Locally, as in much of the Northern hemisphere, most new windows on buildings are constructed of two sheets of glass, with an air (argon) gap between them.

In addition, the middle side (against the argon gas) of the pane closest to the interior of the building, typically has a low emissivity coating ("Low-E") to reflect heat back into the building.

Our new home ("The Pumpkin") has such windows. Whilst playing with a thermal imaging camera the other night, we noticed a peculiarity on one side of a matched pair of windows: the left side pane had condensation on the inside of the home, and was reflecting more heat inward than the right side pane.

So something strange was happening there.

A bit of googling revealed a simple trick to check whether/where a window has a Low-E coating: hold a butane lighter (lit) up close to the glass, and observe the reflections of the flame. There will be two primary reflections (inner, outer) from each of the two sheets of glass, or four (primary) reflections in total.

The side of the sheet of glass which has the Low-E coating will reflect a more greenish blue version of the flame than the others.

Sure enough, this works. We examined the two windows, and determined that the left side of the pair had the Low-E coating on the inside (the home) surface, rather than on the argon side. So somebody at the factory must have lost track and assembled the two sheets incorrectly.

So we then decided to check the rest of the house, and discovered one other window with an anomaly: the largest pane on the lower level of the home has no Low-E coating at all!

We'll get the glass from both affected windows replaced under warranty, so no problem there. But the trick with the lighter seemed nifty enough to warrant a posting here too!

This method also works with a Cree flashlight, but the colours are not as obvious as with the soft butane flame.

Cheers
Mark


Attachments
flames.jpg

Description: Butane flame reflections. Can you tell which one, counting from the left, indicates a Low-E coating?