Category I Venting is venting at a non-positive pressure. A
furnace vented as Category I is considered a fan-assisted
appliance and does not have to be “gas tight.” NOTE: Two
stage gas furnaces with induced draft blowers draw prod-
ucts of combustion through a heat exchanger allowing in
some instances common venting with natural draft appli-
ances (i.e. water heaters).
All installations must be vented in accordance with National
Fuel Gas Code NFPA 54/ANSI Z223.1 - latest edition. In
Canada, the furnaces must be vented in accordance with
the National Standard of Canada, CAN/CSA B149 - latest
additions and amendments.
NOTE: The vertical height of the Category I venting system
will be at least as great as the horizontal length of the venting
system.
WARNING
To prevent possible death or personal injury
due to asphyxiation, common venting with
other manufacturer’s induced draft
appliances is not allowed.
The minimum vent diameter for the Category I venting
system is as shown below:
MINIMUM VENT DIAMETER
MODEL
GUIS
GCIS
70
4 Inch
4 Inch
90
4 Inch
4 Inch
115
5 Inch
N/A
140
5 Inch
N/A
Under some conditions, larger vents than those shown
above may be required or allowed.
When an existing furnace is removed from a venting system
serving other appliances, the venting system may be too
large to properly vent the remaining attached appliances.
The following steps shall be followed with each appliance
remaining connected to the common venting system placed
in operation, while the other appliances remaining con-
nected to the common venting system are not in operation.
(a) Seal any unused openings in the common venting
system.
(b) Visually inspect the venting system for proper size and
horizontal pitch as required in the National Fuel Gas
Code NFPA 54/ANSI Z223.1, or the CAN/CSA B149
Installation Codes and these instructions. Determine
there is no blockage or restriction, leakage, corrosion or
other deficiencies which could cause an unsafe condi-
tion.
(c) Where practical, close all building doors, windows, and
all doors between the space where the appliances
remain connected to the common venting system are
located and other spaces of the building. Turn on all gas
appliances not connected to the common venting sys-
tem and operate on high speed all exhaust fans (range
hoods and bathroom), except summer exhaust fans.
Close fireplace dampers.
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