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Technical Aspects of Chimney
Performance
A device called a manometer is used in
measuring 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 9lled 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 dra; in the
chimney should exert enough pressure (or pull)
against the water in the manometer to cause it to
move at least -.04 inches in the tube. For units to be
operated on coal, limit maximum dra; to -.08 inches.
Use of a barometric damper may be required.
Dwyer Manometer
To measure the dra;, drill a hole in the connector
pipe and a=ach a dra; meter or manometer. First,
check the dra; above the barometric damper (if
installed).
en check it below the barometric
damper and make your damper adjustment to where
it opens to prevent the dra; from going higher than
-.08 inches of water column. If the chimney is
incapable of supplying the required dra;, it will
need to be improved. See the section on Common
Chimney Problems for more information.
Barometric Damper
A barometric damper is a device that allows room
air to enter the chimney, bypassing the air intake on
the heater. A heater and chimney combination that
dra;s well will occasionally produce more dra; than
is desired. Excessive dra; can lead to burning out of
control and excessive heat production. It will also
lead to reduced e:ciency, as more heat will end up
going up the chimney. A barometric damper is used
on a coal 9red heater to limit maximum dra; to -.08
column inches.
e barometric damper needs to be
the same diameter as the stove collar. It is to be
installed in the chimney connecting pipe as shown
below, utilizing a Tee in the stove pipe.
It is important to check the chimney dra; when
the seasons change to ensure dra; se=ings are
correct. Changes may be needed when transitioning
from winter heating to summer heating (domestic
water heating).
from one season to the next. It is not uncommon to
add a dra; inducer in warmer seasons to maintain
the recommended -.04 to -.07 inches of water
column.
Barometric Damper
Combustion Air (Make Up Air)
e airEow through the system and out the
chimney means that oxygen is leaving the home and
will create an oxygen de9cit if this air is not
replaced. Adequate combustion air is critical for the
performance of your heater.
su:cient leakage in older homes to provide for this,
but in well-insulated homes it may be necessary to
provide additional outside air into the home.
Combustion air can be provided with a duct to the
outside. A louvered vent can also be used.
- 3 -
e amount of dra; will change
ere is usually
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