What Type of Heat Transfer Does a Coating From a Window Reduce?

Hard Coat Low-e

• A hard coat low-e coating is applied at the factory to semi-molten glass as the window is being manufactured. Also known as a pyrolytic coating, it is typically applied in a gaseous state and actually becomes an integral part of the glass surface rather than a removable external film. A hard-coat low-e coating is transparent to light within the visible spectrum, but it reflects infrared light — otherwise known as heat — away from the glass. You may be able to detect a slightly hazy reflection when viewing hard-coated low-e glass under some types of lighting.

Soft Coat Low-E

• A soft coat low-e coating is factory applied to the glass in multiple layers in vacuum conditions. Also known as a sputter coating, it contains silver oxides and is usually a more expensive option. The soft-coated side of the glass faces inward to the window's gas filled interior cavity. Soft-coated low-e glass is more effective at blocking infrared light and is also more effective at blocking the ultraviolet rays that can fade colors indoors.

Blocking Solar Heat Gain Transference

• In the summer, a window manufactured with low-e glass will reduce the transfer of solar infrared heat to indoor rooms by 40 to 70 percent when compared with untreated glass. Windows that allow only a small amount of solar heat earn a low solar heat gain coefficiency (SHGC) rating. A multipane window's heat blocking performance will also be boosted by use of an argon gas layer to further resist heat transference. Homes in warm-weather climates should look for windows with a SHGC rating of 0.40 or less. In most cases, hard-coat low-e glass performs well in warm-weather locales.

Blocking Indoor Heat Loss

• During cold weather, a window with low-e glass can conserve indoor heating energy by preventing the glass from absorbing the heat and transferring it outdoors. This capacity is measured as a British thermal unit (BTU) factor, or U-factor for short. The lower the U-factor, the more effective these windows are at saving winter heating costs. Homeowners in regions with short summer seasons may also benefit from windows that have a higher SHGC because this would allow winter sunlight to help warm the home's interior. These windows would likely use soft-coat technology.

Select Windows Designed for Your Climate

• Window manufacturers can selectively engineer low-e coatings to optimize their infrared heat transference and heat transmission capacities. That's why window suppliers in four-season climates, for instance, offer products that differ from hot weather and cold weather regions. There is an ideal balance of U-factor and SHGC ratings for every variety of climate.