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Notice to Home Owner
This furnace is equipped with safety devices that protect
you and your property. If one or more of these devices is
activated, furnace operation will stop. If your home is left
unattended for an extended period of time, equipment op
eration must be checked periodically. If this is not possible,
the water supply to the house should be shut off and the
pipes should be drained. This will prevent problems
associated with a NO HEAT condition (frozen pipes, etc.)
Combustion and Ventilation Air
Homes built with energy conservation in mind use tight
construction practices. These houses are sealed so well
that it becomes necessary to provide a means of bringing
in air from outside for combustion. Also, exhaust fans, ap
pliance vents, chimneys and fireplaces force additional air
that could be used for combustion out of the house. Unless
outside air is brought into the home for combustion, nega
tive 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 situation. Ne
gative pressure may also interfere with proper combus
tion, causing sooting within the heat exchanger.
The importance of the previous paragraph cannot be over
stated. Users may inadvertently block fresh air intakes af
ter 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 com
bustion 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 resulting in rust
ing and premature heat exchanger failure. It can also
cause property damage.
All oil‐fired appliances require air to be used for the com
bustion process. If sufficient amounts of combustion air
are not available, the furnace or other appliance will oper
ate in an inefficient and unsafe manner. Enough air must
be provided to meet the needs of all fuel‐burning ap
pliances, as well as appliances 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 incomplete 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 cubic
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 outdoor 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 procedures outlined for
using air from the outside for combustion and ventilation.
Confined Space
A confined space is an area with volume less than 50 cubic
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 termi
nate outside the space containing the furnace. This is es
pecially important when the furnace is mounted on a plat
form in a confined space such as a closet or small
equipment room. Even a small leak around the base of the
unit at the platform or at the return air duct connection can
cause a potentially dangerous negative pressure condi
tion. Air for combustion and ventilation can be brought into
the confined space either from inside the building or from
outside.
Air from an Adjacent Space
If the confined space housing the furnace adjoins space
categorized as unconfined, air can be brought in by provid
ing two permanent openings between the two spaces.
Each opening must have a minimum free area of 1 square
inch
(6.4 square centimeters) per 1,000 Btu (293 W) per
hour of the total input rating of all fuel‐fired equipment in the
confined space. Each opening must be at least 100 square
inches (614.5 square centimeters). One opening shall be
within 12” (305 mm) of the top of the enclosure and one
opening within 12” (305 mm) of the bottom (See figure 4).
