Site-built masonry is expensive and takes days or
weeks to build, which is why the vast majority
of new fireplaces are prefabricated, manufactured
units. A typical manufactured fireplace is
a double-wall metal box that
connects to a metal flue pipe.
Most are zero-clearance units,
which is another way of saying that they sit directly on
the subfloor and can be installed close to or in contact
with combustible framing. But most manufacturers
suggest leaving 1/2-inch clearance to the back and sides
for thermal expansion. Greater clearances are required
above the box and around the flue pipe. Fireplaces usually
require permits and must be installed to code.
The vast majority of manufactured fireplaces use