just the windows and doors. When a BER Assessor is assessing a house and does not know the rating for a window a default setting of 2.2 is used. Also consumers need to be looking at the idea of Solar Gain from windows and doors when making their choices.

A poster above mentioned that the wider the spacer bar the better - Andrew Jones from Edgetech mentioned that 14.7 in actually optimal for spacer bars.

I look forward to the follow-up seminar when the above bodies have agreed as to what is going to be the standard for Ireland, which will eliminate the current guesswork when making such an important investment for ones home.
 
Hi NHG. I was wondering the same thing.Did anything ever come of this or do we still have to rely on window suppliers being good for their word or having their windows voluntary tested by BRFC in the UK?
 
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