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Vent or
Chimney
Furnace
Water Heater
Ventilation Louvers for
unheated crawl space
Figure 10. Equipment in a Confined Space with All
Combustion Air Drawn from a
Crawl Space and Ventilated Attic
If the unit is installed in an area with an exhaust fan, provide
sufficient ventilation to prevent negative pressures from
occurring in the room.
The combustion air openings must not be restricted in any
manner.
VENTING REQUIREMENTS
General
This furnace must be vented in compliance with, the current
revision of the National Fuel Gas Code (ANSI-Z223.1/
NFPA54), with the instructions provided below.
In Canada, venting shall conform to the requirements of the
current (CAN/CGA B149.1 or .2) installation codes. Consult
local codes for special requirements.
This furnace must never be vented to a chimney flue
servicing a fireplace or other appliance designed to burn
solid fuel. If the furnace vent is to be connected to a
chimney serving a fireplace, the fireplace must be sealed
off from the chimney.
For Category I furnace installations, the furnace shall be
connected to a factory built chimney or vent complying with
a recognized standard, or a masonry or concrete chimney
lined with a lining material acceptable to the authority
having jurisdiction. Venting into an unlined masonry
chimney or concrete chimney is prohibited.
The furnace vent, if metal, may be insulated if local codes
allow. Any part of the vent system, metal vent only, not
exposed to weather, but which are exposed to ambient
temperatures below 35° F must be insulated to prevent
condensation. All vent insulation shall be foil backed
fiberglass of one inch minimum thickness.
Three sheet metal fasteners (field supplied) should be used
to secure the vent pipe to the furnace flue. These fasteners
Ventilation Louvers at
each end of attic
Outlet Air Duct
must be at least
1 sq. in. per 4000
Btuh of total input
rating. Must extend
above attic insulation.
Attic Insulation
Inlet Air Duct must
be at least 1 sq. in.
per 4,000 Btuh of
total input rating.
Crawl Space
12" Max
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Furnace
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12" Max
Total Input
Rating (Btu/hr)
40,000
60,000
80,000
100,000
120,000
140,000
160,000
Figure 11. Equipment in a Confined Space with all
Combustion Air Drawn from the Outside through
Horizontal Ducts
should be evenly spaced around the flue diameter, if
possible.
Category I - Common Venting
When an existing furnace is removed from a venting system
serving other appliances, the venting system is likely to be too
large to properly vent the remaining appliances. An improperly
sized venting system can result in the formation of condensate,
leakage, spillage, etc.
The venting system should be designed to have the
minimum number of elbows or turns. All horizontal runs
shall be sloped upwards from the furnace at 1/4 inch per
running foot of vent. Supports for the vent pipe must be
installed a minimum of every five feet along the vent run to
ensure no displacement after installation.
Under no circumstances shall any portion of the vent
system extend into or pass through any return air duct,
supply air duct, or plenum.
If the furnace is operated with blocked or restricted venting,
the blocked vent switch located in the vent plate will open,
turning off the gas supply to the burners. The blocked vent
switch is a manually reset device. DO NOT install a jumper
Vent or
Chimney
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Air Duct
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Air Duct
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Water Heater
Minimum
Free Area
Round Duct
(Each Opening)
Diameter
20 sq. in.
5"
30 sq. in.
6"
40 sq. in.
7"
50 sq. in.
8"
60 sq. in.
9"
70 sq. in.
10"
80 sq. in.
10"
13
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