Combustion and Ventilation Air Supply
In order for the water heater to operate properly, it
must be supplied with an uninterrupted flow of clean
combustion and ventilation air. The area around the
water heater must always be kept clear and the
combustion air intake holes at the bottom of the
water heater must never be blocked. An inadequate
supply of air to the water heater will produce a
bright yellow burner flame causing sooting in the
combustion chamber, on the burner, and in the flue
tube. This can result in damage to the water heater
and serious bodily injury, if not corrected.
Combustion and ventilation air requirements are
determined by where the water heater will be located.
Water heaters are installed in either open (unconfined)
spaces or smaller (confined) spaces, such as closets
or small rooms.
Requirements for Unconfined Spaces
An unconfined space is an area with at least fifty
(50) cubic feet for each 1,000 Btuh (4.8 m/kW) of
the total input rating for all gas appliances installed
in that space. Water heaters installed in unconfined
spaces do not usually require outdoor air to function
properly. However, in buildings with tight construction
(heavy insulation, vapour barriers, weather stripping,
etc.), and particularly in modern buildings, additional
fresh air may need to be provided. For instructions on
obtaining additional air supply, see the requirements
below for confined spaces.
Requirements for Confined Spaces
A confined space is an area where the volume is
less then fifty (50) cubic feet for each 1,000 Btuh
(4.8 m³/kW) of the total input rating for all gas
appliances installed in that space. Water heaters
installed in confined spaces require additional
combustion and ventilation air. This can be provided
in two ways:
In Canada refer to CSA B149.1 and local codes for
detailed information.
1) The enclosure in which the water heater is installed
shall be provided with two (2) permanent openings
of one (1) square inch per 1,000 Btuh (22.0 cm²/
kW) of the total input of all appliances and shall
communicate directly with one or more rooms of
sufficient volume, so that the combined volume of all
spaces meets the criteria for an unconfined space
for all the appliances installed in that enclosure.
One opening shall be located not more than
eighteen (18) inches (45.7 cm) or less than six (6)
inches (15.2 cm) above the floor level. The second
shall be located as near the ceiling as practical, but
in no case lower than the draft hood.
2) All Air from Outdoors (see Figure 3):
An air supply shall be provided with one opening
that communicates directly with the outdoors by
means of a duct. This duct shall be sized according
to CSA B149.1 and terminate within one (1) foot
(30.5 cm) above, and within two (2) feet (61 cm)
horizontally from the burner level of the appliance
having the largest input.
In U.S.A. (refer to ANSI Z223.1/NFPA 54 and local
codes for detailed information.
1) All Air From Inside the Building (see Figure 2)
:
The confined space shall be provided with two
(2) permanent openings communicating directly with
one or more rooms of sufficient volume, so that the
combined volume of all spaces meets the criteria
for an unconfined space. The total input rating of
all gas appliances installed in the combined space
shall be considered in making this determination.
Each opening shall have a minimum free area of
one (1) square inch per 1,000 Btuh (22.0 cm/kW)
of the total input rating of all gas appliances in the
confined space, but not less than one hundred
5
INSTALLATION INSTRUCTIONS
Confined Space
Permanent
Opening
--------------
1 square inch /
1,000 Btuh
(min.: 100 sq. in)
Outlet air to attic
1 sq. in / 4,000 Btuh
Attic air inlet
Install above
insulation
Confined Space
Inlet air from the
crawl space
1 sq. in / 4,000 Btuh
Open foundation vent
Install above
insulation
Attic air inlet
Outlet air to attic
1 sq. in / 4,000 Btuh
Confined Space
Inlet air duct
1 sq. in / 4,000 Btuh
12'' max.
Inlet
Outlet
Outdoor air duct
1 sq. in. / 2,000 Btuh
1 sq. in. / 2,000 Btuh
Confined Space
Alternate
air inlet
Entrée d'air
Alternative
1 po
2
/ 2 000 BTUH
1 po
2
/ 2 000 BTUH
Conduit d'air extérieur
Sortie
Entrée
12'' max.
Conduit d'entrée d'air
1 po
2
/ 4 000 BTUH
Évent de fondation
1 po
2
/ 4 000 BTUH
Entrée d'air du
sous-sol
Espace Restreint
Installez au-dessus
de l'isolation
Entrée d'air
du grenier
Sortie d'air
au grenier
1 po
2
/ 4 000 BTUH
Ouverture
Permanente
--------------
1 pouce carré /
1 000 BTUH
(min. : 100 po
2
)
Espace Restreint
Entrée d'air
du grenier
Installez au-dessus
de l'isolation
Espace Restreint
Sortie d'air
au grenier
1 po
2
/ 4 000 BTUH
Espace Restreint
Gas vent to
outdoors
Évacuation de gaz
vers l'extérieur
Gas vent to
outdoors
Évacuation de gaz
vers l'extérieur
Gas vent to
outdoors
Évacuation de gaz
vers l'extérieur
Gas vent to
outdoors
Évacuation de gaz
vers l'extérieur
Figure 2
Espace confiné
Conduit
d’entrée d’air
18'' (45 cm)
24'’ (60 cm)
18'' (45 cm)
24'’ (60 cm)
Confined Space
Inlet air duct
Figure 3
