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Other gas appliances with their own venting system may also use the abandoned chimney as a raceway providing it is permitted by local code,
the current edition of the National Fuel Gas Code and the vent or liner manufacturer’s installation instructions. Care must be taken to prevent the
exhaust gases from one appliance from contaminating the combustion air of other gas appliances.
CAUTION: When vent pipe is exposed to temperatures below freezing, such as when it passes through an unheated
space or when a chimney is used as a raceway, pipe must be insulated as shown in Table 8 with Armaflex-type insulation.
Table 5—Combustion-Air and Vent Pipe Termination Clearances
LOCATION
CLEARANCE (FT)
U.S.A. Canada
Above grade level or aboveanticipated snow depth 11†
Dryer/Water heater ventt 33
From plumbing vent stack 33
From any mechanical fresh air intake See note 4 6
For furnaces with an input capacity of100,000 Btuh or less—from any non-
mechanical air supply (windows or doorswhich can be opened) or combustion-air
opening
11
For furnaces with an input capacity greaterthan 100,000 Btuh or less—from any non-
mechanical air supply (windows or doorswhich can be opened) or combustion-air
opening
13
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 355MAV furnaces, refer to Multiventing and Vent Terminations section for proper vent configurations.
2. When locating combustion-air and vent terminations, consideration must begiven 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.
4. Vent termination must be at least 3 feet above any forced draft inlets within 10 feet horizontal. Vent termination must be at least 3 feet horizontal from other
direct vent appliances intake unless otherwise specified by manufacturer.
Fig. 35—Combustion-Air and Vent Pipe Diameter Transition Location and Elbow Configuration
A93034
FURNACE
PIPE DIAMETER
TRANSITION IN
VERTICAL SECTION
NOT IN
HORIZONTAL
SECTION
—31—