Living in sunny southern California, many people choose to tint their home windows as a way to save on utility bills and to keep the sun’s hot rays to a minimum. However, something may be happening that can be far more costly to repair than what is being saved on elevated utility bills.
Thermal Window Anatomy
A thermal window has dual or even triple panes of glass that are separated with spacers, leaving open air spaces between the panes. In the window industry, this assembly is known as an IGU, insulated glazing unit or glass unit. You will also hear these windows referred to as thermopane, insulated, dual or multi pane windows. On my home inspections, I usually hear others refer to this type of window as dual pane. The air space between the panes of glass is removed under negative pressure (vacuumed) and replaced with inert gas, like krypton or argon, which slows the transfer of heat through the window because gas is less heat conductive.
Now, let’s talk about failed thermoseals in dual/multi pane windows. A failed thermoseal occurs when a multi pane glass, for instance a home window or slider, develops condensation or fogginess that can’t be wiped off from either side of the window. The cause is a failure in the edge seal that secures the individual panes of glass. If the fogginess is severe enough, the window will more than likely have to be replaced.
When applying window film to dual pane windows, the film is placed on the interior side of the window. As the weather warms up, the film may reflect heat back through the panes. The interior gasses trapped in the panes can expand and contract as the temperature rises and falls, causing the unit to swell and constrict, which may cause breaking of the seals to fail, and the inert gas to escape, and in some cases the glass may even shatter. Another factor here is heat absorption. As a general rule, any film that has a solar heat absorption rate of 50% or greater is not safe on dual pane glass.
Here are the most common tints that are not safe to use:
Natural 20% VLT
Broze 20% VLT
Blackout film and automotive film
Luckily, today’s many window tints are generally safe to use, and as an added reassurance, hire a professional installer. Last note, keep in mind that tinting can also void the window’s manufacturer warranty, so be sure to check with your window manufacturer first.