John Wood Envirosense Power Vent - Manual (Page 11)

11
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 the 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 cm 2 /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 cm 2 /kW)) of total input rating of all
equipment in the enclosure, see Figure 9.
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 9.
fIGure 9.
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 cm 2 /kW) of total input rating of all equipment in enclosure.
See Figure 9A.
fIGure 9a.
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.