Alternate Heating COAL GUN S130, Installation And Operator'S Manual

Page: 10 / 66

Draft
Natural draE in a chimney results from several
factors. /e main characteristic of draE is lower
pressure at the top opening of the chimney than
further down. /is can be created by air currents
blowing across the top of the chimney. In addition,
draE is also produced when the temperature of the
@ue gases is higher than the atmosphere around the
chimney. /is is known as the stack eDect. A
chimney must be kept warm (about 250º F) for
proper draE to occur. A chimney's height, expressed
as the diDerence between the top opening and the
@ue pipe connection on the appliance, contributes to
draE because atmospheric pressure is naturally
lower at the chimney top than bo om. See DraE
Control section in this manual for more information.
It is more diIcult to maintain suIcient
temperature in an exposed chimney, or one that is
very large, than a chimney that is protected from
outside temperature extremes. For this reason,
insulated chimneys typically provide more draE, due
to increased stack eDect. A chimney with a large
cross-sectional area may have diIculty becoming
warm enough to produce good draE, because gases
cool too much before exiting the chimney.
/e chimney must be suIciently tall (at least 20
feet for masonry chimneys) and should extend at
least three feet above the highest part of the roof to
prevent downdraEs. /e chimney must be leak-free
from the standpoint of air entering through cracks or
other chimney defects or through loose stovepipe
1 ings.
3-2-10 Rule for Chimneys
If the chimney must go through a combustible
wall, be sure to use a metal thimble specially
designed for this purpose. /e proper way to install a
thimble is to cut an oversize hole in the sheetrock
about 6 or 7 inches larger than the thimble (refer to
Figure 2). However, be sure to follow the
manufacturer’s directions that come with the
thimble. A metal ring shield is used to cover the hole.
/is way air can circulate and cool the area around
the passageway.
Never decrease the cross-sectional area of the
stovepipe/chimney because the velocity of the
exhaust will increase thus increasing the likelihood
of particle discharge in the exhaust.
Technical Aspects
of Chimney Performance
A device called a manometer is used in
describing the technical performance of a chimney.
A manometer is an instrument used for measuring
the pressure of liquids and gases. An analog
manometer consists of a glass tube 1lled with a
liquid and mounted in front of a measuring scale
against which the liquid level can be measured. If a
manometer were connected to a leak-free chimney
with a leak-free connection, then the draE in the
chimney should exert enough pressure (or pull)
against the water in the manometer to cause it to
move at least 0.04 inches in the tube.
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NOTE: For insurance and building code
compliance check with your local building
inspector and insurance agent.