U value on windows

radar01

Hi

I have been given two quotes for new windows in a new 4 bedroom detached house we are having built. One for double glazed and one for triple glazed. Window total size covers 23m2. The triple glazed windows are £850 more than the double glazed. Both are Kommerling and guaranteed for 10 years.

Double glazed
U value 1.54
Label Index = -5
Window Rating = B

Triple glazed
U value 1.11
Label Index = +7
Window Rating = A

So my question is would it be worth going for triple glazed? Would I save money in the long run and when would I start seeing a return? The floor U value will be 0.13 and so will the roof.

Any help will be much appreciated.

anotherbaldrick

You will probably not save much money, guess £40-50 per year. You will achieve more energy saving by concentrating on the thermal efficiency of your roof , walls , floors and controlled ventilation and air-tightness. But what triple glazing will give you is better comfort conditions, with large panes double glazing will still give some cold air circulation from the inner pane, tripple glazing cures this.

Triple glazed PassivHaus windows and thermal comfort

The radiant interior surface temperatures play an important role in how humans perceive thermal comfort. Radiant temperature asymmetry is key i.e. surface temperatures must be close together. If a surface temperature difference exceeds 4 °C we notice it, we can feel it. So if we take a comfortable internal air temperature, in a Passive House or good standard Low Energy house, of 20 °C we can expect to find that the inner surfaces of the external walls to be at around 19 °C and the surfaces of internal partitions to be at around 21 °C.
The internal surface temperatures of double glazing vs triple glazing will be quite different.

MX5huggy

It will be no where near £50 saving per year. Payback of under 10years, it will more like 40 years.

Give the u- values to your SAP assessor they will be able to tell you the diffrence it makes to the yearly cost and fabric energy efficiency.

Ideally you would also give them the 2 g-values as well, this is the solar gain number because the solar gain is lower with triple glazing you may find it calculates that DG is better. You could try TG on the north and DG on the south elevations.

Having said all that, it not just about pay back and value for money, because if it was you would just build to the minimum u-values and put a big PV Array on the roof. For £850 I would go TG.

anotherbaldrick

MX5huggy wrote: »

It will be no where near £50 saving per year. Payback of under 10years, it will more like 40 years.

Give the u- values to your SAP assessor they will be able to tell you the diffrence it makes to the yearly cost and fabric energy efficiency.

Ideally you would also give them the 2 g-values as well, this is the solar gain number because the solar gain is lower with triple glazing you may find it calculates that DG is better. You could try TG on the north and DG on the south elevations.

Having said all that, it not just about pay back and value for money, because if it was you would just build to the minimum u-values and put a big PV Array on the roof. For £850 I would go TG.

You totally missed the point I made, the benefit of triple glazing is that the temperature of the inside glass is up to 2deg C more than with double glazing and this gives a much better comfort condition and less cool air circulation down the face of the windows. far more important than any money saving gain.

The physics involved here have been worked out in Germany by the PassivHaus Institute. It has shown what happens to surface temp­eratures on various forms of glazing when it gets really cold outside, and the internal air temperature is designed to be at 21°C:

• Next to a single-glazed window, the internal surface temperature is around 1°C.
• Next to a double-glazed window (2000 vintage), the surface temperature is around 11°C.
• Next to a modern, energy-efficient double-glazed window, the surface temperature is 16°C.
• Next to a triple-glazed window, with a centre-pane U-value of just 0.65, the temperature is 18°C.

But a point often ignored is that there are savings in using triple glazing. As there is considerably less cool air convection from the inside of triple glazing comfort conditions can be achieved at a lower overall room temperature (probably 2 deg) so the thermostat can be turned down from 23 to 21.

MX5huggy

I don't miss the point at all, your 1st sentence says there will be a saving of £40 to £50 per year. Without plugging the whole house into SAP or passivhaus I can't work it out correctly, but I know the windows will be replaced before you get a payback on the £850.

Yes top notch TG does all you say, but we are not talking about a center pane of 0.65 we talking fairly ordinary DG vs fairly poor TG.

anotherbaldrick

MX5huggy wrote: »

I don't miss the point at all, your 1st sentence says there will be a saving of £40 to £50 per year. Without plugging the whole house into SAP or passivhaus I can't work it out correctly, but I know the windows will be replaced before you get a payback on the £850.

Yes top notch TG does all you say, but we are not talking about a center pane of 0.65 we talking fairly ordinary DG vs fairly poor TG.

Youre still not with it , the whole point of what I have said is that the main concern should be comfort conditions which triple will give over double . Also the warmer glass will allow you to achieve comfort at a lower system temperature ( Cost in that saving ) Your tone would lead one to believe you have a poor opinion of Kommerling ?

radar01

Thanks for your replies. So you think triple glazed is still worth going for but not for money reasons?

As the walls U - value will be 0.27, floor 0.13 and roof 0.13 I thought the only other place I could save money would be on the windows but not sure if it would be worth it if you think the max I could get is £50 per year.

The G value for the double glazed is: 0.46 and the 0.38 for the triple glazed.

The double glazed is quoted at £10K + VAT installed. Is that a good price?
4 bedroom windows 180cm x 130cm

3 kitchen windows 100 x 110

patio doors with side panels 300 x 220

3 bathroom window 75 x 110

2 back doors

1 front door

bay window
250cm x 150cm
80cm x 150cm
80cm x 150cm

missprice

To help OP.

I have TG windows in whole house. they had to be done at different times as I didn’t have the money for them all in one go, so
downstairs three windows one massive and 2 large. they have wood frames with aluminium cladding, mega expensive at
£1800 for the 3.
upstairs I have 5 windows. I massive 1 large and 3 small (one of the three small is fixed) and cost last Dec was £1637. they are simply Upvc frames.
the difference in heat is also massive as I only have heating downstairs. so upstairs through this last winter it has been cool rather than so cold you could see your breath.:rotfl:
I did the TG for reasons of sound (noisy neighbours from hell) but the difference it has made in heating as well was worth it, and for a bit more info the best DG quote for the upstairs was only a £250 difference between DG and TG



umm if I can I will dig out the sizes if you really need it.???????

edit to add the prices quoted inc VAT and fitting but not making good the plaster where it came off in lumps due to straps being used for previous windows

radar01

Hi Missprice and thanks for the info. Do you know what u values the windows were? What make are they?

missprice

radar01 wrote: »

Hi Missprice and thanks for the info. Do you know what u values the windows were? What make are they?

can tell you the downstairs wood framed are u0.9 cant tell you the make as they were made by the same co that fitted them which was based in Manchester, and I was so desperate to get them I didn’t care who made em

upstairs were made by a different co (in Leeds) and I never visited to see how they were made and cant remember co name sorry but they more usually make DG. oh and u1.1 I think the difference is due to Upvc frame rather than wood but I could be wrong

got sizes now if you want?

largest 2000 x 1200 there’s one each up and downstairs

next largest 900 x 1200 2 of these as well 1 up 1 down
then 500 x 1200
1100 x 600
fixed 500 x 600


hth

radar01

Am I paying too much then? It's 10k plus vat for double glazing 1.5 kommering.