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All installations and services must be performed by qualified service personnel.
17
Recommended materials for the combustion air duct are smooth, round, galvanized
steel duct or schedule 20 PVC pipe. The maximum intake duct length allowed is
equivalent to 40-feet of straight duct. Reduce this length by 6-feet for the intake hood
and each 90-degree elbow used, and by 3-feet for each 45-degree elbow used the
combustion air duct. ?
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? CAUTION: Flexible, spiral, or corrugated duct is not
recommended, due to the relatively high-pressure drop associated with air movement
through this type of passageway.
Optional combustion air- a 4” round duct may be used by connecting a 3 x 4 reducer to
the 3” flex duct supplied with the furnace.
Figure 6