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Air Requirements
Important: Air for combustion and ventilation must not
come from a corrosive atmosphere. Any failure due to cor-
rosive elements in the atmosphere is excluded from war-
ranty coverage.
Installations in or for certain places including, but not limited
to, those listed below will require outdoor air for combustion
due to chemical exposure:
Beauty shops
Photo processing labs
Buildings with indoor pools
Water heaters installed in laundry, hobby or craft rooms
Water heaters installed near chemical storage areas
In such circumstances, outdoor combustion air may reduce,
but will not eliminate, the presence of corrosive chemicals in
the air. Combustion air must be free of acid-forming chemi-
cals such as sulfur, fluorine and chlorine. These elements
are found in aerosol sprays, detergents, bleaches, cleaning
solvents, air fresheners, paint and varnish removers, refrig-
erants and many other commercial and household prod-
ucts. When burned, vapors from these products form highly
corrosive acid compounds. These products should not be
stored or used near the water heater or air inlet.
The area in which the heater is located is classified as either
“an unconfined sp
ace
” or “a confined sp
ace
”.
An unconfined sp
ace
is defined as a space having a vol-
ume not less than 50 cubic feet per 1000 BTU/hour (4.8
cubic metres per kilowatt) of combined input rating of all
appliances using the space. Adjacent open rooms may be
included as part of the unconfined space, provided there are
no closeable doors between these rooms. An example of
this is an open basement.
A confined sp
ace is one smaller than described above.
For buildings using tight construction (newer and renovated
structures), the air supply shall be introduced from the out-
doors, regardless of whether the space is confined or
unconfined.
Confined Space Air Requirements for
Canadian Installations
Refer to Figure 5 (a), or (b), and Table 1 for proper sizing
and location of combustion air ducts and openings. CHECK
LOCAL CODES.
(a). Two permanent openings shall be provided connecting
the confined space (e.g., closet, small room) with the
unconfined space. Each opening shall have a free area
of one square inch per 1,000 BTU/hour input (22
cm²/kW) of all appliances in the confined space. The top
opening shall be located as close to the ceiling as prac-
tical but never lower than the top of the heater. (see
Figure 5 (a)). The bottom opening shall be located nei-
ther more than 450mm (18 in.), nor less than 150mm (6
in.), above floor level.
(b). When using a single air supply, the duct shall terminate
within 300mm (12 in.) above and within 600mm (24 in.)
horizontally of the burner level of the appliance having
the largest input. For example: GSW’s water heaters’
burners are 150mm (6 in.) from the floor, plus 300mm
(12 in.) equals 450mm (18 in.) as shown in Figure 5 (b).
All exterior vent openings are to be at least 300mm (12
in.) above the ground and clear of snow levels.
– 9 –
CONFINED
SPACE
PERMANENT
OPENINGS
EQUIPMENT LOCATED IN CONFINED SPACES;
ALL AIR FROM INSIDE THE BUILDING.
(a)
UNCONFINED
SPACE
BASEMENT INSTALLATION, EQUIPMENT LOCATED
IN CONFINED SPACES; ALL AIR FROM OUTDOORS
(b)
CONFINED
SPACE
GRADE
COMBINATION
COMBUSTION/
VENTILATION
AIR DUCT
300mm
(12 in.)
(MIN)
450mm (18 in.)
600mm (24 in.)
Figure 5 Combustion Air Supply Openings And Ducts
(Can.)
BTU / h (kW / hr)
cm
2
in.
2
mm in. mm in.
25,000 8 45 7 76 3 100 4
50,000 15 45 7 76 3 100 4
75,000 23 70 11 100 4 125 5
100,000 30 90 14 100 4 125 5
125,000 37 120 18 125 5 150 6
150,000 45 140 22 125 5 150 6
Acceptable Round
Duct Size Diameter
Combined Input
of All Appliances
in Confined
Space*
Required
Free Area
A**
B***
Table 1 Air Supply Sizing (Can.)
* All appliances refers to, and includes, those appliances
using the same air source (e.g. water heater, furnace,
boiler, clothes dryer etc.).
** Maximum allowable length of ductwork listed in column
A is 6.1 equivalent metres (20 ft.).
*** Maximum allowable length of ductwork listed in column
B is 15.2 equivalent metres (50 ft.)