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In general, a short masonry chimney on the exterior of the
house will give the poorest performance. This is because
it can be very difficult to warm up, and in extremely cold
northern areas it may not work at all.
A tall masonry chimney inside the house is easier to keep
warm and will work best.
This guideline gives the necessary chimney requirements
based on the U.S. national code (NFPA-211). However, many
local codes differ from the national code to take into
account climate, altitude, or other factors. It is important
that you check with your local building officials to find
out what codes apply in your area before constructing a
chimney.
Masonry Chimneys
The minimum requirements for a properly constructed
chimney include the following:
• The foundation must be large enough to support the
intended chimney without settling.
• The masonry wall of the chimney, if brick or modular
block, must be a minimum of 4" nominal thickness. A
mountain- or rubble-stone wall must be at least 12" thick.
• The chimney must have a fireclay flue liner (or
equivalent with a minimum thickness of 5/8" and must
be installed with refractory mortar. There must be at1/2"
air space between the flue liner and chimney wall.
• The preferred fireclay flue liner size has a nominal size
of 8" x 8", and should not be larger than 8" x12". lf round
fireclay liners are used, the inside diameter should
be 6" and not larger than 8". lf an existing chimney
with larger tiles is used it should be relined with an
appropriate liner.
• No other appliance can be vented into the same flue.
• An airtight cleanout door should be located at the base
of the chimney.
A chimney inside the house must have at least 2" of
clearance to the combustible structure. A chimney
outside the house must have at least 1" clearance to the
combustible structure. Fire stops must be installed at the
spaces where the chimney passes through floors and/or
ceilings. Remember that there must be air space around
the chimney, and that insulation must be 2" or more from
the chimney.
A chimney, wether masonry or prefabricated metal, must
be the required height above the roof or other obstruction
for safety and for proper draft operation. The requirement
is that the chimney must at least 3' higher than the highest
point where it passes through the roof and at least 2'
higher than the be at least and highest part of the roof
or structure that is within 10' of the chimney, measured
horizontally (fig. 4, page 23.
Chimneys shorter than 14' may not provide adequate draft.
This could result in smoke spilling the room from the door
or joints in the stove or pipe. In addition, inadequate draft
can cause puffing. A too-strong draft, on the other hand,
cause excessive temperatures and can shorten burn times.
Excessive drafts can be corrected by having your dealer
install a barometric damper at 0.1 " of water column. lf you
suspect you have draft problem, consult your dealer.
Listed Metal Prefabricated Chimneys
The heater must be connected to a listed Type HT per
UL 103 or ULC S629 prefabricated chimney. When a
metal prefabricated chimney is used, the manufacturer's
installation instructions must be followed precisely. You
must also purchase (from the same manufacturer) and
install the ceiling support package or wall pass through,
the "T" section package, the firestops (when needed),
the insulation shield, the roof flashing, the chimney
cap, etc. Maintain the proper clearance to the structure
as recommended by the manufacturer. This clearance
is usually a minimum of 2", although it may vary by
manufacturer or for certain components.
There are basically two methods of metal chimney
installation. One method is to install the chimney inside
the residence through the ceiling and the roof (fig. 5,
page 24).
The other method is to install an exterior chimney that
runs up the outside of the residence.
USA
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