9
Masonry Chimney
Masonry Chimneys have several positive attributes: If properly built, they are quite durable, and most homeowners
consider them more attractive perhaps than a non-enclosed factory built chimney. And, if the chimney is located
within the confines of the house (that is, not attached to an exterior wall), its mass alone will store heat longer and
continue to release the heat long after the fire has died. Masonry chimneys have many disadvantages though.
Masonry chimneys constructed on an exterior wall are exposed to cold outdoor temperatures, promoting
greater heater loss, higher accumulations of creosote, and reduced draft which leads to poorer heater or
furnace performance.
When considering a masonry chimney, round tiles are preferable to square or rectangular, as round tiles have
much better airflow characteristics and are far easier to clean. Unfortunately, most North American chimneys
use square or rectangular tile liners that are really designed for open fireplaces, not stoves or furnaces. Of most
importance, second only to overall chimney height, is the diameter of the flue liner itself. In most instances, it
should be sized to the appliance; i.e., 6” flue outlet on the appliance requires a 6” flue. The inner diameter should
never be less than the flue outlet diameter and should never be greater than 50% of the appliance flue outlet.
For example, do not expect a burning stove or furnace to function properly if installed into a chimney with a flue
liner greater than 50% the appliance outlet -- such as a 6” flue outlet requires a 6” diameter for optimum drafting,
but can function well with an 8”, but becomes borderline beyond 8” diameter.
Masonry chimneys built of concrete blocks without flue liners of at least 5/8” fireclay do not meet modern
building codes. A solid fuel appliance must not be joined to a chimney flue which is connected to another
appliance burning other fuels.
If your chimney has a typically oversized flue liner of 8x12 inches or greater, or if it is unlined, it will be necessary
for you to reline the chimney, using many of the modern approved and economical methods such as stainless
steel, castable refractory, or properly sized fireclay linings.
If you have any question regarding venting your appliance, feel free to contact the factory at the address and
phone number on this Owner’s Manual. You may also contact NFPA (National Fire Protection Association) and
request NFPA Standard 211 (1984 Edition). Their address is Battery March Park, Quincy, Massachusetts 02269.
Another helpful publication is NFPA Standard 908, available at the same address. Specify 1984 Edition on either
of the above publications.
