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Step 1—Removal of Existing Furnaces from
Common Vent Systems
If furnace being replaced was connected to a common vent system
with other appliances, the following steps shall be followed with
each appliance connected to the venting system placed in opera-
tion, while any other appliances connected to the venting system
are not in operation:
1. Seal any unused openings in the venting system.
2. Inspect the venting system for proper size and horizontal pitch
as required in the National Fuel Gas Code, ANSI Z223.1 or
the CAN/CGA B149 Installation Codes and these instructions.
Determine that there is no blockage or restriction, leakage,
corrosion, and other deficiencies which could cause an unsafe
condition.
3. In so far as is practical, close all building doors and windows
and all doors between the space in which the appliance(s)
connected to the venting system are located and other spaces
of the building. Turn on clothes dryers and any appliance not
connected to the venting system. Turn on any exhaust fans,
such as range hoods and bathroom exhausts, so they shall
operate at maximum speed. Do not operate a summer exhaust
fan. Close fireplace dampers.
4. Follow the lighting instructions. Place the appliance being
inspected in operation. Adjust thermostat so appliance shall
operate continuously.
5. Test for draft hood equipped appliance spillage at the draft
hood relief opening after 5 minutes of main burner operation.
Use the flame of a match or candle.
6. After it has been determined that each appliance connected to
the venting system properly vents when tested as outlined
above, return doors, windows, exhaust fans, fireplace damp-
ers, and any other gas-burning appliance to their previous
conditions of use.
7. If improper venting is observed during any of above tests, the
venting system must be corrected.
Vent system or vent connectors may need to be resized. For any
other appliances when resizing vent systems or vent connectors,
system or connector must be sized to approach minimum size as
determined using appropriate table found in the NFGC or NSC-
NGPIC.
Step 2—Combustion-Air and Vent Piping
GENERAL
Solvent cements are combustible. Keep away from heat,
sparks, and open flame. Use only in well-ventilated areas.
Avoid breathing in vapor or allowing contact with skin or
eyes. Failure to follow this warning could result in fire,
property damage, personal injury, or death.
Combustion-air and vent pipe fittings must conform to American
National Standards Institute (ANSI) standards and American
Society for Testing and Materials (ASTM) standards D1785
(schedule-40 PVC), D2665 (PVC-DWV), D2241 (SDR-21 and
SDR-26 PVC), D2661 (ABS-DWV), F628 (schedule-40 ABS), or
F891 (PVC-DWV cellular core). Pipe cement and primer must
conform to ASTM standards D2564 (PVC) or D2235 (ABS).
In Canada construct all combustion-air and vent pipes for this unit
of CSA or ULC certified schedule-40 PVC, PVC-DWV or
ABS-DWV pipe and pipe cement. SDR pipe is NOT approved in
Canada.
COMBUSTION AIR PIPE
Combustion air must not be taken from inside a structure that
is frequently contaminated by halogens, which include fluo-
rides, chlorides, bromides, and iodides. These elements are
found in aerosols, detergents, bleaches, cleaning solvents,
salts, air fresheners, adhesives, paint, and other household
products. Locate combustion-air inlet as far as possible from
swimming pool and swimming pool pump house.
Excessive exposure to contaminated combustion air will
result in safety and performance related problems.
NOTE: Furnace combustion-air connections are sized for 2-in.
pipe. The combustion-air pipe will be 2-in. diameter in all
installations.
Furnace combustion-air connection must be attached as shown in
Fig. 28. Combustion-air intake housing plug may need to be
relocated in some applications.
Combustion-air pipe must terminate outside of furnace casing with
1 elbow. Orient elbow so that opening faces down for upflow or
downflow applications. Orient elbow so that it faces sideways (left
or right) for horizontal left or horizontal right applications. (See
Fig. 28.) Maintain a 3-in. minimum clearance between the opening
of the combustion-air inlet pipe and any object.
NOTE:
Select 1 vent pipe connection and
1 combustion-air pipe connection.
AIR
FLOW
COMBUSTION-
COMBUSTION-
AIR
VENT
UPFLOW
COMBUSTION-
AIR
VENT
AIR
FLOW
HORIZONTAL-LEFT DISCHARGE
Make sure there is adequate clearance (3-in. minimum) to any
fixed or loose objects in order to ensure an adequate
combustion-air supply.
Fig. 28—Combustion-Air and Vent Pipe
22
NOTE:
Select 1 vent pipe connection and
1 combustion-air pipe connection.
VENT
AIR
VENT
COMBUSTION-
COMBUSTION-
AIR
AIR
FLOW
DOWNFLOW
COMBUSTION-
VENT
AIR
HORIZONTAL-RIGHT DISCHARGE
Connections
VENT
AIR
AIR
FLOW
A96188
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