Important Things to Know About Buying Double Glazed UPVC Windows
High Performance Double Glazed UPVC Windows
The Importance of Double Glazed UPVC Windows Sealed Unit Air Gaps.
Without doubt, the glazing is one of the most important elements of any new or replacement window.
The introduction of the second pane of glass to create the modern double glazed window significantly reduced heat loss and also deadened the noise pollution from outside.
The insulation and noise reduction properties arise from the separation between the inner and outer panes of glass. Over the years, the gap between the inner and outer panes has been varied in order to make double glazing more efficient.
Why the size of the “air gap” in Double Glazed UPVC Windows Sealed Unit is important?
The air gap is the barrier between the outer and inner faces of the window, and is responsible for reducing heat transfer as much as possible.
If the gap is too small, then heat or cold could be radiated from one side to another. This effect lead to manufacturers increasing the size of the gap in the race to make the most efficient double glazing.
However, there is a problem that develops if the gap is too wide, as the air in the gap can begin to circulate.
Circulating air within the gap (cold air moving downward from 1 side, warm air moving upward from the other) will ruin the insulation.
Currently the size of the gap ranges from 6mm to 20mm.
What is the best option?
Sealed units for UPVC windows, as mentioned above, can come in thicknesses of 6mm to 20mm. Each pane of glass is usually 4mm thick, so that makes the overall thickness range from 14mm to 28mm.
The performance gain from single glazing to 6mm double glazing is significant. The performance gain from 6mm to 12mm / 14mm is also good, 14mm to 20mm not so great an increase.
The gain in performance is not linear – meaning that doubling the size of the gap does not double the insulation.
The industry mostly agrees that 14mm to 16mm is perfectly adequate for the majority of circumstances.
The 28mm double glazed window is currently marketed as the best option around. That is a combination of a 20mm air gap plus the glazing (2x4mm).
Important things to know about buying double glazed UPVC windows
There is typically a higher price for 28mm units, which may or may not be justified by the increased savings on your energy bills. More importantly, however, is the quality of the product.
A lot is made in the industry about using gas filled sealed units. The most common gas used is Argon. Argon is thicker than air, preventing circulation and boosting insulation properties for both heat & sound.
If the window is of low quality, all the Argon gas could have leaked out within 2 or 3 years. A high performance UPVC window can reduce that loss to around 1% per year.
As a general guide, Argon filled units are better than non-Argon filled units, but you should not be talked into paying a silly amount extra for this feature.
It bears repeating that the industry itself mostly agrees that 14mm to 16mm (22mm to 24mm overall) is perfectly adequate for the majority of circumstances.
You are likely to “get what you paid for”
The fitting of your new or replacement UPVC windows is going to be important also. If the windows are poorly fitted, then all the above gains will be lost.
It makes sense to get at least 4 or 5 written quotations from different installers. You should also take references from previous customers to get a better “feel” for the installer in question.
Cheap is not always “cheerful” and it can make sense to decide based on the best value for money for your circumstances rather than choosing based just on the headline price.