I want to install some new windows, but I want them to provide security against break-ins and be energy-efficient. Are glass block windows very efficient and can I install them myself to lower the cost? R.M.

A - If you are concerned about security, privacy and efficiency, glass block windows can be an excellent choice for your house. You have many options as to the patterns from totally clear for a view to more privacy still with outdoor light transmission. There are several new do-it-yourself application kits available.Each individual glass block is not a solid block of glass. It is two hollow halves fused together under high temperature. As they cool, a partial vacuum is formed inside them. This vacuum helps to improve the insulation value of the glass block and reduce heat loss and heat gain. Some blocks are made to go around corners or have curved contours.

Since they are set in mortar, glass block windows are extremely airtight. This not only reduces drafts and saves energy, but it minimizes dust and dirt and outdoor noise. They are basically maintenance-free. With the pattern on the inside surface of the glass block, the smooth outside surfaces are easily cleaned.

For south-facing windows, the glass blocks provide natural solar control.In the winter, with the sun lower in the sky, it will easily shine in the glass block windows. However, in the summer with the higher sun position, the mortar joints block the sun and effectively become automatic louvers.

There are several do-it-yourself options available for glass block windows. One type is a pre-made glass block unit that can include operational ventilation louvers. You simply buy the custom-sized unit complete and install it in your window opening.

Another system uses a clear plastic spacer strip to position the glass blocks. When the glass block window is completed, it has a complete-glass look and allows more light transmission.

You simply cut the plastic strips to the proper lengths (both vertical and horizontal joints) and stack up the glass blocks in the window opening. Once they are in place, you fill the joints with standard clear silicone caulk to seal and secure the glass blocks in place.

If you want the standard mortar joints, you can use special plastic corner spacers to accurately position the glass blocks in the mortar. After the mortar is set, you twist off the exposed spacer ends and repoint those spots. The spacers are totally hidden inside the mortar.

You can write to me for UTILITY BILLS UPDATE No. 103 showing the various sizes and efficiency specifications of glass block windows. Write to James Dulley, The Deseret News, 6906 Royal Green Drive, Cincinnati, OH 45244. Please include $1 and a self-addressed STAMPED BUSINESS-SIZE envelope.

Q - I have often heard the term "quads" when referring to energy usage of the United States. What is a "quad" of energy and how can I relate that to how much energy I use in my home? M.V.

A - A "quad" is one quadrillion Btu of energy or heat. One quadrillion Btu is 1,000,000,000,000,000 Btu. In 1985, the total amount of energy used by the entire world was 225 quads. In order to relate this to your home, 100 hours of color TV uses 28,000 Btu. Making a cup of tea uses about 500 Btu and a pound of firewood contains about 6,000 Btu of heat content.