Fixtures & Water HeatersQuestion 71 of 120
A 120,000 Btu/h gas water heater draws all of its combustion air directly from outdoors through two vertical ducts. Using the 1 square inch per 4,000 Btu/h rule for vertical ducts, what is the required free area of each opening?
a.15 square inches
b.30 square inches
c.60 square inches
d.12 square inches
Explanation
Dividing 120,000 by 4,000 gives 30 square inches, and that is the required free area for each of the two openings, one near the top and one near the bottom of the enclosure. 60 square inches is the combined area of both openings, not the size of each. 15 square inches halves the correct figure, and 12 square inches corresponds to no recognized ratio.
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