State Industries GP650HTPDT - Manual (Page 12)

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a free area of one square inch per 1000 Btu/hr (22 cm 2 /kW) of the
total input of all appliances in the enclosure, but not less than 100
square inches (645 cm 2 ).
If the confined space is within a building of tight construction, air for
combustion and ventilation must be obtained from outdoors. When
directly communicating with the outdoors or communicating through
vertical ducts, two permanent openings, located in the above manner,
should be provided. Each opening should have a free area of not less
than one square inch per 4000 Btu/hr (5.5 cm 2 /kW) of total input of all
appliances in the enclosure. If horizontal ducts are used, each opening
should have a free area of not less than one square inch per 2000 Btu/
hr (11cm 2 /kW) of the total input of all appliances in the enclosure.
a. all aIr froM InsIde BuIldInGs: (See Figure 5 and 6)
The confined space should be provided with two permanent openings
communicating directly with an additional room(s) of sufficient volume
so that the combined volume of all spaces meets the criteria for an
unconfined space. The total input of all gas utilization equipment installed
in the combined space should be considered in making this determination.
Each opening should have a minimum free area of one square inch
per 1,000 Btu per hour (22 cm 2 /kW) of the total input rating of all gas
utilization equipment in the confined space, but not less than 100 square
inches (645 cm 2 ). One opening should commence within 12 inches
(30 cm) of the top and one commencing within 12 inches (30 cm) of the
bottom of the enclosures.
FIGURE 6.
B. all aIr froM outdoors: (See Figures 7, 8 and 9)
The confined space should be provided with two permanent openings,
one commencing within 12 inches (30 cm) of top and one commencing
within 12 inches (30 cm) from the bottom of the enclosure. The
openings should communicate directly, or by ducts, with the outdoors
or spaces (crawl or attic) that freely communicate with the outdoors.
1. When directly communicating with the outdoors, each opening should have
a minimum free area of 1 square inch per 4,000 Btu per hour (5.5 cm 2 /kW) of
total input rating of all equipment in the enclosure, see Figure 7.
FIGURE 7.
2. When communicating with the outdoors through vertical ducts, each
opening should have a minimum free area of 1 square inch per 4,000
Btu per hour (5.5 cm2/kW) of total input rating of all equipment in the
enclosure, see Figure 8.
3. When communicating with the outdoors through horizontal ducts, each
opening should have a minimum free area of 1 square inch per 2,000
Btu per hour (11 cm2/kW)) of total input rating of all equipment in the
enclosure, see Figure 9A.
FIGURE 8.
4. When ducts are used, they should be of the same cross-sectional area
as the free area of the openings to which they connect. The minimum
short side dimension of rectangular air ducts should not be less than
3 inches (7.6 cm), see Figure 9A.
FIGURE 9A.
5. Alternatively a single permanent opening may be used when
communicating directly with the outdoors, or with spaces that freely
communicate with the outdoors. The opening should have a minimum
free area of 1 square inch per 3,000 BTU per hour (8.3 cm2/kW) of total
input rating of all equipment in enclosure. See Figure 9B.
FIGURE 9B.
6. Louvers and Grilles: In calculating free area, consideration should
be given to the blocking effect of louvers, grilles or screens protecting
openings. Screens used should not be smaller than 1/4 inch (6.4 mm)
mesh. If the free area through a design of louver or grille 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 be 20-25 percent free area and metal
louvers and grilles will have 60-75 percent free area. Louvers and grilles
should be fixed in the open position or interlocked with the equipment
so that they are opened automatically during equipment operation.
7. Special Conditions Created by Mechanical Exhausting or Fireplaces:
operation of exhaust fans, ventilation systems, clothes dryers or
fireplaces may create conditions requiring special attention to avoid
unsatisfactory operation of installed gas utilization equipment.