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, NFPA 54-
1999/ANSI Z223.1-1999 or the CAN/CGA B149 Installation
Codes and these instructions. Determine that there is no
blockage or restriction, leakage, corrosion, and other deficien-
cies which could cause an unsafe condition.
3. If 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
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),
F891 (PVC-DWV cellular core) or F441 (schedule-40 CPVC pipe)
and F438 (schedule -40 CPVC fittings). Pipe cement and primer
must conform to ASTM standards D2564 or F493 (PVC or CPVC)
D2235 (ABS). See Table 6 for maximum pipe lengths and Fig. 34,
35, 36, 37, and 38 for exterior piping arrangements.
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.
NOTE: Furnace combustion-air and vent pipe connections are
sized for 2-in. pipe. Any pipe size change should be made outside
furnace casing in vertical pipe. (See Fig. 29.) This allows proper
drainage of vent condensate.
Combustion-air and vent pipes must terminate together in same
atmosphere pressure zone, either through roof or sidewall (roof
termination preferred), using accessory termination kit. See Table
5 for required clearances.
Furnace combustion-air and vent pipe connections must be at-
tached as shown in Fig. 31. Combustion-air intake plug fitting and
inducer housing alternate vent cap may need to be relocated in
some applications.
NOTE: →Slope combustion-air and vent pipes a minimum of 1/4
in. per linear ft with no sags between hangers.
Fig. 28—Thermidistat Connection
A98295
24 VAC HOT
DEHUMIDIFY
24 VAC COMM
RR
Com
DHUM
DEHUM
C
DE
NOTE 1
THERMIDISTAT
VARIABLE-SPEED
CONDENSING
FURNACE
NOTE 1 - Remove DE Connection
To Enable DEHUM Input
Table 5—Combustion-Air and Vent Pipe
Termination Clearances
LOCATION
CLEARANCE (FT)
U.S.A. Canada
Above grade level or above antici-
pated snow depth
11†
Dryer vent 33
From plumbing vent stack 33
From any mechanical fresh air intake 16
For furnaces with an input capacity
less than 100,000 Btuh—from any non-
mechanical air supply (windows or
doors which can be opened) or
combustion-air opening
11
From service regulator vent, electric
and gas meters, and relief equipment
4* 6‡
Above grade when adjacent to public
walkway
Note 3 Note 3
* Horizontal distance.
† 18 in. above roof surface in Canada.
‡ 36 in. to electric meter in Canada only.
NOTES:
1. If installing 2 adjacent 58MVP Furnaces, refer to Multiventing
and Vent Terminations section for proper vent configurations.
2. When locating combustion-air and vent terminations, consid-
eration must be given to prevailing winds, location, and other
conditions which may cause recirculation of the appliance’s
own flue products or the flue products of adjacent vents.
Recirculation can cause poor combustion, inlet condensate
problems, and accelerated corrosion of heat exchangers.
3. Vent termination can not terminate less than 2 ft horizontal
and 7 ft above public walkway or where condensate vapor or
droplets may be a hazard.
23
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