Double glazed windows are made out of two separate panes of glass, separated by a 1/2″ to 3/4″ of argon gas. These panes are permanently sealed in place in an airtight frame.
Why they are important
Glass is effective at conducting heat. You only need to put hot coffee in a water glass to know just how fast heat transfer can happen.
Double-glazed windows, instead of relying on glass for insulation, instead relies on argon gas.
Conduction versus Convection
Argon gas molecules, individually, are an excellent insulating material. It takes a lot of energy to heat up and cool down air. Air is called conduction-resistant.
The reason this might be surprising is that air in our atmosphere seems to change temperature rapidly. However, this only happens because of convection, or the mixing of air of different temperatures by air currents. Convection causes rooms of air to heat up quickly, even though each individual molecule is resistant to changing temperature.
The great thing about double glazed windows is that the argongas between the panes is too narrow for effective convection. Air currents don’t develop, and the air doesn’t mix. Even better, the airtight seal on a double glazed window prevents any indoors or outdoors air currents from causing the argon gas inside the pane to move or mix.
Instead, the argon gas becomes a still blanket that insulates the window against conduction. Engineers call this a dead air space.Dead air space is very insulating, and is actually the main method used in thermoses and travel mugs to keep drinks warm.
The installation options of double glazed windows are also much better than traditional windows.
Traditional windows typically are made up of sliding panes of glass along rubber or plastic tracks in the window frame. These are never fully airtight. Air currents from both inside and outside the house can seep into the space between the panes, compromising the dead air space. Even worse, air from outside can actually get inside by seeping through the seals on both panes of glass.
By contrast, double glazed windows typically open via a crank mechanism, instead of a sliding mechanism. When closed, they can be locked with a lever to create a perfect seal.
Condensation occurs on the inside of windows when the air outside is cold, and on the outside with the air outside is hot and humid. Both scenarios are bad, as condensation can damage your paint and drywall. However, both situations can be avoided by using double glazed windows. The argon gas sealed inside double glazed windows is de-humidified, so no condensation occurs inside the window itself. The extra insulation greatly slows the temperature changes, so neither pane of glass even has a radically different temperature from the air it is exposed to. This prevents condensation from developing either inside or outside your home.
Double glazed windows are the wave of the future. They only cost slightly more than traditional windows, but will save you literally thousands of dollars in energy savings and renovations.