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Understanding and Using Insulated Glass

Insulated or "double-pane" glass can be found in both residential and business construction. It is required by building codes in many areas as a mandatory energy conservation measure. And it really makes sense because single pane glass has virtually NO insulating value.

Storm windows can act in consort with your existing single pane windows to reduce heat loss. However, unless the storm windows are tightly closed they are ineffective as insulators. And, come on now... let's be honest... do you really close your storm windows every time you close your inside windows?

What is insulated glass?

Insulated glass consists of two panes of glass separated by a space. The perimeter of the glass is sealed, allowing no movement of outside air into the space. The space itself can be filled with dehydrated air, or with a special gas. The type of glass, the type of spacer, and the type of gas used in the space contribute to the overall insulating efficiency of the glass, and also the total cost. Graphic (left) courtesy BROSCO®

If you are purchasing a new home, doing a renovation, or just adding replacement windows, you want the best insulating glass you can afford. Review the window options with your builder, and have him place a dollar value on window upgrades. Only then can you be sure to get both quality and value in your windows.

What are the components of insulated glass, and how do they effect its efficiency?

Andersen® High-Performance™ or High-Performance Sun® solar control insulating glass

The effectiveness of insulating glass as an energy saver depends on the features incorporated into it. For example, above is a cross-section of a top-of-the-line Andersen® window. The features to be concerned with when purchasing insulating glass are the glass itself, the type of gas used in the air gap, the type of spacing material that holds the panes apart, and the material the window frame itself is made of.

The glass used in the manufacture of these windows may be coated or uncoated. Coated glass is typically called "Lo E", which means low emissivity. The coating is an extremely thin layer of metallic oxide that decreases the transmission of heat through the glass. Some of these coatings also decrease the passage of ultraviolet light (UV) into your home, which is notorious for causing fading in furniture and carpets.

The gas used in the space between the panes is dehydrated air in the least expensive panes, and argon and/or krypton gas in the highest quality panes. Argon and krypton gas have qualities that decrease the movement of heat through the space, giving improved efficiency. However, these gasses increase the manufacturing cost of the windows.

The third critical factor in the efficiency of insulating glass is the spacing material. Less efficient windows use aluminum as a spacing material... a poor choice since aluminum is a very heat-conductive material. Various companies have come up with better alternatives, such as stainless steel or composite metal/rubber combinations.

The final component actually has nothing to do with the glass at all. It is the material composing the window frame. Solid metal frames and tracks produce a net energy loss, since the metal pulls heat out of the house. This effectively negates much of the value of the insulated glass. Most newer windows are made either from wood, vinyl-clad wood, or metal with an insulating "break" between the inside and outside parts, resulting in less heat transfer to the outside.

When insulated glass gets broken, cloudy, or "fogs up" between the panes, what are the repair options?

Unfortunately, there is no do-it-yourself repair for clouded insulated glass. When the seal around the perimeter of the two panes fails (not IF, but WHEN, because they all fail eventually), moisture enters the gap and condenses on the inside of the glass, giving it a foggy appearance. This is irreversible. Often, the initial fogging is followed by mildew growth between the panes, making a bad situation worse!

You may be able to obtain an individual replacement glass panel, or have to purchase an entire replacement sash or door. A rule of thumb... metal windows and doors can usually be disassembled, wood sliding doors can normally be disassembled, but wood windows usually must be ordered as a complete sash.  You should contact a local representative of the manufacturer (home stores and lumberyards have relationships with many window/door manufacturers) to find out for sure.

If the window/door is a "stationary" unit, the un-installing becomes more tedious. Most have mechanical fasteners that keep the unit stationary, and they are often caulked also.  The large manufacturers, such as Pella and Andersen, offer help with the mechanics of uninstalling their products. They also have replacement glass available for all their windows... and you can order new panels without even disassembling the old ones for measurement.

"Mr. Cheap" brands may require some improvisation and trial-and-error to free them up. This is especially true if the moldings are painted, since all evidence of nail heads and order-of-assembly is lost beneath multiple layers of paint! Also, you may have to order custom-made glass to fit the "no-name" frames.

About ordering custom-sized insulated glass...

If you are unsure of your measuring skills, it may be wise to have the glazier make a house call and do the measuring for you. After all, you can still do part of the job, such as the initial disassembly of the window or door.

You can even take the glass panel or the entire door or window to the glazier! Then, after he gets the properly sized glass for you, finish the installation yourself.

Two final tips before you begin tearing the place apart...

  1. Don't begin disassembling the door until you have a definite source of supply for the glass and have talked to the glazier, window company or lumberyard. Though all brands do not proudly display their name on their products, there may be codes or other indications of the manufacturer's identity either on the glass, window frame, or even on the screens! Some customer-oriented suppliers are more than happy to visit your home and help you solve this dilemma!
  2. Depending on the door, you may not even have to disassemble it before ordering the new glass, especially if it is from a major manufacturer! They can use visible glass dimensions, for example, to pick the proper size replacement.

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