Menu Sign In Contact FAQ
Welcome to our forums

How much energy does it take to make a double glazed unit?

This is Hangar Talk so bear with me – there is no better group than Euro GA to work this out as we have the best people here

I am interested in the heading as I seem to have replaced about 30 double glazed units in the last 10 years which have failed due to going “cloudy” – the seals fail after about 20 years although south facing units seem to fare the worst. In one property I had to replace every south facing unit – 12 windows (24 units)

What interests me is how much energy did they save over the 20 years compared to (a) melting the glass (b) distribution (c) truck rolls to measure and replace (d) disposal of the old unit.

We used to do these sort of estimates in A level Physics but I’m a bit rusty! Any help or estimates welcome.

United Kingdom

“We used to do these sort of estimates in A level Physics but I’m a bit rusty! Any help or estimates welcome.”
Even at University Physics I never saw the hard data you would need for these calculations.
I think the whole “Green Energy” thing is a massive con in Scotland, and possibly in the UK.

EGPE, United Kingdom

Yes I agree, with PV panels, there is some Latitude where unsubsidised they don’t make economic sense. They only give a fraction of output under a cloudy sky.

I am interested in the same sort calculation for a double glazed window. I suppose there must be some sort of energy it takes to make 1 cu meter of glass. We know the energy saving value as it has a U value compared to a single glazed panel. Perhaps a single glazed panel saves money over it’s lifespan (which would be 100 years plus or 4-5 times the life of a double glazed unit?)

It would be tricky to work out but you can bet the BBC or any UK Newspaper /Economist will never do that calculation – it goes against their green religion

United Kingdom

What is a “double glazed unit”?


LeSving wrote:

What is a “double glazed unit”

I guess they’re talking about sealed double glass panes for windows.

ESKC (Uppsala/Sundbro), Sweden

A sealed double-glazed unit is a factory-produced window made to specific dimensions for installation in a new-build house or retro-fitting in an existing one.

As opposed to a traditional window, measured, cut and fitted on-site by a glazier.

This is where you tell me that the distinction seems odd because the latter have not been seen in Norway for fifty years!

The question is essentially, does refitting an older house with double glazing consume more energy than it saves?


According to this the manufacturing footprint is in the ballpark of 100kg / m^2 (Strongly depending on the frame material).

Therefore if you replace a 60ies single pane window (U up to 6 W/m^2K ) with a modern 3 pane Argon filled one (U as low as 0.5 W/m^2K) in a house with fossil fuel heating it should be carbon positive within the first year


Malibuflyer wrote:

with a modern 3 pane Argon filled one (U as low as 0.5 W/m^2K)

Are these common in Germany?

They aren’t in the UK and I’ve never seen one. I don’t know if present building regulations require them in new builds, but I doubt it.


Graham wrote:

Are these common in Germany?

They are getting more and more common: For new buildings the highest Energy Standards can only be met when you use them. When you renovate your house the price difference between the 2 and 3 pane windows is typically lower than the subsidies you receive when using 3 pane windows.


The tendency in the UK is to have very small windows in new builds because

  • they are cheaper to make
  • they lose less heat through the windows, so building efficiency compliance is easier to meet
  • in the countryside, the dickhead planners don’t like big windows due to “light pollution” (no use telling them there are c-u-r-t-a-i-n-s)
  • large windows aren’t “English vernacular” style

Of course anybody who wants a nice house will go for biggest possible windows, if the view outside is nice.

Triple glazing is very rare in the UK. It was quite common in Czechoslovakia when I lived there in the 1960s, and the three panes could be separated for cleaning.

Yes the problem with double glazed units “blowing” is notorious. It is caused by

  • poor assembly of the seal (most of these units are made by cowboys – the double glazing trade is notorious)
  • the use of cheap screws to fix the frames to the bricks/blocks; the screwheads rust, expand, and puncture the seal of the glazed unit
  • the use of window frames as structural supports for the ceiling
  • in UPVC windows, the use of steel frames, which rust and the expanding rust penetrates the double glazed unit

Practically every window job I’ve ever had done, including my first flat in 1983, was glazed by crooks and shysters. The last one had the lead tray stopping about 5cm short of the ends, so the water ran straight out into the wall So I now watch them like a hawk and free issue them with stainless steel screws and make sure they actually use them. They also need to make the unit sit on plastic spacers which support it a few mm above any screw heads. A friend of mine in Germany has recently built a super high tech low energy house. I commented that absolutely everything on it was built to perfection (such is the impression of Germany here in the UK) but he said that was the case 20 years ago but no longer, and a lot of stuff had to be re-made. Maybe there is a business model importing this stuff from Romania

Shoreham EGKA, United Kingdom
28 Posts
Sign in to add your message

Back to Top