Use and Care Manual

LP-436 Rev. 5.2.18
8
C. Combustion and Ventilation Air Supply
In order for the water heater to operate properly, it must be supplied
with an uninterrupted ow of clean combustion and ventilation air.
The area around the water heater must always be kept clear so that the
ow of combustion and ventilation air is not blocked. An inadequate
supply of air to the water heater will produce a bright yellow burner
ame, causing sooting in the combustion chamber, on the burners,
and in the ue tubes. This can result in damage to the water heater and
serious bodily injury if not corrected.
Combustion and ventilation air requirements are determined by
the water heater location. Water heaters are installed in either open
(unconned) spaces or smaller (conned) spaces, such as closets or
small rooms.
1. Requirements for Unconned Spaces
An unconned space is an area with at least 50 cubic feet for each 1,000
BTU/H of the total input rating for all gas-red appliances installed in
that space. Water heaters installed in unconned spaces do not usually
require outdoor air to function properly. However, in buildings with
tight construction (heavy insulation, vapor 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 for conned spaces.
2. Requirements for Conned Spaces
In the US (refer to ANSI Z223.1/NFPA 54)
a. All Air From Inside the Building
The conned space shall be provided with two permanent openings
communicating directly with one or more rooms of sucient volume,
so that the combined volume of all spaces meets the criteria for an
unconned 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 BTU/H (22cm
2
/kW) of the total input rating of all gas
appliances in the conned space, but not less than one hundred (100)
square inches (645.16 cm
2
). One opening shall commence within six
(6) inches (15.2 cm) of the top and one within six (6) inches (15.2 cm) of
the bottom of the enclosure.
Figure 3 - Conned Space - All Air from Inside Building
b. All Air From Outdoors
The conned space shall be provided with two permanent openings,
one commencing within six (6) inches (15.2 cm) of the top and one
commencing within six (6) inches (15.2 cm) from the bottom of the
enclosure. The openings shall communicate directly or by ducts with
Figure 4 - Conned Space - Communicating Directly with Outdoors
2) When communicating with the outdoors through vertical ducts,
each opening shall have a minimum free area of one (1) square inch
per 4,000 BTU/H (5.5 cm
2
/kW) of the total input rating of all gas
appliances in the enclosure. See Figure 5.
Figure 5 - Conned Space - Communicating Outdoors through Vertical
Ducts
When drawing combustion air from the outside into the
mechanical room, care must be taken to provide adequate freeze
protection.
Failure to provide an adequate supply of fresh combustion air can
cause poisonous ue gases to enter the living space, resulting in
severe personal injury or death.
A conned space is an area where the volume is less than 50 cubic feet
for each 1,000 BTU/H of the total input rating for all gas appliances
installed in that space. Water heaters installed in conned spaces
require additional combustion and ventilation air. This can be provided
in two ways:
the outdoors or spaces (crawl or attic) that freely communicate with
the outdoors.
1) When communicating directly with the outdoors, each opening
shall have a minimum free area of one (1) square inch per 4,000
BTU/H (5.5 cm
2
/kW) of the total input rating of all gas appliances in
the enclosure. See Figure 4.