6
CLEARANCES
Under no circumstances should
combustible material be located within the
clearances specifi ed in Table 3. Failure to provide
proper clearance could result in personal injury
or equipment damage from fi re.
Maintain adequate clearances around air openings into
the combustion chamber:
Table 3 - Minimum Clearances
Sides
18"
(457mm)
Top
6"
(152mm)
Bottom
25"
(635mm)
Flue
6"
(152mm)
* When clearances required for accessibility are greater
than the minimum required safety clearances, the
accessibility clearances take precedence.
NOTICE: Increasing the clearance distances may be
necessary if there is a possibility of distortion or
discoloration of adjacent materials.
Atmospheres containing commercial solvents or
chlorinated hydrocarbons will produce corrosive acids
when coming in contact with the fl ames. This will greatly
reduce the life of the duct furnace, and may void the
warranty. Avoid such areas.
NOTICE: If the gas duct furnace is to be used in a
building classified as having a hazardous
atmosphere, the installation must comply with the
standards set by the National Board of Fire
Underwriters. Consult the authorities having
jurisdiction before starting the job.
The Separated Combustion Duct Furnace must be
installed on the positive pressure side of the air circulation
blower.
INSTALLATION
NOTICE: Furnace sizing should be based on heat loss
calculations where the furnace output equals or
exceeds heat loss.
Do not install duct furnaces in a
corrosive or flammable atmosphere! Premature
failure of, or severe damage to the unit will result!
Duct furnaces must not be installed in
locations where air for combustion would contain
chlorinated, halogenated, or acidic vapors. If located
in such an environment, premature failure of the unit
will occur!
ACCESSIBILITY: The Separated Combustion Duct
Furnace is a bottom service access type. Allow a minimum
of 25 inches (635mm) at the bottom of the unit to facilitate
servicing the burners and pilot. Provision should be made
to assure accessibility for recurrent maintenance
purposes.
AIRCRAFT HANGARS: Separated Combustion Duct
Furnaces must be installed in aircraft hangars as follows:
Duct furnaces must be at least 10 feet (3.05m) above the
upper surface of wings or engine enclosures of the highest
aircraft to be stored in the hangar, and 8 feet (2.44m)
above the fl oor in shops, offi ces, and other sections of
the hangar where aircraft are not stored or housed. In
Canada, installation is suitable in aircraft hangars when
acceptable to the enforcing authorities.
PUBLIC GARAGES: In repair garages, duct furnaces
must be installed in a detached building or room separated
from repair areas as specifi ed in the latest edition of NFPA
88B, Repair Garages.
In parking structures, duct furnaces must be installed so
that the burner fl ames are located a minimum of 18 inches
(457mm) above the fl oor or protected by a partion not
less than 18 inches (457mm) high. Refer to the latest
edition of NFPA 88A, Parking Structures.
In Canada, installation must be in accordance with the
latest edition of CGA B149 “Installation Codes for Gas
Burning Appliances and Equipment.”
Separated Combustion Duct Furnaces should not be
installed to maintain low temperatures and/or freeze
protection of buildings. A minimum of 50°F (10°C)
thermostat setting must be maintained. If duct furnaces
are operated to maintain lower than 50°F (10°C), hot fl ue
gases are cooled inside the heat exchanger to the point
where water condenses onto the heat exchanger walls. The
result is a mildly corrosive acid which prematurely corrodes
the aluminized heat exchanger, and can actually drip water
down from the duct furnace onto the floor surface.
Additional duct furnaces should be installed if a minimum
of 50°F (10°C) thermostat setting cannot be maintained.
DUCTWORK: Properly designed and installed ductwork,
providing a uniformly distributed fl ow of air across the
surfaces of the heat exchanger, is essential to satisfactory
unit performance and life of the equipment.
All duct fl anges/seams must be sealed to prevent air leaks.
Sealant/tape must be suitable for temperatures of 250°F
(121°C) minimum.
Any attempt to straighten the 90°
duct connection fl anges on the duct furnace will
affect the operation of the furnace and void the
warranty.
