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Technical Training Department
Ashland City, Tennessee
SBN TANK TYPE COMMERCIAL GAS WATER HEATER
SERVICE HANDBOOK
©2003
Often, it is more practical to install vertical make-up ducts to the outdoors.
Make-Up Air - Vertical Ducts
Again, two openings are required: one within 12 inches of the top of the enclosure
and one within twelve inches of the bottom of the enclosure. Each opening must
have a free area of not less than 1 square inch per 4,000 BTUH of the total input of
all appliances within the enclosure.
When the heater is installed in an interior room with no roof access for vertical ducts,
horizontal make-up air ducts should be installed. When using horizontal ducts, two
openings are required - one within 12 inches of the top of the enclosure and one within
12 inches of the bottom of the enclosure. Each opening must have a free area of not
less than 1 square inch per 2,000 BTUH of the total input of all appliances within the
enclosure.
Make-Up Air - Horizontal Ducts
