The Lowdown On Low-E Glass

If you’re like most homeowners, you want as much control over your internal/external temperatures as possible, not only for your family’s comfort but also for the sake of your utility budget. It’s one thing simply to stuff a bunch of insulation inside solid walls, but what the heck are you supposed to do about your windows? Glass is a great material for transferring heat and cold from one side to another – which is exactly what you don’t want. Well, here at Zen Windows Austin we have a couple of different strategies for dealing with that issue. We can set you up with double-pane, argon-insulated windows, or we can install windows containing low-E glass.

Low-E GlassLow-E glass is fascinating stuff, but how it’s made and how it works requires some explanation – starting with the name. “Low-E” is short for “low emissivity“, and emissivity is the amount of radiant thermal energy (a.k.a. heat) a substance allows to pass through it. Think of reflectivity as its opposite. The more reflective a surface is, the less emissivity it has and vice versa. Normal, non-tinted glass has an extraordinarily high emissivity rating of 0.91. Shiny metals such as aluminum and silver, however, have emissivity levels at or below 0.02.

Can you see where this is going? Low-E glass has been coated with a transparent, unbelievably thin layer of silver or tin oxide particles. This layer acts just like the shiny surfaces of a Thermos bottle. It reflects heat radiating outward back inward, preserving the interior warmth of your home on cold days. It also reflects incoming radiant energy to bounce that heat away instead of allowing it to get in, keeping your home cooler on those hot Austin days.

There are two different methods for making low-E glass, and which type of glass you choose will have some influence on the results you get. Passive low-E glass is produced through a pyrolytic process in which a tin oxide coating is fused onto large sheets of manufactured glass before the glass has been cooled and cut into specific sizes. MSVD low-E glass is made by a different process known as magnetron sputtering vacuum deposition. A silver-based layer is added to the already-cut glass and then sealed inside another layer of lamination. The low-E layer or layers can be added to face one direction or both directions, providing one-way or two-way effects.

What’s the bottom-line difference between passive versus MSVD glass in terms of temperature control? Passive low-E glass will have a higher U value than MSVD low-E glass, meaning that it does a better job of keeping warmth in than keeping it out. (This makes it great for cold climates.) MSVD glass is also called “solar control” glass because its strength lies in the opposite direction; it has a higher solar heat gain coefficient, which makes it more effective in blocking incoming heat from the sun’s rays than passive low-E glass. Zen Windows Austin can help you choose the right low-E glass for your Austin window replacements – just ask!