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DUCTING
PRIMARY FURNACE
To install the GBU070 as a “Primary Furnace” first locate the furnace as near the chimney
and as centralized with respect to heat distribution as practical. Follow all clearance to
combustible requirements. Connect the ductwork to the furnace. Minimum supply plenum
size: 14” x 14”, minimum return plenum size: 12” round. When a furnace is installed so
that supply ducts carry air circulated by the furnace to the areas outside the space
containing the furnace, the return air must also be handled by a duct sealed to the furnace
casing and terminating outside the space containing the furnace. Where there is no
complete return duct system, the return connection must be run full size to a point outside
the furnace room. Air duct systems should be installed in accordance with standards for air
conditioning systems. NFPA Pamphlet #90. They should be sized in accordance with ACCA
Manual D or whichever is applicable, after completing installation as per the appropriate
section of this manual.
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