Consumer Tips

Thermal Windows, Restoration/De-Fogging

Windows and doors are typically responsible for about 40 per cent of your home's heating bill. Thermal windows are typically two to four times more efficient than older single pane windows. That means you can expect your winter heating bills to drop on average about 20 percent to 30 percent.

Thermal glass is comprised of two panes of thick glass separated by an insulating spacer. The cavity created by the spacer frame provides an "air chamber" between the two panes of glass, which improves the insulating properties of the window. The two panes of glass and the insulating frame form a hermetically sealed unit that prevents the passage of air and humidity.

Argon is one of the most popular gasses used to fill the space between the two (or three) panes of glass in a thermal window. Argon is considered a good insulator.

Warranties are generally 10 years or greater.

If you notice any condensation inside a thermal window, then humidity is finding its way into the space between the two sealed panes of glass.

In most cases, this means that the seal has been damaged and the window must be replaced. In addition to the risk of the glass actually breaking, a thermal window with a damaged seal can, according to some estimates, lose up to 50 per cent of its thermal efficiency.

Explaining Condensation

There are some people who believe that foggy windows may be caused not only by seal failure or but by something referred to as "solar pumping".

Solar pumping is described as naturally occurring during the change from day to night, where sunlight heats the inner airspace of the thermal window cavity during the day and causes the window to pressurize, which forces out small amounts of air within the window cavity through the semi-permeable seal. In the evening, as the temperature drops, the window cools and creates a low pressure area causing small amounts of air to be drawn back into the inner window cavity. The air being drawn back into the window naturally holds moisture and this moisture is absorbed by the window's desiccant material.

In this scenario, the thermal pane window will eventually lose the ability to absorb condensation and fog up.

The Process

Many industry experts view the appearance of condensation as indication of seal failure and, therefore, a signal that it is time to have the window replaced.

However, there are companies that offer a service called window restoration or "de-fogging". The process is marketed as an affordable solution to replacing foggy thermal windows.

Here's how the process often works:

Holes are drilled at top and bottom of the window (glass portion). A solution is often used to clean the glass and remove any stains. The moisture is removed using a one-way valve, then the holes are re-filled. During this process, the argon gas inside the windows, which provides the insulation, is removed.

While this process may restore the aesthetic value of the thermal window, claims that is also restores the R-value--which is a measure of thermal resistance used in the building and construction industry--should be substantiated.

Many industry experts have advised BBB that this process may not deal directly with the cause of the condensation (either a broken seal, improper installation, or a manufacturing defect) and be only a short-term solution. The process may also reduce the effectiveness of the window in terms of its energy efficiency.