nections, vent pipe diameter required and submittal for
location.
Indoor Installation
Air for Combustion
Locate appliance to ensure an adequate supply of fresh
air to replace air used in the combustion and ventilation
process of the furnace module. The appliance must be
installed in a location with adequate clearances to pro-
vide for an adequate combustion air space, service and
inspection and proper clearances from combustible con-
struction. The appliance must be located in such a man-
ner that it does not interfere with the circulation of air in
the heated space.
All fuel burning equipment must be supplied with air that
enters into the combustion process and is then vented
outdoors. Sufficient air must enter the appliance location
to replace the air exhausted through the vent system. Do
not install appliance in a confined space without providing
wall openings to and from this space. If building construc-
tion is such that the normal infiltration does not provide
sufficient air for combustion and venting, outside air must
be introduced. Install air openings that provide a total free
area in accordance with following and to the National Fuel
Gas Code Z223.1 (NFPA 54) in the US or in Canada, to
the Can/CGA-B149 Installation Code:
1. Air from inside the building – Opening of 1 sq. inch
[645 mm
2
] per 1,000 Btuh [293 W] of input, but
never less than 100 sq. inch [0.06 m
2
].
2. Air from outside (ducted) – Opening of 1 sq. inch
[645 mm
2
] per 2,000 Btuh [586 W].
3. Air from outside (direct opening) – Opening of 1 sq.
inch [645 mm
2
] per 4,000 Btuh [1,172 W].
Venting
Each furnace must be connected to a venting system to
convey flue gases outside of the heated space. Refer to
installation codes noted above for specific requirements
for the product type being installed.
The induced draft fan rectangular vent connection for
each furnace is factory fitted with a rectangular to round
transition and run to the side of the furnace vestibule.
Each furnace must be connected to a separate factory
built chimney or vent complying with a recognized stan-
dard or a masonry or concrete chimney lined with a mate-
rial acceptable to the authority having jurisdiction.
The proper vent pipe diameter must be used for each
furnace to ensure proper venting of combustion products.
See Table K1 for vent pipe diameter required.
Vertically Vented Furnaces (see Figure K4) –
Category I (per NFGC and ANSI Z21.13 is a non-
condensing appliance with negative vent pressure)
1. Use single wall or double wall (Type B) vent pipe
diameters for the appropriate models. Use insulated
vent outdoors.
2. Maximize the height of the vertical run of vent pipe. A
minimum of 5 feet [1.5 m] of vertical pipe is required.
The top of the vent pipe must extend at least 2 feet
[0.61 m] above the highest point on the roof. Use
Listed Type B vent for external runs.
3. An approved weatherproof vent cap must be in-
stalled to the vent termination.
4. Horizontal runs must not exceed 75% of the vertical
height of the vent pipe, up to a maximum of 10 feet
[3 m]. Horizontal runs should be pitched upward ¼”
per foot [21 mm/m] and should be supported at 3
foot [1 m] maximum intervals.
5. Design vent pipe runs to minimize the use of elbows.
Each 90 degree elbow is equivalent to 5 feet [1.5 m]
of straight vent pipe run.
6. Vent pipe should not be run through unheated
spaces. If such runs cannot be avoided, insulate vent
pipe to prevent condensation inside vent pipe. Insula-
tion should be a minimum of ½” [12.7 mm] thick, foil
faced material suitable for temperatures up to 500°F.
7. Dampers must not be used in vent piping runs.
Spillage of flue gases into the occupied space could
result.
8. Vent connectors serving Category I heaters must not
be connected into any portion of a mechanical draft
system operating under positive pressure.
Table K1: VHC-36, -42, -50 Number of Furnace Vents,
Vent Connection Size and Vent Pipe Diameter
Input Rating
BTUH [Watts]
Number of
Furnace
Vents
Vent
Connection
Diameter
Vent Pipe
Diameter
100,000–125,000
[29,307–36,634]
1 5” [127 mm] 5” [127 mm]
200,000–400,000
[58,614–117,228]
1 6” [152 mm] 6” [152 mm]
VCES-VHC-IOM-1F – VHC-36, -42 & -50
65
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