Comfortaire Century GDD80C User manual

506843-01 Page 1 of 39Issue 1132
This is a safety alert symbol and should never be ignored. When you see this symbol on labels or in
manuals, be alert to the potential for personal injury or death.
As with any mechanical equipment, personal injury can
result from contact with sharp sheet metal edges. Be
careful when you handle this equipment.
CAUTION
Improper installation, adjustment, alteration, service or
maintenance can cause property damage, personal injury
or loss of life. Installation and service must be performed
by a licensed professional installer (or equivalent), service
agency or the gas supplier.
WARNING
This manual must be left with the homeowner for future reference.
INSTALLATION INSTRUCTIONS
GDD80C
Warm Air Gas Furnace
Downflow Air Discharge
(P) 506843-01
*P506843-01*
Unit Dimensions .............................................................. 2
GDD80C PartsArrangement ................................................ 3
GDD80C Gas Furnace ......................................................... 4
Shipping and Packing List ............................................... 4
Safety Information .......................................................... 4
Use of Furnace as a Construction Heater ....................... 5
General .......................................................................... 6
Combustion, Dilution, Ventilation Air ................................. 6
Setting Equipment ........................................................... 9
Filters ........................................................................... 12
Duct System ................................................................. 12
Venting ......................................................................... 12
Gas Piping .................................................................... 21
TABLE OF CONTENTS
Electrical ..................................................................... 22
Unit Start-Up ............................................................... 27
Heating Sequence of Operation ................................. 28
Gas Pressure Adjustment ........................................... 28
Control Settings .......................................................... 28
High Altitude ................................................................ 29
Other Unit Adjustments .............................................. 29
Blower Performance .................................................... 31
Service ........................................................................ 32
Planned Service ........................................................... 35
Control Diagnostic Codes .............................................. 35
Repair Parts List ........................................................... 36
Start-Up Check List ....................................................... 37
Manufactured By
Comfort-Aire / Century
1900 Wellworth Ave.
Jackson, MI 49203

506843-01Page 2 of 39 Issue 1132
GDD80C Unit Dimensions - inches (mm)
FRONT VIEW SIDE VIEW
A
368
14-1/2
Model
GDD80C
BC
in. mm in. mm in. mm
340
13-3/8 330
13
533
21 504 19-7/8 495
19-1/2
D
in. mm
203
8
121
4-3/4
070B3
090B4
110C5
045A3
446
17-1/2 416
16-3/8 406
16 159
6-1/4

506843-01 Page 3 of 39Issue 1132
Expanded View
Figure 1
BLOWER ASSEMBLY
CABINET
CONTROL BOX
INTERNAL FLUE
PIPE ASSEMBLY
FLUE CHASE
HEAT EXCHANGER
GAS VALVE
ACCESS PANEL
BURNER BOX ASSEMBLY
COMBUSTION AIR INDUCER

506843-01Page 4 of 39 Issue 1132
GDD80C Gas Furnace
The GDD80C gas furnace is shipped ready for
installation in the downflow position.
The furnace is equipped for installation in natural gas
applications. Aconversion kit (ordered separately) is required
for use in propane/LP gas applications.
This unit can be installed as either a Direct Vent or a
Non-Direct Vent gas central furnace
NOTE: In Direct Vent installations, combustion air is taken
from outdoors and flue gases are discharged outdoors. In
Non-Direct Vent installations, combustion air is taken from
indoors and flue gases are discharged outdoors.
Shipping and Packing List
1 - Assembled Gas Furnace
1 - Bag assembly containing the following:
2 - Screws
3 - Wire nuts
1 - Snap bushing
1 - Snap Plug
1 - Wire tie
1 - Vent warning label
1 - Owner’s manual and warranty card
Check equipment for shipping damage. If you find any
damage, immediately contact the last carrier.
Please refer to the technical specification sheets for available
accessories.
Safety Information
As with any mechanical equipment, personal injury can
result from contact with sharp sheet metal edges. Be
careful when you handle this equipment.
CAUTION
DANGER OF EXPLOSION!
DANGER
There are circumstances in which odorant used with LP/
Propane gas can lose its scent. In case of a leak, LP/
Propane gas will settle close to the floor and may be difficult
to smell. An LP/Propane leak detector should be installed
in all LP applications.
Improper installation, adjustment, alteration, service or
maintenance can cause property damage, personal injury
or loss of life. Installation and service must be performed
by a licensed professional installer (or equivalent), service
agency or the gas supplier.
WARNING
Certifications
These units are CSA International certified to ANSI Z21.47.
In the USA, installation of gas furnaces must conform with
local building codes. In the absence of local codes, units
must be installed according to the current National Fuel Gas
Code (ANSI-Z223.1). The National Fuel Gas Code is
available from the following address: American National
Standards Institute, Inc., 11 West 42nd Street, New York,
NY 10036.
Clearances
Adequate clearance must be made around the air openings
into the vestibule area. In order to ensure proper unit
operation, combustion and ventilation air supply must be
provided according to the current National Fuel Gas Code.
Vent installations must be consistent with the venting tables
(in this instruction) and applicable provisions of local building
codes.
This furnace is CSA International certified for installation
clearances to combustible material as listed on the unit
nameplate and in the tables in figures 8 and 10. Accessibility
and service clearances must take precedence over fire
protection clearances.
NOTE: For installation on combustible floors, the furnace
shall not be installed directly on carpeting, tile, or other
combustible material other than wood flooring.
Installed Locations
For installation in a residential garage, the furnace must be
installed so that the burner(s) and the ignition source are
located no less than 18 inches (457 mm) above the floor.
The furnace must be located or protected to avoid physical
damage by vehicles. When a furnace is installed in a public
garage, hangar, or other building that has a hazardous
atmosphere, the furnace must be installed according to
recommended good practice requirements and current
National Fuel Gas Code.

506843-01 Page 5 of 39Issue 1132
Temperature Rise
NOTE: Furnace must be adjusted to obtain a temperature
rise within the range specified on the unit nameplate. Failure
to do so may cause erratic limit operation and may result in
premature heat exchanger failure.
This furnace must be installed so that its electrical
components are protected from water.
Installed in Combination with a Cooling Coil
When this furnace is used with cooling units, it shall be
installed in parallel with, or on the upstream side of, cooling
units to avoid condensation in the heating compartment. See
Figure 2. With a parallel flow arrangement, a damper (or
other means to control the flow of air) must adequately
prevent chilled air from entering the furnace. If the damper
is manually operated, it must be equipped to prevent
operation of either the heating or the cooling unit, unless it
is in the full HEAT or COOL setting. See Figure 2.
This furnace may be installed in alcoves, closets, attics,
basements, garages, and utility rooms in the upflow or
horizontal position.
This furnace design has not been certified for installation in
mobile homes, recreational vehicles, or outdoors.
Use of Furnace as a Construction Heater
These units are not recommended for construction heating
during any phase of construction. Very low return air
temperature, harmful vapors and operation of the unit with
clogged or misplaced filters will damage the unit.
These units may be used for heating of buildings or structures
under construction, if the following conditions are met:
•The vent system must be permanently installed per these
installation instructions.
•A room thermostat must control the furnace. The use
of fixed jumpers that will provide continuous heating is
not allowed.
•The return air duct must be provided and sealed to the
furnace.
•Return air temperature range between 60°F (16°C) and
80°F (27°C) must be maintained.
•Air filters must be installed in the system and must be
maintained during construction.
•Air filters must be replaced upon construction
completion.
•The input rate and temperature rise must be set per the
furnace rating plate.
•One hundred percent (100%) outdoor air must be
provided for combustion air requirements during
construction. Temporary ducting may supply outdoor
air to the furnace. Do not connect duct directly to the
furnace. Size the temporary duct following these
instructions in section for Combustion, Dilution and
Ventilation Air in a confined space with air from outside.
•The furnace heat exchanger, components, duct system,
air filters and evaporator coils must be thoroughly
cleaned following final construction clean-up.
•All furnace operating conditions (including ignition, input
rate, temperature rise and venting) must be verified
according to these installation instructions.
When installed, this furnace must be electrically grounded
according to local codes. In addition, in the United States,
installation must conform with the current National Electric
Code, ANSI/NFPA No. 70. The National Electric Code (ANSI/
NFPA No. 70) is available from the following address:
National Fire Protection Association
1 Battery March Park
Quincy, MA 02269
NOTE: This furnace is designed for a minimum continuous
return air temperature of 60° F (16°C) or an intermittent
operation down to 55° F (13°C) dry bulb for cases where a
night setback thermostat is used. Return air temperature
must not exceed 85° F (29°C) dry bulb.
Figure 2
Heating Unit Installed Parallel to Air Handler Unit