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6 Feb 2007

When Double Glazing Goes Horribly Wrong…

tw1Double glazed windows work because they had a vacuum between the two panes of glass (or three if you are fortunate enough to have triple glazed windows) which stops the heat passing between the two. Energy advice books will often tell you to keep an eye on your double glazed units, if condensation starts to appear between the panes, it is an indicator that the vacuum has gone, that the window is doing very little in terms of energy efficiency, and it needs to be replaced (seeing dead flies or childrens’ toys in there indicates the same…). As I returned on the train the other day from doing a talk in Penzance (for Transition Penwith, a very vibrant bunch…), I noticed that the window next to me was the next step on, a great example of how to tell when you should have replaced your double glazed unit about 4 years ago.

tw2It was very impressive. The space between the two panes of glass contained about 4 inches of water. Each time the train started to go up a hill the water would slosh down to one end, sloshing back again when the train went downhill again (see right). It was very diverting, although strictly speaking not best practice from an energy efficiency point of view. Of course it may have been deliberate. First Great Western Trains may be planning to keep small fish in the gap, in order to give people something entertaining and relaxing to look at while their train is broken down in a siding outside Reading for 4 hours. A bit like painting psychiatric hospitals pastel pink to calm everybody down a bit, perhaps fish tank windows are the new policy for preventing ‘rail rage’.

Anyway, the point of this somewhat pointless post is that if you have double glazing, and the space between you glass contains 4 inches of water, you should really think about having them replaced. Or make a statement of it and get some fish in there. Or tiny remote controlled submarines (I’m sure you’d find some on Ebay), which could keep you amused for hours. Or perhaps some kind of worm bin type thing like we made in school as children where you can watch the worms burrowing through the organic matter (although this might make your room a bit dark). It is also clear that if you have such windows you are probably the kind of person who leaves things until the last minute, never a very good trait, especially as that appears to be humanity’s collective response to climate change. The advice for someone with misted up double glazing units is the same for a species living on a planet experiencing the warmest year on record and with melting icecaps, time to get it sorted out…

Categories: Climate Change, General

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Mark Forskitt
6 Feb 8:55am

There is another very good reason for getting your double glazing sorted out sooner rather than later. The embedded energy in glass is very high. Put another way – as oil and energy prices increase, the more the cost of double glazing increases.
Make sure you put the old glas to good use – home made solar collectors, or cut down to make cloche are both good, much beeter thatn using a load more energy recycling it into mroe glass.

8 Feb 2:42am

Most double glazed windows are filled with air or Argon. Evacuated units are relatively rare. For one thing the typical eighth inch glass panes would break from atmospheric pressure pushing on the outside.

Robert Lauder
8 Feb 12:44pm

You can’t find buildings with panes of glass 1m diagonal built before the 1940s.

I can envisage a farm field full of the things for use as single sheets when the machinery to make large panes of glass can’t run. Breaking a large flat, clear pane will be seen as yet another really dumb thing we did back when…

I think storing them (under a walnut tree obviously), would be a shrewd long term investment.

21 Feb 10:22pm

No vacuum in regular double or triple glazing but university of ulster have invented a real evacuated pane with thousands of little needles holding the glass apart. Very, very good insulation and they use less resources to make. Noones making them commercially yet.

23 May 9:19pm

I worked for British Rail Derby works in the sixties
and this problem was common in the DG units,I think the max amount of water I noticed in one window was about three quarters way up it.
I remember they had a air pump to pump dry air through the unit to dry it out without taking the window out.

Guy Mercer
12 Feb 11:47am

Water accumulates from condensation as air is pumped in & out through a small leak above the bottom due to temperature changes.
The insulation is from “still air” between the glass, hence 20mm (3/4 inch) gaps are the best. Any wider and circulation currents reduce the insulation value.
To Get rid of the water drill a small hole (3mm 1/8 ins )in the bottom of the unit that drains to the outside of the window. It will not reduce the insulation properties and air sucked in ( when the unit cools) will be from outside which will be drier than the air in the unit.
You may get internal condensation ( which can freeze on the outer pane) when the temperature outside cools rapidly, but it will always dry out.