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
FIGURE 13.
3.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 cm2/kW) of total input rating of all equipment in the enclosure, see Figure 14.
4.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” (76.2 mm), see Figure 14.
5.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
FIGURE 14.
6.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.
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