Confined Space Air Requirements for

Air Requirements	b). When using a single air supply, the duct shall terminate
Important: Air for combustion and ventilation must not	within 300mm (12 in.) above and within 600mm (24 in.)
come from a corrosive atmosphere. Any failure due to cor-	horizontally of the burner level of the appliance having
rosive elements in the atmosphere is excluded from war-	the largest input. For example: GSW’s water heaters’
ranty coverage.	burners are 150mm (6 in.) from the floor, plus 300mm
Installations in or for certain places including, but not limited	(12 in.) equals 450mm (18 in.) as shown in Figure 4 (b).
to, those listed below will require outdoor air for combustion	All exterior vent openings are to be at least 300mm (12
due to chemical exposure:	in.) above the ground and clear of snow levels.

Beauty shops
Photo processing labs				(a)
Buildings with indoor pools				(a)
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,																								PERMANENT
but will not eliminate the presence of corrosive chemicals in

																								OPENINGS
the air. Combustion air must be free of acid-forming chemi-																								OPENINGS
the air. Combustion air must be free of acid-forming chemi-
cals such as sulfur, fluorine and chlorine. These elements				CONFINED																		UNCONFINED
cals such as sulfur, fluorine and chlorine. These elements				CONFINED
are found in aerosol sprays, detergents, bleaches, cleaning					SPACE
are found in aerosol sprays, detergents, bleaches, cleaning																						SPACE
solvents, air fresheners, paint and varnish removers, refrig-
erants and many other commercial and household prod-								EQUIPMENT LOCATED IN CONFINED SPACES;
ucts. When burned, vapours from these products form high-								EQUIPMENT LOCATED IN CONFINED SPACES;
ucts. When burned, vapours from these products form high-										ALL AIR FROM INSIDE THE BUILDING.
ly corrosive acid compounds. These products should not be										ALL AIR FROM INSIDE THE BUILDING.


stored or used near the water heater or air inlet.				(b) (12 in.)																CONFINED
The area in which the heater is located is classified as either						300mm															SPACE
						(MIN)															SPACE

“an unconfined space” or “a confined space.”
“an unconfined space” or “a confined space.”
An unconfined space is defined as a space having a vol-
An unconfined space 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					GRADE
appliances using the space. Adjacent open rooms may be				COMBINATION
appliances using the space. Adjacent open rooms may be				COMBINATION
included as part of the unconfined space, provided there				COMBUSTION/
included as part of the unconfined space, provided there				COMBUSTION/
are no closeable doors between these rooms. An exam-					VENTILATION
					VENTILATION
					AIR DUCT
ple of this is an open basement.																		600mm (24 in.)
A confined space is one smaller than described above.									450mm (18 in.)


For buildings using tight construction (newer and renovated							BASEMENT INSTALLATION, EQUIPMENT LOCATED
structures), the air supply shall be introduced from the out-							BASEMENT INSTALLATION, EQUIPMENT LOCATED
							IN CONFINED SPACES; ALL AIR FROM OUTDOORS
doors, regardless of whether the space is confined or
doors, regardless of whether the space is confined or		Figure 4 Combustion Air Supply Openings And Ducts
unconfined.		Figure 4 Combustion Air Supply Openings And Ducts
unconfined.									(Can.)
									(Can.)
Confined Space Air Requirements for

	Combined Input of																	Acceptable Round
Canadian Installations	Combined Input of												Required					Duct Size Diameter
Refer to Figure 4 (a), or (b), and Table 1 for proper sizing			All Appliances in								Free Area
			All Appliances in																A**					B***
			Confined Space*																A**					B***
and location of combustion air ducts and openings. CHECK
LOCAL CODES.	BTU / h							(kW / hr)				cm2			in.2		mm			in.			mm		in.
a). Two permanent openings shall be provided connecting	25,000							8			45			7		76				3		100			4
the confined space (e.g., closet, small room) with the	25,000							8			45			7		76				3		100			4
the confined space (e.g., closet, small room) with the	50,000							15			45			7		76				3		100			4
unconfined space. Each opening shall have a free area	50,000							15			45			7		76				3		100			4
unconfined space. Each opening shall have a free area	75,000							23			70			11		100				4		125			5
of one square inch per 1,000 BTU/hour input (22	75,000							23			70			11		100				4		125			5
of one square inch per 1,000 BTU/hour input (22	100,000							30			90			14		100				4		125			5
cm²/kW) of all appliances in the confined space. The top	100,000							30			90			14		100				4		125			5
cm²/kW) of all appliances in the confined space. The top	125,000							37			120			18		125				5		150			6
opening shall be located as close to the ceiling as prac-	125,000							37			120			18		125				5		150			6
opening shall be located as close to the ceiling as prac-	150,000							45			140			22		125				5		150			6
tical but never lower than the top of the heater. (see	150,000							45			140			22		125				5		150			6
tical but never lower than the top of the heater. (see
Figure 4 (a)). The bottom opening shall be located nei-
Figure 4 (a)). The bottom opening shall be located nei-		* All appliances refers to, and includes, those appliances
ther more than 450mm (18 in.), nor less than 150mm (6					using the same air source (e.g. water heater, furnace,
in.), above floor level.					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.).
	Table 1 Air Supply Sizing (Can.)
– 9	–

Air Requirements

“an unconfined space” or “a confined space.”

are no closeable doors between these rooms. An exam-

Figure 4 Combustion Air Supply Openings And Ducts

Confined Space Air Requirements for

Canadian Installations

LOCAL CODES.

Figure 4 (a)). The bottom opening shall be located nei-

* All appliances refers to, and includes, those appliances

ther more than 450mm (18 in.), nor less than 150mm (6

using the same air source (e.g. water heater, furnace,

in.), above floor level.

boiler, clothes dryer etc.).

** Maximum allowable length of ductwork listed in column

A is 6.1 equivalent metres (20 ft.).

B is 15.2 equivalent metres (50 ft.).

Table 1 Air Supply Sizing (Can.)