Gas Furnace Identification; Gas-Fired Duct Furnaces - Carrier AERO 39MN Installation, Start-Up And Service Instructions Manual

Gas Furnace Identification —
sections of 39M air-handling units offer two styles of gas fur-
nace: the gas-fired duct furnace and the gas-fired rack system.
Air-handling units with the duct heater can have 1 or 2 gas sec-
tions with a single duct furnace in each section. Air-handling
units with the rack system can have 1 or 2 gas sections with 1 to
5 racks in each section (up to 10 racks total).
To determine the type of gas heating system in the air-han-
dling unit, open the burner side door to view the burner assem-
bly. Gas-fired duct furnaces have the burners arranged vertically.
See Fig. 93. Rack system furnaces have the burners arranged
horizontally. See Fig. 94.
BURNERS
Fig. 93 — Gas-Fired Duct Furnace Burner Assembly
Fig. 94 — Gas-Fired Rack System Burner Assembly
Follow the appropriate installation instructions below for the
style of gas furnace included in the air-handling unit.
The gas heat section or
a39-4406
a39-
4405
BURNERS

Gas-Fired Duct Furnaces

IMPORTANT: This furnace is not listed or suitable
for drying or process applications. Use in such appli-
cations voids any warranty and manufacturer dis-
claims any responsibility for the duct furnace and/or
application.
INSTALLATION REQUIREMENTS — Gas-fired duct fur-
naces are factory installed. If circumstances require field instal-
lation of a gas furnace, it can only be installed in a factory-
supplied gas heater section. All unit installations must be in
accordance with the National Fuel Gas Code ANSI Z223.1
(NFPA 54) in the United States and Can/CGA-B149 Installation
Code in Canada, and all other applicable local codes and ordi-
nances. These requirements include but are not limited to:
• Combustion air supply to the heating equipment
• Venting of the products of combustion (flue gases)
• Gas supply, piping and connections
• Unit location and clearances
All electrical equipment must be grounded and wired in accor-
dance with the National Electric Code (ANSI/NFPA 70) in the
United States, and the Canadian Electric Code (CSA C22.1), in
Canada.
VERIFICATION — Verify the following before placing the
equipment into service:
• Electrical supply matches the heater voltage marked on the
duct furnace Rating Plate.
• Gas supply provided matches the Gas Type marked on the
duct furnace Rating Plate.
• Furnace is installed in orientation marked on vestibule. Ori-
entation is specific to airflow direction through the heating
section of the unit.
• There is an adequate supply of fresh air for the combustion
and ventilation process. Combustion air openings in the cabi-
net should be sized to provide 1 sq in. of free area per 4000
Btuh of input.
The presence of chlorine vapors in the combustion air sup-
plied to gas-fired heaters presents a substantial corrosion
hazard.
• A properly designed vent system is connected to the heating
unit to convey the products of combustion (flue gases) out-
side the building. For outdoor applications be sure the flue
gases are directed away from any combustion air inlets.
• Duct furnace assembly is installed in a non-combustible duct
or cabinet on the positive pressure side of the circulating air
blower.
• An air flow proving switch is installed and wired to prove
operation of the system circulating air blower.
• An auxiliary manual reset limit switch is installed to shut off
furnace in the event of low airflow conditions due to filter
blockage, coil blockage and or damper failure.
• A drain tube is installed for disposal of condensate, if the
heating unit is equipped with modulating controls or is
located downstream of cooling system.
• Equipment access panels and doors are sized and located to
provide easy access for servicing, adjustment and mainte-
nance of the heating units installed.
111
CAUTION