USG Casting Fireplace Surrounds - Manual (Page 5)

Due to the wide variety of fireplace inserts that are replacing traditional
masonry fireplaces, it is important to understand how the inserts’
temperature profiles can affect cast fireplace surrounds. There is
no comprehensive public source for technical information (mainly
thermal mapping and the impact on surrounding areas) that is so
crucial to the design, style, and formulation of fireplace surrounds,
and yet ignorance of these issues can be life-threatening. Fireplace
inserts should be UL-rated since there is a life-safety issue. Since
it is impossible to know the heat-related effects for all potential
combinations of surrounds, fireboxes, and inserts, we strongly
recommend that you contact insert manufacturers for thermal profile
information for their products.
Fireplace Circulating Firebox A fireplace with multiple-wall construction around the fire chamber that permits air to circulate between the walls,
Insert Types become heated, and enter the house directly or via short ducts. This firebox typically uses a blower kit to assist in
air circulation.
Direct Vent An appliance that draws combustion air from outdoors and exhausts its combustion products to the outdoors,
eliminating the need for a standard chimney system. The glass panel in direct vent units keeps the combustion
system sealed from the home, maintaining high efficiency and indoor air quality.
Gas Fireplace Insert A gas appliance designed for installation within an existing fireplace. Usually this consists of gas logs within a metal
enclosure surrounding the logs and covering the space between the insert and the fireplace opening.
Mechanical A firebox that vents combustion by-products horizontally through the wall with an electric fan. This configuration
Sidewall Vent is commonly referred to as direct vent, but termination conditions differ.
Top-Vent A vented appliance that is primarily aesthetic, with lower heat efficiency than other types of fireboxes. Top-vent
inserts include standard masonry chimneys and non-masonry flues placed above the firebox.
Vent-Free or Ventless A gas appliance with no need for a flue. Although these units offer high efficiency, some areas may not permit their
use. Review local building codes before installation.
For clarification, a zero-clearance fireplace is any firebox with associated ornamentation directly adjacent to it
without clearance or setbacks.
Firebox and Insert Knowledge
5 Casting Fireplace Surrounds