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16- Where condensation of vent gas is apparent, the vent
should be repaired or replaced. Accumulation of con
densation in the vent is unacceptable.
FACTORY-BUILT CHIMNEY
BAROMETRIC
CONTROL*
(IN EITHER
LOCATION)
FACTORY
BUILT
CHIMNEY
FIGURE 10
*Barometric control may be installed in either vertical or horizontal
section of vent pipe within 18" (457 mm) of vent outlet of furnace.
17- Vent connectors serving this appliance shall not be
connected into any portion of mechanical draft sys
tems operating under positive pressure.
18- Keep the area around the vent terminal free of snow,
ice and debris.
NOTE-If vent pipe needs to exit from side of cabinet, use the
cross hairs (located on either side of the unit) to cut a 6" (152
mm) round hole. Attach finishing plate (provided) with four
sheet metal screws to cover rough edges.
Combustion and Ventilation Air
(Confined and Unconfined Spaces)
Until recently, there was no problem in bringing in suffi
cient amounts of outdoor air for combustion -- infiltration
provided all the air that was needed and then some. In
today's homes built with energy conservation in mind,
tight construction practices make it necessary to bring in
air from outside for combustion. Consideration must also be
given to the use of exhaust fans, appliance vents, chimneys
and fireplaces because they force additional air that could
be used for combustion out of the house. Unless outside
air is brought into the home for combustion, negative
pressure (pressure outside is greater than inside pres
sure) will build to the point that a down draft can occur in
the furnace vent pipe or chimney. Combustion gases enter
the living space creating a potentially dangerous situa
tion.
The importance of the previous paragraph cannot be
overstated.
Users may inadvertently block fresh air in
takes after installation.
In the absence of local codes concerning air for combus
tion and ventilation, the following section outlines guide
lines and recommends procedures for operating oil fur
naces in a manner that ensures efficient and safe
operation. Special consideration must be given to combus
tion air needs as well as requirements for exhaust vents and oil
piping.
Combustion Air Requirements
CAUTION
Insufficient combustion air can cause headaches,
nausea, dizziness or asphyxiation. It will also
cause excess water in the heat exchanger result
ing in rusting and premature heat exchanger fail
ure. It can also cause property damage.
All oil-fired appliances require air to be used for the combus
tion process. If sufficient amounts of combustion air are not
available, the furnace or other appliance will operate in an inef
ficient and unsafe manner. Enough air must be provided to
meet the needs of all fuel-burning appliances, as well as ap
pliances such as exhaust fans which force air out of the home.
When fireplaces, exhaust fans, or clothes dryers are used at
the same time as the furnace, much more air is required to
ensure proper combustion and to prevent a down-draft
situation. Insufficient amounts of air also cause incom
plete combustion which can result in sooting. Requirements
for providing air for combustion and ventilation depend largely
on whether the furnace is installed in an unconfined or
confined space.
Unconfined Space
An unconfined space is an area such as a basement or
large equipment room with a volume greater than 50 cu
bic feet (1.4 cubic meters) per 1,000 Btu (293 W) per
hour of the combined input rating of all appliances
installed in that space. This space also includes adjacent
rooms which are not separated by a door. Though an area may
appear to be unconfined, it might be necessary to bring in out
door air for combustion if the structure does not provide
enough air by infiltration. If the furnace is located in a
building of tight construction with weather stripping and
caulking around the windows and doors, follow the proce
dures outlined for using air from the outside for combus
tion and ventilation.
Confined Space
A confined space is an area with volume less than 50 cu
bic feet (1.4 cubic meters) per 1,000 Btu (293 W) per
hour of the combined input rating of all appliances
installed in that space. This definition includes furnace closets
or small equipment rooms.
When the furnace is installed so that supply ducts carry air
circulated by the furnace to areas outside the space con
taining the furnace, the return air must be handled by ducts
which are sealed to the furnace casing and which terminate
