What is Low-E Glass?

To answer this, first let’s look at what low-E is.

Low-E is a very thin, almost invisible layer, applied to glass to increase its thermal efficiency.  Low-E stands for low emissivity. It is typically applied to glass in either one of two methods; pyrolytic or sputtered.  Pyrolytic low-E, also know as a hard coat, involves a process where tin oxide is baked onto the surface of the glass.  Forming a covalent bond with the glass, the resulting baked-on pyrolytic or hard coat low-E is extremely durable.  Alternatively, sputtered low-E makes use of silver oxide and is referred to as soft coat low-E.  Sputtered or soft coat low-E is applied in one, two, and three layers onto the surface of the glass.  Unlike pyrolytic low-E, sputtered low-E must be protected from humidity and contact.  Thus, sputtered (soft coat) low-E is applied to the interior surface of the glass that faces the sealed air space in a dual or triple glazed unit.

Now, those are all fancy, technical words, but what does that mean for you the homeowner?Low-E-window-diagram

Well for starters, it depends on where you live in the world and what your climate is like.  Depending on where you live, low-E is applied to different surfaces on an insulated unit; dual pane and/or triple pane glass.

Low-E is designed to deflect Ultra-Violet and infrared radiation.  In colder climates, the low-E is applied to the interior, inner-most surface to deflect heat back into the home, helping to reduce heating costs.  In warmer climates, low-E is applied to the interior, outer-most surface to deflect heat out of the home, reducing cooling costs.  The diagram to the right illustrates a dual-glazed insulated unit that is best designed for a warmer climate.  The low-E II denotes two coatings of low-E applied to the glass.

Choosing windows and doors that have low-E coating(s) on the glass can significantly reduce your energy costs each year.  A window or door’s energy efficiency is measured by its U-Value and SHGC ratings, which are directly effected by low-E.  When considering and comparing products that best meet your insulating needs, be sure to check these two ratings.




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  1. Low E Glass  April 29, 2014

    For hot climates, low-E coating should be applied to the outside pane of glass. If the windows are designed to provide heat energy in the winter and keep heat inside the house typical of cold climates, the Low-E coating will maximize benefit by being on the inside pane of glass.


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