Specifications

5
Problem Description Can Occur when.. Possible Solutions
The chimney ue is too
small.
A chimney may be
severely restricted if the
inner diameter of the ue
is too small. The velocity of
the ue gas reaches a point
where the ow resistance
is so substantial that the
ow resistance exceeds the
draft.
See also “Oversized
Fireplace Opening”.
• A chimney is relined and
the diameter thus reduced.
• A one-sided replace is
converted into a
see-through replace.
• The chimney is improperly
designed (undersized) to
begin with.
• An existing chimney is
used for a heating appliance
it was not designed for.
• Redesign and rebuild the
chimney to meet the draft
requirements.
• Install a heating
appliance that does not
exceed the capacity of the
existing chimney.
• Close off one side of a
see-through replace
• Reduce the opening of the
replace. (Installing glass
doors will not help unless
the glass doors are
designed to be closed dur-
ing replace operation)
•Install a mechanical
venting system
The chimney ue is too
large.
While increasing the ue
size increases the capacity
of a chimney, it can
potentially reduce the
available draft. Gases move
more slowly in a large ue,
and a large ue has more
thermal mass (and more
surface area) than a small
ue. More heat is
transferred from the ue
gas to the chimney, which
adversely affects the draft.
Extreme cooling of the
chimney can offset gains
in capacity (see also “The
chimney is installed on an
outside wall”)
• Stove or replace insert is
connected into an existing
chimney that previously
served a wood-burning
replace.
• A wood-burning replace
is converted into a gas-red
replace and the existing
chimney is used.
• A set of gas logs is in-
stalled in a wood-burning
replace.
• The chimney is improperly
designed to begin with.
• Reline the chimney to
reduce the ue opening and
match the requirements of
the appliance it serves.
• Convert the gas-replace
back to its original
wood-burning design.
• Install a mechanical
venting system
The chimney is too short A tall chimney creates more
draft than a short chimney.
Chimney height and the
difference between ue gas
and the temperature of the
outside air are major factors
which inuence the amount
of draft. A rule of thumb for
minimum height is a total
system height (from bottom
of appliance to the top of
the chimney) of not less
than 15’. If the chimney is
too short, it could also lead
to improper termination. The
termination should
generally be at least 3 feet
above anything within 10
feet of the chimney.
• The chimney is on a
slanted roof
• The chimney is improperly
designed to begin with.
• Extend the chimney by
adding chimney sections or
tiles. If a system meets the
recommended minimum
height and draft problems
are experienced, extending
the chimney height may or
may not have an effect. Try
with a temporarily installed
chimney pipe or steel pipe
to verify this will in fact solve
the problem.
• Install a mechanical vent-
ing system
2.1.1. Problems associated with the venting system