A.O. Smith VB/VW- 1000 - Manual (Page 13)

13
AIR FROM OTHER INDOOR SPACES
FIGURE 9E.
The confined space should be provided with two permanent
openings, one commencing within 12 inches (300 mm) of the top
and one commencing within 12 inches (300 mm) of the bottom of
the enclosure. See Figure 9E.
Each opening should communicate directly with an additional
room(s) of sufficient volume so that the combined volume of all
spaces meets the criteria for an Unconfined Space.
Each opening should have a minimum free area of 1 square inch
per 1,000 Btu/hr (1100 mm 2 per kW) of the aggregate input rating
of all appliances installed in the enclosure. Each opening should
not be less than 100 square inches (645 cm 2 ).