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My windows sweat in cold weather and it's chilly near them. In the summer, it's hot and my furniture fades. What is the best type of glass to get in replacement windows for year-round comfort? S. B.

Answer - There are several new types of super-efficient glass available to solve your problems. Some new low-emissivity (low-e) glass virtually eliminates wintertime sweating and cuts heat loss by 80 percent. The improved comfort is noticeable year-round.These windows block summer heat and more than 99 percent of the sun's fading rays. Much of the heat that comes through windows in the summer is reflected heat from patios, driveways and walkways. Low-e glass still allows the sun's direct short wavelength rays to pass through for winter solar heating.

The most recent residential glass innovation is switchable "privacy" glass. This efficient glass changes instantly from frosted to totally clear at the flip of a switch. This is ideal for bathrooms, bedrooms, etc.

A very thin liquid crystal film is laminated in the glass pane. When an electric current is applied to the film, it becomes clear. It uses a negligible amount of electricity, only one watt per sq. ft. One small electric controller can handle up to 100 sq. ft. of glass.

In the frosted privacy state, most visible light still gets through. This provides soft even lighting, yet blocks 60 percent of the fading rays. This can be combined with an additional low-e pane for super efficiency.

Filling the gap between sealed low-e panes with inert gas increases insulation value. Argon gas is most common. Krypton gas is more efficient.

These dense inert gases also block most outdoor noise transmission.

Krypton filled, triple pane glass with multiple low-e coatings (Super-R) is super efficient, up to R-8 insulation. Another efficient glass system (Insol-8) uses double pane glass with two clear low-e films stretched between them. This creates three krypton gas filled insulating gaps.

Not all low-e coatings are equally effective. Vacuum-deposited "soft coat"

(on inside sealed glass surfaces) has a lower emissivity than pyrolytic "hard coat". Hard coat is more durable and can be used for storm windows too.

Select windows with "warm edge" glass spacers. New spacer designs reduce heat loss and sweating around the window perimeter. Some use high strength very thin stainless steel instead of heavy gage aluminum to reduce heat loss. Others use a split spacer or molded-in thermal breaks.

Write for Utility Bills Update No. 739 listing 40 replacement window manufacturers, types of frames and glass each offers, and a glass selector chart showing R-values, summer shading coefficients and sweating resistance for new super efficient and switchable privacy types of glass. Please include $2.00 and a self-addressed envelope. Write to James Dulley, Deseret News, 6906 Royalgreen Dr., Cincinnati, OH 45244.

Question - I am considering installing an efficient tankless gas water heater in my utility room. I have been told to avoid using Teflon tape on the gas lines. Is it okay to use the tape or not? - T. T.

Answer - Tankless gas water heaters are a good choice. They are very efficient and provide a limitless supply of hot water. You should use the same gas piping procedures with a tankless water heater as with any water heater.

Tape is okay to use, but when you wrap the pipe threads, make sure that it covers only the threads, not the end of the pipe. Wrapping it sloppily can allow tape fragments to tear loose and get into the gas orifices.