905.6 Duct Furnaces Used with Refrigeration Sys-

tems. A duct furnace shall not be installed in conjunction with a refrigeration coil where circulation of cooled air is provided by the blower. Exception: Where the blower has sufficient capacity to overcome the external static resistance imposed by the duct system, furnace, and the cooling coil and the air throughput necessary for heating or cooling, whichever is greater. [NFPA 54:10.10.6.1]

905.6.1 In Conjunction with Cooling Appliances. Duct furnaces used in conjunction with cooling appliances shall be installed in parallel with or on the upstream side of cooling coils to avoid condensation within heating elements. With a parallel flow arrangement, the dampers or other means used to control the flow of air shall be sufficiently tight to prevent any circulation of cooled air through the unit. Exception: Where the duct furnace has been specifically listed for downstream installation. [NFPA 54:10.10.6.2]

905.6.2 Located Upstream from Cooling Coils. Where duct furnaces are to be located upstream from cooling units, the cooling unit shall be so designed or equipped as to not develop excessive temperatures or pressures. [NFPA 54:10.10.6.3] 905.6.3 Heat Exchangers. Where a duct furnace is installed downstream of an evaporative cooler or air washer, the heat exchanger shall be constructed of corro

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been specifically listed for downstream installation. With a parallel flow arrangement, the dampers or other means used to control flow of air shall be sufficiently tight to prevent any circulation of cooled air through the furnace. (4) Means shall be provided for disposal of condensate and

to prevent dripping of condensate on the heating element.

[NFPA 54:10.3.8]