Low-E Windows: Green Tech That Can Start Fires

Low-emissivity (low-E) window glass is a green technology designed to improve building energy efficiency. It features a thin metallic coating that allows visible light to pass through while reflecting infrared heat. This reflection helps retain warmth inside during winter and deflects solar radiation in summer.

However, a potential side-effect arises when the glass is slightly bowed. In such cases, the curved surface can act like a magnifying glass. This phenomenon concentrates reflected heat onto a single point or along a line.

This focused heat has been known to cause damage, including scorching wooden decking, melting artificial turf, and harming plants. In more extreme situations, a series of fires were attributed to neighbors' newly installed low-E windows, prompting one homeowner to relocate a propane tank away from the focal point.

While architects are aware of and avoid curved reflecting glass in large structures to prevent "skyscraper death rays," the domestic version of this hazard may be less obvious. Any poorly manufactured low-E window carries the potential risk of igniting fires.