All Air From Outdoors - American Water Heater Flame Guard Safety System Installation Instructions And User Manual

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
Table 4 to calculate the minimum free area for each
opening. Figures 6, 7, and 8 are typical examples of
each method.
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.
Table 4
Minimum Free Area of Permanent Openings for Ventilation and
Combustion Air Supply - All Air from Outdoors Only.
Based on the total BTUH input rating for all gas utilizing equipment
within the confined space.
Minimum Free Area
Opening
Per Opening
Source
Direct to 1 Square inch per 4000
outdoors
Vertical ducts 1 Square inch per 4000
Horizontal ducts 1 Square inch per 2000
Example: A water heater with an input rate 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. Inches.
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.
Reference
Drawing
(sq. in.)
Figure 6
BTUH
Figure 7
BTUH
Figure 8
BTUH
Confined
Space
Alternate
Air Inlet
1 sq. inch per
4000 BTUH
Figure 6
All Air from Outdoors; Inlet Air from Ventilated
Crawl Space/Outlet Air to Ventilated Attic
Confined
Space
Figure 7
All Air from Outdoors
Through Ventilated Attic
Confined
Space
Figure 8
All Air from Outdoors
Using Horizontal Ducts
Gable 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
Inlet air duct
1 sq. inch per
4000 BTUH
12" max.
1 sq. inch
per
2000 BTUH
Outlet
Outdoor
Air Ducts
Inlet
1 sq. Inch
per
2000 BTUH
9