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Architectural Glass – Low E-Coatings

Alpen Windows’ unique super-insulating glass system uses an advanced combination of low-e coated glass, Heat Mirror suspended coated film, insulating gas fill and warm-edge spacer to deliver high performance in architectural glass and our fiberglass window products. Of all of these materials, low-e coatings are one of the key drivers of performance and ability to customize performance for climate, orientation, direction and occupant needs.

What are Low-E Coatings?

Glass is naturally considered to have a high-emissivity characteristic. To better understand this, think of your morning coffee cup, when you pour hot coffee into a glass cup you can easily feel the heat transfer from the coffee to the coffee mug. This example applies to the glazing in your home’s windows as well: if you have clear glass panes in your windows, in the winter heat from inside your home has a low path of resistance to conduct from inside your home to outside. A similar effect happens in the summer but in reverse, outdoor heat conducts through the high-emissivity glass (low resistance to heat transfer) from outside into the home you are trying to keep cool.

Low-emissivity (low-E) coatings are a way to raise the resistance to heat transfer, or lower the emissivity, of glass in window products. In essence, low-e coatings act as a thermos would for your coffee cup; it helps control where to keep the heat, either indoors in the winter or outdoors in the summer.

Alpen Heat Mirror SkylightLow-E began to be used widely in the window industry starting in the 1970s with the first pyrolitic- or Hard Coat- low-e coatings.  Since then, a wide variety of coatings have been developed and adopted to perform multiple functions from thermal performance enhancements to glare reduction to solar heat gain control as well as add many aesthetic characteristics.

Low E is comprised mostly of silver, titanium and iron-oxide molecules that are “sputtered” (think spitting or spraying an invisible mist of metal) onto a sheet of glass.  You can actually sputter-coat glass with any kind of metal – even gold!

How Does Alpen Use Low-E?

Alpen uses unique combinations of low-e applied to glass panes and our Heat Mirror suspended coated film to build an energy efficient, high performance glazing unit. The coating works by reflecting back heat to its source; in the winter the heat is reflected back into the house and in the summer the sun’s excess heat is reflected back outside. And, because Low-E coatings are Spectrally Selective, different coatings allow varying amounts of long-wave infrared heat to pass through the glass, while still blocking 99.9% of the damaging UV rays.

Low E Solar Control

Alpen Windows low-E coatings reflect excess solar heat back outside in the summer and block harmful UV rays


Winter Passive Gain

Alpen Windows low-E coatings allow passive solar heat into your home in the winter while blocking harmful UV rays

There are several types of low-E coatings available on both glass and Heat Mirror suspended coated film that can be combined to benefit benefit each climate differently. In cold climates like Boston, a home can save more energy if it uses super-insulating windows that maximize solar heat gain in the day and minimize heat loss at night. In hot climates, like Phoenix, the reverse would be true.

Alpen HPP understands that one of the best ways to save energy in your home is by utilizing the appropriate low-E coating and thermal performance for your individual climate and your home’s unique orientation towards the sun. Our super-insulating glass packages are carefully engineered to provide optimal performance for a variety of climate zones, so that both energy savings and comfort can be achieved.