John Wood Atmospheric Gas (Standard) - Manual (Page 12)

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However, it must never be lower than the relief opening of
the draft hood. See Figure 4.
AS CLOSE TO CEILING AS POSSIBLE AND
PERMANENT
OPENINGS TO
ADDITIONAL
ROOMS WITHIN
THE BUILDING
CLOSET
OR
OTHER
CONFINED
SPACE
NO LESS THAN 6 INCHES (15.2 cm) AND
NO MORE THAN 18 INCHES (45.7 cm)
ABOVE FLOOR LEVEL.
ABOVE DRAFT HOOD.
FIGURE 4.
Each of the two openings shall have a minimum free area
of 1 square inch per 1,000 BTU/HR (2225mm² per kW) of
the total input rating of all gas utilization equipment in the
confined area, but not less than 100 square inches (645.16
cm 2 ). See Figure 5.
CONFINED
SPACE
PERMANENT
OPENINGS
1 SQUARE
INCH/1000
BTUH
(MINIMUM
100 SQ. IN.)
See text for
metric values.
FIGURE 5.
For specific ventilation and combustion air requirements,
consult the Natural Gas and Propane Installation Code
(CAN/CSA B149.1-current edition) and the local codes of
your area.
All Air from Outdoors
Outdoor fresh air can be provided to a confined area either
directly or by the use of ducts. The fresh air can be taken
from the outdoors or from crawl or attic spaces that freely
communicate with the outdoors. Attic or crawl spaces
cannot be closed and must be properly ventilated to the
outside.
Ductwork must be of the same cross-sectional area as
the free area of the opening to which they connect. The
minimum dimension of rectangular air ducts cannot be less
than three inches (7.62 cm). In addition, the duct must
terminate within 1 foot (30.5 cm) above, and within 2 feet
(61 cm) horizontally from, the burner level of the appliance
having the largest input. See Figure 6.
BASEMENT INSTALLATION, EQUIPMENT LOCATED
IN CONFINED SPACES; ALL AIR FROM OUTDOORS
CONFINED
SPACE
GRADE
COMBINATION
COMBUSTION/
VENTILATION
AIR DUCT
12 in.
(30.5 cm)
MINIMUM
ABOVE GRADE
& SNOW LEVELS
WITHIN 12 in. (30.5 cm)
ABOVE BURNER LEVEL WITHIN 24 in. (61 cm)
FIGURE 6.
An opening may be used in lieu of a duct to provide the
outside air supply. It, too, must be located within 1 foot
(30.5 cm) above, and within 2 feet (61 cm) horizontally from,
the burner level of the appliance having the largest input.
However, it must be located at least 12 inches (30.5 cm)
above the outside grade level and be clear of snow levels.
In addition, it must be equipped with a means to prevent the
direct entry of rain and wind without reducing the required
free area of the opening.
The size of openings is determined by the method in which the
air is to be provided. For specific ventilation and combustion air
requirements, consult the Natural Gas and Propane Installation
Code (CAN/CSA B149.1-current edition) and the local codes of
your area.
Louvers and Grilles
In calculating free area for ventilation and combustion
air supply openings, consideration must be given to the
blocking effect of protection louvers, grilles, and screens.
These devices can reduce airflow, which in turn may
require larger openings to achieve the required minimum
free area. Screens must not be smaller than 1/4” (6.35
mm) mesh. If the free area through a particular design of
louver or grille is known, it should be used in calculating
the specified free area of the opening. If the design and
free area are not known, it can be assumed that most
wood louvers will allow 20 - 25% of free area while metal
louvers and grilles will allow 60 - 75% of free area.
Louvers and grilles must be interconnected with the
equipment so that they are opened automatically during
equipment operation. Also, keep louvers and grilles clean
and free of debris or other obstructions. Do not use
manually adjustable louvers.
Vent Pipe System
This water heater uses a non-direct, single-pipe vent
system to remove exhaust gases created by the burning of
fossil fuels. Air for combustion is taken from the immediate
water heater location or is ducted in from the outside (see
“Combustion Air Supply and Ventilation.”)
This water heater must be properly vented for the removal
of exhaust gases to the outside atmosphere. Correct
installation of the vent pipe system is mandatory for the
proper and efficient operation of this water heater and is
an important factor in the life of the unit.
The vent pipe must be installed according to CAN/