6
If horizontal ducts are used, each opening shall
C.
have a minimum free area 1 square inch per 2,000
BTU per hour total input rating of all appliances in
the enclosed space. (Figure #6)
When ducts are used, they shall be of the same
D.
cross sectional area as the free area of the area of
the openings to which they connect. The minimum
dimension of rectangular air ducts shall not be less
than 3 inches.
In calculating free area using louvers, grills or screens
6.
for the above, consideration shall be given to their
blocking effect. Screens used shall not be smaller than
1/4 inch mesh. If the free area through a design of
louver or grill is known, it should be used in calculating
the size opening required to provide the free area
specified. If the design and free area is not known, it
may be assumed that wood louvers will have 20-25%
free area and metal louvers and grills will have 60-75%
free area. Louvers and grills shall be fixed in the open
position or interlocked with the boiler so that they are
opened automatically during boiler operation.
Figure #2
Figure #3
Figure #4
VENTILATION AND COMBUSTION AIR
