Direct Venting; Removal Of Existing Furnaces From Common Vent Systems; Combustion-Air And Vent Piping - Carrier 58MVP Installation, Start-Up, And Operating Instructions Manual

control. (See Fig. 27 and 28.) When a dehumidify demand
exists, relay is de-energized, and normally closed contacts
supply 24v to the furnace DEHUM terminal. As a result, the
furnace control reduces the blower airflow by 15 percent to
340 CFM per ton during continuous fan or cooling operation.
On newer style variable speed furnace controls a field supplied
relay IS NOT required. The DEHUM output on the thermi-
distat control or the humidistat output is connected directly to
the DEHUM terminal on the furnace control. In addition, the
DE jumper located next to the DEHUM terminal must be
removed to enable the DEHUM input. (See Fig. 27 and 29.)
When a dehumidify demand exists, the furnace control re-
duces the blower airflow by 21 percent to 315 CFM per ton
during continuous fan or cooling operation.
THERMIDISTAT
R
24 VAC HOT
DEHUMIDIFY DHUM
24 VAC COMM C
→ Fig. 28—Without DE Connection
THERMIDISTAT
R
24 VAC HOT
DEHUMIDIFY DHUM
24 VAC COMM C
→ Fig. 29—With DE Connection

DIRECT VENTING

The 58MVP Furnaces require a dedicated (one 58MVP furnace
only) direct-vent system. In a direct-vent system, all air for
combustion is taken directly from outside atmosphere, and all flue
products are discharged to outside atmosphere.
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:
VARIABLE-SPEED
CONDENSING
FURNACE
R
DEHUM
Com
A98294
VARIABLE-SPEED
CONDENSING
FURNACE
R
DEHUM
DE
NOTE 1
Com
NOTE 1 - Remove DE Connection
To Enable DEHUM Input
A98295
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-
1996/ANSI Z223.1-1996 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
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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). 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. 30.) 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.
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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.
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