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Atmospheric, Single, and Multiple Heaters
All SBD water heaters are classified by ANSI as category I (non-condensing, negative
pressure venting) appliances. They are approved for type B vent.
For larger applications, SBD water heaters can be common vented together either in a
tapered manifold or constant size manifold. (Follow National Fuel Gas Code
requirements for sizing and installation.)
Combined Vents
When vents are combined, the area of the combined vent should be equal to area of the
largest single vent, plus 50% of area of all others joining.
Nine Rules for Good Vents
1. The vent pipe should ALWAYS be the same size as
the outlet of the draft diverter or factory supplied vent
reducer.
Model SBD 120 are supplied with a 6" to 5"
reducer.
Models SBD 250, 251 and 275 are
supplied with a 8" to 6" reducer.
Technical Training Department
Ashland City, TN ©2003
SBD TANK TYPE HEATERS
SERVICE HANDBOOK
VENTING
EXAMPLE: To combine two 6" vents with an
8" vent, the area of a combined vent should be
one half area of two 6 inch vents (14 + 14)
plus area of 8 inch vent (50) or 78 sq. inches.
Referring to chart, 78 sq. inches require 10"
diameter vent.
Vent Size
5"
6"
7"
8"
9"
12
Area in Square
Inches
Vent Size
20
10"
28
12"
38
14"
50
16"
64
18"
Area in Square
Inches
79
113
154
201
254
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