Where should Low-E Coating be installed?

  • 0

Where should Low-E Coating be installed?

Category : Replacement Windows

How does Low E work?

Where should the low-e coating be installed?

To be most effective in climates where you want to block heat loss but allow beneficial solar gain to enter, the low-e coating should be located on the outer surface of the inner pane of glass–in the window industry, this is known as the #3 surface (in denoting surfaces, you always start with the outermost surface). In warmer climates where you’re more concerned with keeping unwanted heat out, the preferred location for the low-e coating is the #2 surface (the inner face of the outer pane of glass). I remember seeing a German window one time with a sash designed to be flipped seasonally to optimize the low-e coating location (those Germans!), illustrating that point.

While those low-e placements (#2 or #3 surface) are preferred, having the coating on the other surface isn’t the end of the world. The difference between the overall energy performance of the window with the #2 vs. #3 surface in any climate is far less significant than the the difference between having a low-e coating and not having one. Some manufacturers only put the low-e on the #2 surface, citing concern about seal failure when the coating is on the #3 surface. That’s not a huge problem even in a cold climate.

With low-e coatings directly deposited onto the glass there are two broad categories: soft-coat and hard-coat. With soft-coat low-e, a thin layer of silver is deposited onto the glass through a sputtering process after the glass has been manufactured. While the earliest soft-coat low-e had a single layer of silver, coatings with two layers (low-e squared) and three layers (low-e cubed) came along since that have even lower emissivity and lower heat loss. These sputtered coatings have been referred to as “soft-coat” because the coatings remain fairly delicate and have to be protected within the insulated glass unit (facing the air space)–though that might be changing, as described below.

With traditional hard-coat low-e, a low-emissivity layer of indium tin oxide is applied when the glass is still molten and just beginning to harden in the float-glass “lehr” where it is produced (see last week’s blog for a description of float-glass manufacturing). Denoting the high-temperature production, these coatings are also referred to as “pyrolytic” low-e. The indium tin oxide becomes part of the glass and, as a result, the low-e coatings becomes more durable. That’s why hard-coat low-e is the type of low-e preferred for storm windows where the coating has to withstand washing and other abrasive actions.

While hard-coat low-e is more durable than soft-coat, the emissivity isn’t as low, so these glazings don’t achieve as low a U-factor. On the other hand, they allow more sunlight to pass through, so they are usually better for houses that are relying on passive solar heating.

What’s new with low-e?

The distinction between soft-coat and hard-coat low-e is getting muddier. Cardinal Glass recently introduced an ultra-clear sputtered coating for glass (LoE-i89) that can be installed on the #4 surface of an insulated glass unit–the surface of the glass facing the room. According to Jim Larsen of Cardinal, this glass provides a remarkably high visible transmittance of 89%–significantly higher than standard pyrolytic hard-coat low-e glass. He described this to me as a “sputtered hard-coat,” with the “i” standing for indium. The coating is durable and it doesn’t have the bluish tint that some people object to with pyrolytic hard-coat low-e.

Glass with this coating can be combined with a low-e-squared or low-e-cubed glass to achieve a center-of-glass U-factor as low as 0.20 (R-5) with a double-glazed window. Previously, we needed triple glazing to reach this level of energy performance.

Cardinal also recently introduced a new high-solar-transmission soft-coat LoE-180 (80% visible light transmission), which is a single-layer soft-coat low-e. This provides significantly greater solar gain than the original single-layer soft-coat low-e glazings.

Leave a Reply

Read more about Energy Star

Energy Star partner, denver replacement windows

Questions or comments?


* indicates required field
Denver Installation masters, denver window replacement, window replacement denver

Looking for an Andersen Service Provider?

denver replacement windows colorado, doors, trwindowservices, denver

Click here for the nearest Andersen Service Center