6
INSTALLATION
LOCATING UNITS
D o n o t i n s t a l l d u c t f u r n a c e s i n
corrosive or flammable atmospheres! Premature
failure of, or severe damage to the unit will result!
Avoid locations where extreme drafts
can affect burner operation. 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!
NOTICE: Location of duct furnaces is related directly
to the selection of sizes. Basic rules are as follows:
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 Safety Clearances*
Sides
6 inches (152mm)
Top
6 inches (152mm)
Bottom
6 inches (152mm)
Flue
6 inches (152mm)
* When clearances required for accessibility are greater than the
minimum safety clearances, the accessibility clearances take
precedence.
ACCESSIBILITY CLEARANCE: the duct furnace must
have 18 inches (457mm) clearance on the control cabinet
end. Provision should also be made to assure accessibility
for recurrent maintenance purposes.
ATMOSPHERIC CONSIDERATIONS: Atmospheres
containing commercial solvents or chlor inated
hydrocarbons will produce corrosive acids when coming
in contact with the fl ames. This will greatly reduce the life
of the gas duct furnace and may void the warranty. Avoid
such areas.
NOTICE: If the gas duct furnace is to be used in
a bu i l d i n g cl a s s i f i e d a s h av i n g a h a z a rd o u s
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 duct furnace must be installed on the positive
pressure side of the air circulation blower.
AIRCRAFT HANGARS: In aircraft hangars, 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 (2.4m) above
the floor in shops, offices, and other sections of the
hangar where aircraft are not stored and housed. Refer
to current ANSI/NFPA No. 409, Aircraft Hangars. 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 partition 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 CSA B149 “Installation Codes for Gas
Burning Appliances and Equipment.”
NOTICE: The duct furnace must be installed such
that the gas ignition control system is not directly
exposed to water spray, rain, or dripping water.
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 vapor (a fl ue
gas byproduct) condenses onto the heat exchanger walls.
The result is a mildly corrosive acid that prematurely
corrodes the aluminized steel heat exchanger and can
actually drip water down from the duct furnace onto the
fl oor surface below. Additional duct furnaces should be
installed if a minimum 50°F (10°C) thermostat setting
cannot be maintained.
