USG Casting Fireplace Surrounds - Manual (Page 27)

In recent years, many fireplaces have been installed that are ventless, or are lacking a chimney or other means
of heat escape. These fireplaces only burn natural gas. Ventless fireplaces are manufactured to permit a blower to
be installed on top of the fireplace. This blower, which operates when the fireplace is on, blows heat from the fire
out into the room. Some people do not want the blower because they don’t want the heat, only the aesthetic effect
of the gas flame in the fireplace.
In terms of potential heat damage to fireplace ornamentation, a ventless fireplace with no blower represents
the greatest potential for damage because of the high temperature adjacent to the firebox. We do not recommend
that gypsum-based fireplace ornamentation be placed adjacent to a ventless fireplace without a blower. If the
fireplace is equipped with a blower, the temperature at the firebox is reduced and gypsum-based ornamentation
can be placed adjacent to it. All of this depends on the BTU rating of the firebox and exactly how close the surround
is to the firebox opening. High-BTU fireboxes with or without a blower, ventless or vented, could cause unwanted
heat-related effects to gypsum cement surrounds.
We recommend, when possible, that any fireplace surround made from gypsum cements be installed with
enough clearance from the firebox to prevent any heat-related damage. Again, we strongly urge you to learn about
specific fireboxes and inserts that will be associated with your products. Gaining thermal effect knowledge will allow
you to properly design surrounds for specific firebox BTU ranges and venting configurations.
Although rare, there are a few fireplaces where there are extensive bars and brackets around the fire box.
In use, these metal parts become very hot and over time will radiate heat onto surrounding surfaces. Radiant
energy can cause heat damage as well as thermal energy, but it is slower to occur. It can also be easily blocked so
that the energy is reflected away from areas that can be affected by heat.
27 Casting Fireplace Surrounds