There are three basic types of chimneys: single-walled metal; masonry; and
pre-fabricated metal, often referred to as factory-built.
For residential use, they are generally used to remove the exhaust from
fireplaces, water heaters, and heating systems.
Single-walled metal chimneys should not be confused with factory-built metal
ones, and are rarely found in residential use, but masonry and factory-built
chimneys are commonplace. Lined masonry chimneys are the most dependable because the flue
liner not only provides a smooth transition for the bi-products
of combustion to be vented beyond the residence, but provides an
approved thermal barrier as well. Unlined chimneys, or those without flue liners, are suspect.
Although such flues include a plaster coat of mortar, the corrosive
effect of flue gases and the elements can deteriorate the mortar.
In fact, the
Chimney
Safety Institute of America
reported in 1992
that "all unlined chimneys, irrespective of fuel used, are very
liable to become defective through disintegration of the mortar
joints." There are a wide variety of pre-fabricated chimneys, which are constructed
on site with approved components.
Because portions of them cannot be viewed without dismantling the chimney,
we cannot guarantee that any particular component is the one stipulated for
use by the manufacturer. Our inspection of chimneys is that of a generalist. We are limited in our
scope to those areas that can be viewed without dismantling any portion of
chimney and does not require the use of specialized equipment.
The Chimney Safety Institute of America
has documented that significant areas of chimney flues cannot be
adequately viewed during a field inspection even with a strong light.
So although your NAHIPA Member Home Inspector will report on the general
condition of the chimney, we can not guarantee its integrity or
drafting ability and recommend that they be examined by a specialist. | 
