Heat-Resistant Tempered Glass

This glass is standard in all the millions of fireplace doors made during the past 50 years. The glass can withstand constant temperatures of 470°Fahrenheit. When it is more than six inches from the flames of a wood fire, it stays below this temperature, and therefore has an extremely long lifetime (over 80 years).

If tempered glass is exposed to higher temperatures, it AGES more quickly, which means that it loses its TEMPER. No, it doesn't get angry. It just loses some of the special characteristics built into it by the glass manufacturer, (mostly by the way they cooled the glass down when it was made). If a piece of tempered glass is exposed to temperatures of about 800°F, the 80 year lifetime shortens to about 15 seconds!!

Nearly all JUCA models have large enough fireboxes that the flames are more than six inches from the glass, so Tempered Glass is the appropriate material. That's why we can use tempered glass as standard in our B-3B, B-3C, B-3D, F-9A, F-9AX, L-8 and L-10 Models. Only in the very smallest-firebox JUCAs (K-3, B-3JN, B-3N), is the normally optional Pyroceram material (below) used. If you've been paying attention, you have noticed that there is one JUCA model that we have not mentioned, the B-3J. This unit is near the borderline. If people expect to use it hard, we recomment the Pyroceram. If it will be used only occasionally, the standard tempered glass should be fine.

Only if a large-firebox JUCA is regularly abused, should it be necessary to consider the optional Pyroceram in those units.

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Super Heat-Resistant Pyroceram

Technically, this is not actually a glass, although it certainly seems like it. It is actually a transparent ceramic material. The advantage of this is that it has an extremely low thermal coefficient of expansion, which is a high-class way of saying that it doesn't try to change size very much when heated or cooled.

The advantage of this is when the material is suddenly heated or cooled by a lot, no substantial internal stresses develop (as in tempered glass), where part of the panel is trying to get larger while other parts stay the same dimensions, which is the main cause of breakage in tempered glass.

This material can continuously tolerate temperatures of 1200 degrees Fahrenheit, and never ages as a result. Some suppliers of ours even guarantee that it will NEVER break due to a wood fire! The only down-sides of this material, when compared to tempered glass is that it is not as Impact-resistant, and it costs about three times as much!

The design of most JUCA units includes a huge firebox, where the glass panels are at least 6" away from the flames, and so the design temperature of the glass in those units is about 350°Fahrenheit. That being the case, the less expensive Tempered Glass (which can easily handle 470°F) is appropriate, and has a design lifetime of over 80 years.

Some smaller firebox JUCAs (the K-3 and the B-3JN, for example), DO have Pyroceram as standard. Nearly all owners of the bigger firebox JUCAs have their Tempered glass last many years. A small number may experience shorter lifetimes for the standard Tempered Glass, and so these individuals should consider this optional Pyroceram material as a replacement.

In the spirit of completeness, there are a couple other products that are considered for glass panels on fireplaces and woodstoves. Vycor actually existed before Pyroceram and was developed for the windows of our early spacecraft. It has great heat resistance (1800°F), limited impact resistance, is generally very thin, and is extremely high priced. Before Pyroceram, we used to use Vycor as the optional glass. Pyroceram (1300F°) still has way more heat resistance than needed in our products, and it is physically less fragile.

Pyrex and Tempered Pyrex. Coffeepots and all kinds of other glass things for the kitchen stove are made of this stuff. It sounds promising! It's not! Many years ago, we bought a whole bunch of it. It's lifetime in woodstoves seemed to be about one day! Avoid it!

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