Importance of window U-Value

clint_eastman

I'll probably get annihilated for asking this but, how important is the window u-value?

My walls are 0.15 and I'm looking at 2 types of window. Triple glazed uPVC casement windows with a u-value of 0.8 (€18,000) or double glazed uPVC sliding sash with a u-value of 1.6 (€27,000), these have a wood grain finish.

Is it a straightforward choice? i.e. cheaper and better performing option over the better looking more expensive option.

Jimbo

It's all down to personal preference at the end of the day.
A uvalue of 1.6 is fairly standard spec for a window, but if your going to the cost of insulating your walls to a u value of 0.15, it dosent make sense to install standard spec windows especially if you can get windows with half the u vaule for 9k less.

Do you have large glazed areas in the house?

clint_eastman

Yeah, Thanks. I think I knew this but needed to be told as well!
I have a couple of large fixed glazed areas facing east and west.

Smcgie

Your BER assessor (whom you will need anyway) should be able to identify the difference in the energy usage between the two windows and identify what effect each window will have on your BER

sydthebeat

clint_eastman wrote: »

I'll probably get annihilated for asking this but, how important is the window u-value?

My walls are 0.15 and I'm looking at 2 types of window. Triple glazed uPVC casement windows with a u-value of 0.8 (€18,000) or double glazed uPVC sliding sash with a u-value of 1.6 (€27,000), these have a wood grain finish.

Is it a straightforward choice? i.e. cheaper and better performing option over the better looking more expensive option.

firstly, i wouldnt personally go for upvc with a sliding sash... they never were designed for such movements. Hardwood timber only should be considered for sliding sash..... for aesthetic and historical reasons.

secondly, 1.6 is pretty poor for a double glazed window these days. The standard would be 1.4, 1.2 is easily achievable.

when choosing windows always request the certifications. other posters can fill you in better on the intricacies of some of them, but basically, ireland has a WEP certificate which is a guarantee of performance.

Airtightness of a window is very important. When tested in accordance with EN12207:2000.... make sure they get either a class 3 or 4 rating.... 4 being best... if windows are not tested in accordance with EN 12207... walk.

sinnerboy

Apart from the calculated whole building energy demand resulting from 2G vs 3G - your sensible thermal comfort should be considered . By sensible I mean what your body can sense . The surface temperature of a 2G unit will feel a lot colder vs a 3G unit in a way that you can't really measure in BER rating or even your fuel bills . You will literally feel better with 3G in mid winter .

.

braftery

Hi there,

The U-Value of your walls is lower, therefore the heat in the space will move toward the easiest exit, ie the window. The lower the U-Value the better for windows.

However, every purchase in your home is a compromise between design, performance and budget. Unless you have an unlimited budget you will always have to make compromises.

Sash Windows in any material are not as effecient and are normally considerably more expensive, than other windows. This is a result of the design and complexity of construction.

A window with a lower U-Value will reduce your heating bills year on year so the additional money you pay now for triple glazing (approx 5%) will be more than re-paid to you in a short number of years.

Ultimately I think you are not really comparing to similiar products.

Do you want Sash windows ? If so then the other quote is just teasing you ?

If you are open to other types of windows then it seems a simple choice, buy the more cost effective and better performing window.

MicktheMan

sinnerboy wrote: »

Apart from the calculated whole building energy demand resulting from 2G vs 3G - your sensible thermal comfort should be considered . By sensible I mean what your body can sense . The surface temperature of a 2G unit will feel a lot colder vs a 3G unit in a way that you can't really measure in BER rating or even your fuel bills . You will literally feel better with 3G in mid winter .

.

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