A.O. Smith GCV Series Service Handbook page 14

All Air from Inside the Building: When additional air
is to be provided to the confi ned area from additional
room(s) within the building, the total volume of the
room(s) must be of suffi cient size to properly provide
the necessary amount of fresh air to the water heater
and other gas utilization equipment in the area. Each
of the two openings shall have a minimum free area of
1 square inch per 1,000 BTUH of the total input rating
of all gas utilization equipment in the confi ned area, but
not less than 100 square inches for each opening.
Figure 8
All Air from Outdoors: Outdoor fresh air can be
provided to a confined area either directly or by the use
of vertical and horizontal 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.
The size of each of the two openings is determined by
the method in which the air is to be provided. Refer to
the table below to calculate the minimum free area for
each opening.
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" 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 locked open or
interconnected with the equipment so that they are
opened automatically during equipment operation.
Keep louvers and grilles clean and free of debris or
other obstructions.
BASIC INSTALLATION & OPERATION
CONFINED
SPACE
PERMANENT
OPENINGS
1 SQUARE
INCH/1000
BTUH
(MINIMUM
100 SQ. IN.
FOR EACH
OPENING)
Minimum Free Area of Permanent Openings for
Ventilation and Combustion Air Supply - All Air from
Outdoors Only.
Based on total BTUH input rating for all utilizing
equipment within the confi ned space.
Minimum Free Area
Opening Source Per Opening (sq. in.)
*Direct to outdoors 1 sq. in, per 4000 BTUH
Vertical Ducts 1 sq. in, per 4000 BTUH
Horizontal Ducts 1 sq. in, per 2000 BTUH
Single Opening 1 sq. in, per 3000 BTUH
Example: A water heater with an input rating of 50,000 BTUH
using horizontal ducts would require each opening to have a
minimum free area of 25 square inches.
Minimum free area = 50,000 BTUH x 1 sq. in. / 2000 BTUH = 25
sq. in.
These openings connect directly with the outdoors
*
through a ventilated attic, a ventilated crawl space, or
through an outside wall.
Consult the local codes of your area for specific
ventilation and combustion air requirements
CONFINED
SPACE
ALTERNATE
AIR INLET
1 SQ. INCH PER
4000 BTUH
100 SQ. INCH MINIMUM (EACH)
ALL AIR FROM OUTDOORS: INLET AIR FROM VENTILATED
CRAWL SPACE/OUTLET AIR TO VENTILATED ATTIC
Figure 9
CONFINED
SPACE
ALL AIR FROM OUTDOORS THROUGH VENTILATED ATTIC
Figure 10
14
Reference
Drawing
Figure 9
Figure 10
Figure 11
Figure 12
ABLE VENT
TO OUTDOORS
INSTALL ABOVE
INSULATION
OUTLET
AIR TO
ATTIC 1 SQ.
INCH PER
4000 BTUH
INLET AIR FROM
THE CRAWL SPACE
OPEN
FOUNDATION
VENT
GABLE VENT
TO OUTDOORS
INSTALL ABOVE
INSULATION
OUTLET AIR TO
ATTIC 1 SQ. INCH
PER 4000 BTUH -
100 SQ. INCH MIN.
(EACH)
INLET AIR DUCT
1 SQ. INCH PER
4000 BTUH - 100
SQ. INCH MIN.
(EACH)
12" MAXIMUM