6
total input rating of all appliances in the enclosed
space.
(Figure #5)
If horizontal ducts are used, each opening shall have
C.
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.
space shall be provided with two permanent openings,
one commencing within 12 inches from the top and
one commencing 12 inches from the bottom of the
enclosure. The openings shall communicate directly,
or by ducts, with the outdoors or spaces (crawl or attic)
that freely communicate with the outdoors. One of the
following methods must be used to provide adequate
air for ventilation and combustion.
When directly communicating with the outdoors, each
A.
opening shall have a minimum free area of 1 square
inch per 4,000 BTU per hour of total input rating of all
equipment in the enclosure.
(Figure #4)
When communicating with the outdoors by means of
B.
vertical ducts, each opening shall have a minimum
free area 1 square inch per 4,000 BTU per hour of
VENTILATION AND COMBUSTION AIR
Figure #4
Figure #5
Figure #6
