Lochinvar COMMERCIAL GAS WATER HEATERS Instruction Manual page 9

combined space shall be considered in making this determination. Each
opening shall have a minimum free area of one square inch per 1,000
2
Btu per hour (22 cm /kW) of the total input rating of all gas utilization
equipment in the confi ned space, but not less than 100 square
inches (645 cm 2 ). One opening shall commence within 12 inches
(30 cm) of the top and one commencing within 12 inches (30 cm)
of the bottom of the enclosures.
FIGURE 5.
B. ALL AIR FROM OUTDOORS: (See Figures 6, 7 and 8)
The confi ned space shall 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 shall communicate directly, or by ducts, with the outdoors
or spaces (crawl or attic) that freely communicate with the outdoors.
• When directly communicating with the outdoors, each opening
shall 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 6.
FIGURE 6.
• When communicating with the outdoors through vertical ducts,
each opening shall have a minimum free area of 1 square inch
per 4,000 Btu per hour (5.5 cm
equipment in the enclosure, see Figure 8.
• When communicating with the outdoors through horizontal ducts,
each opening shall have a minimum free area of 1 square inch
per 2,000 Btu per hour (11 cm
equipment in the enclosure, see Figure 9.
• 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 shall 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 7.
2
/kW) of total input rating of all
2
/kW)) of total input rating of all
• When ducts are used, they shall 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 shall not
be less than 3 inches (76.2 mm), see Figure 9.
• Louvers and Grilles: In calculating free area, consideration shall be given
to the blocking effect of louvers, grilles or screens protecting openings.
Screens used shall 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
specifi ed. 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 shall
be fi xed in the open position or interlocked with the equipment so that
they are opened automatically during equipment operation.
• Special Conditions Created by Mechanical Exhausting or Fireplaces:
operation of exhaust fans, ventilation systems, clothes dryers or
fi replaces may create conditions requiring special attention to avoid
unsatisfactory operation of installed gas utilization equipment.
9
FIGURE 7.
FIGURE 8.
FIGURE 9.