11/01/2012 - Is triple glazing worth it?

It seems that what ever you read in our industry press, the new must have is triple glazing.

Obviously the glass industry is on board as each unit has an extra 50% of glass in it.

But is it green or even sustainable?

Before we look at the potential savings lets look at the costs: The unit will cost more because it has more glass content & takes longer to manufacture. It weighs 50% more so therefore costs more to transport in fuel.

One would imagine that you would need a fantastic saving to make the above work for you.

Lets see:

28mm warm edge, argon, softcoat has a centre pain U value of 1.1

The same unit with a center pane of softcoat would be 1.

In Liniar we can do 36mm sealed units so how about a 36mm triple glazed unit with warm edge, argon & the two softcoat panes.

This is a U value of .9

Just as an aside if the center softcoat is swapped for clear it is the same U value.

So there we have it a 28mm triple glazed unit over a 28mm double glazed unit makes a U value difference of 0.1.

A 36mm triple glazed unit over a 28mm triple glazed unit makes a U value difference of 0.2.

It seems to me that it would take quite along time to offset just the increased costs of manufacture & transport never mind the question of sustainability.

But lets have a go at calculating the saving that a difference of U value of 0.1 makes.

Assume 20m2 of window (180m2 house).
Average annual temp is ~9 degrees for the UK. Internal temp maintained at 20 degrees.

Heat loss due to 0.1 w/mK = 0.1 x 20 x (20-9) = 22W

Heat loss per year = 22 x 24 x 365 = ~192 kWh

CO2 emissions (assuming gas heating at 0.194Kg/kWh.) = 37 kg
Assuming average household emits 9 tonnes CO2 a year, this is equivalent to 0.4% of household emissions

Cost saving (assuming gas at 4.2p per kWh) = 192 x 0.042 = £8.09

So, going to windows with an 'improved' U value of 0.1 saves 37 kilos of CO2 a year, or about eight quid. Which could pay for the extra cost of the sealed unit in about 50 years or so.

I will leave you to make your own minds up.