Double Glazing – Air Gaps – What’s Best – Myth Vs Truth
Arm yourselves with the truth, give those sales guys a hard time!!!!
Over and over I hear that “the bigger, the better” makes the best air gap for energy efficiency, I hear this from customers who have visited suppliers who only have a 16mm gap (24mm glazing space), and a few suppliers who have argued this with me (briefly ) so I thought it may be useful to show the ASHRAE study which proves that 12mm is the optimum gap, not 16mm… (American Society of Heating Refrigeration and Air-Conditioning Engineers)
The graph below shows the “x” axis as the gap in inches (0.5 inches is 12.5mm) the vertical “y” axis shows the centre of glass U factor (or U value). The curves at the top of the graph refer to the outer pane and the lower curves refer to the inner pane.
You will notice that the curves for air/argon become elevated ABOVE 12mm, meaning that the U factor increases above 12mm. and the window becomes less energy efficient. Proving 12mm is the optimum gap for double glazing using Argon gas or air.
You can see that in all cases, at smaller gaps than optimum the U factor increases (gets worse) sharply.
Also as you can see, air gap (or Argon gap) is critical for energy efficiency and triple glazing has little value if the gaps are small (so double glazing with 12mm gaps is better than triple glazing with 6mm gaps).
Some local window manufacturers use gaps as low as 6mm in their double glazing as they have a very narrow glazing space, their windows being designed for single glazing – (check out the gaps you are being offered as air is free – today anyway ).
Remember 12mm = optimum and air is free, so when you buy double glazing you want a gap as close to 12mm as possible – you are already paying for the glass.
But remember WERS is your friend