8
If horizontal ducts are used, each opening and duct
III.
shall have a minimum free area 1 square inch per
2,000 BTU per hour of total input rating of all appli
-
ances in the enclosed space. See
figure #4
.
BOILER
-- SLAB --
INLET AIR DUCT
12"
INLET AIR DUCT
12"
Figure #4
One permanent opening, commencing within 12 inches
B.
of the top of the enclosure, shall be permitted where the
equipment has clearances of at least 1 inch from the
sides, 1 inch from the back, and 6 inches from the front
of the boiler. The opening shall directly communicate
with the outdoors or shall communicate through a verti
-
cal or horizontal duct to the outdoors or spaces (crawl
or attic) that freely communicate with the outdoors. The
openings must have a minimum free area of 1 square
inch per 3000 Btu per hour of the total input rating of all
equipment located in the enclosure. The free area must
be no less than the sum of the areas of all vent connec
-
tors in the confined space.
VENTILATION & COMBUSTION AIR
In calculating free area using louvers, grilles or screens
6.
for the above, consideration shall be given to their block-
ing 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
grilles will have 60-75% free area. Louvers and grilles
should be fixed in the open position or interlocked with the
boiler so they are opened automatically during the boiler
operation.