Glass blocks can be as energy efficient as windows

Posted12/1/2013 12:32 AM

Q. My house needs more efficient windows. I live alone, so I am considering some glass block windows for security. Are they very efficient and how can I have some summertime ventilation with them?

A. Glass block windows are definitely more secure than standard double-pane glass windows for several reasons. Although it is possible to hammer one's way through a glass block window, it is certainly is much more difficult and noisy than breaking through standard pane glass windows.


If the individual blocks are mounted with concrete between them, this makes it even more difficult to get through. For the greatest security, completely solid glass blocks are available. These are less energy efficient than standard hollow glass blocks and are very heavy to install. These are more often used in high-security commercial applications.

Although most people think glass blocks are solid, most residential blocks are actually hollow. Two hollow halves are fused together under high heat. Once they are sealed and cool down, the air inside them contracts. This creates a partial vacuum which increases their insulation and efficiency.

Another efficient option is plastic blocks which look identical to glass blocks. They are often molded from acrylic plastic and are also hollow for efficiency and lighter weight. Acrylic plastic does not yellow over time and its natural properties block nearly all the sun's UV (ultraviolet) fading rays.

Both glass and plastic blocks now have high-efficiency features of regular windows. For example, low-emissivity coatings are deposited on the inside surface of the block before it is fused together. This helps to keep heat indoors during winter and the sun's heat out during summer.

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The most efficient plastic block windows have a film stretched in between the two halves. This creates two dead air spaces inside the block. A low-emissivity coating is deposited on this film to produce R-3 insulation.

During summer, block windows act like mini-louvers to reduce the sun's heat. The concrete, or other opaque material, in between the blocks creates shade, particularly on south-facing windows when the sun is high in the sky. During winter, the rays from the lower sun shine through for solar heating.

There are several options for ventilation through a block window. One is to replace several of the blocks with a narrow horizontal awning window which can be opened. The small opening is too small for someone to crawl through.

Another ventilation option is to install a casement window made entirely of plastic blocks. This swings open similar to a standard casement window and has multiple latches for security. This type of block window is installed just like a standard replacement window in the existing wall opening.


The following companies offer glass and plastic block windows: Builders Accessories, (888) 921-7086,; Circle Redmont, (800) 358-3888,; Glashaus, (800) 345-7381,; Hy-Lite Products, (888) 256-2599,; Pacific Accent, (888) 522-4527,; and Pittsburgh Corning, (800) 624-2120,

Q. We are remodeling our kitchen and getting all new appliances. We want to be as efficient as possible. Does it make much difference where we locate the various appliances in the kitchen?

A. The location does have an impact on the cost to operate kitchen appliances. The most important factor though is still the efficiency of the appliance itself. Select ones which are Energy Star qualified.

Locate the refrigerator in the coolest location. This means not in the direct sun from a window or next to the range or oven. Locate the range or oven away from drafts (window or door) which might carry away heat. Locate countertop areas near natural light sources.

• Write to James Dulley at 6906 Royalgreen Drive, Cincinnati, OH 45244 or visit

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