LoW E glass explained

Two Minute Tips ... Low E Glass ... Technical Explanation

LOW E glass refers to the Low Emissivity Coatings that are placed on the surface of the glass when the glass is manufactured. There are two general categories of Low E glass, HARD COAT and SOFT COAT.

HARD COAT GLASS is made by applying the coatings when the glass itself is still in it’s liquid form. When the glass hardens, the coatings harden right into the surface. This method of producing Low E glass makes an extremely durable coating that can withstand handling during the manufacturing of the window. However, it does not produce the most efficient heat reflective surface.

SOFT COAT GLASS is made by applying the coatings after the glass is already cooled and hardened. The glass must be handled more carefully during the insulated glass manufacturing process, but once the insulated glass (IG) unit is sealed, the coated sides which face toward the interior of the two panes, are no longer vulnerable to damage. Soft Coated Low E glass can have an almost unbelievable ability to reflect the heat comes in contact with it.

Argon Gas is often used in the gap between the two panes of glass. The purpose of the ARGON is to inhibit convection currents inside the gap. Argon is a “NOBLE GAS” meaning the electrons in the glass do not move rapidly when exposed to infrared (heat) energy. This is helpful because if regular air is used in the space between the panes, the pane of glass facing the inside of your house will make the air inside the glass unit heat up and rise along the warm side of the glass. Then, as the air touches the exterior glass and gives up its heat to that pane of  glass, the air cools and sinks. This process continues very slowly all day and night, and it slowly transfers heat from the inside pane to the outside pane (in winter).

So the use of ARGON is one more way to save energy in your home. By the way,  ARGON is harmless to humans, it actually makes up about 1% of the air we breathe.  Some window manufacturers add KRYPTON to the airspace. It is twice as dense as ARGON, and is only useful if the airspace between the glass is very narrow. It also costs the manufacturer about 60 TIMES what argon costs, so it is used sparingly and is mainly used to “Enhance” the ARGON filled airspace.

See the short animation below to see how a convection current forms when regular air is used inside a piece of insulated glass. If ARGON is used in the gap between the panes, circulation will be almost nonexistant.