1. There must be a minimum clearance of 1 in. on all sides of the supply air duct for the first 3 ft of the duct for 20 kW and 25 kW heaters (0 in. thereafter). For all other
heaters, there must be a 0 in. clearance on all sides for the entire length of the supply air duct.
2. Units must be installed outdoors. Overhanging structures or shrubs must not obstruct the outdoor air discharge outlet.
3. Units can be installed on combustible materials made from wood or class A, B, or C roof covering materials if factory base rails are left in place as shipped.
Note: For units with a roof curb, the minimum clearance between combustible roof curb material and the supply air duct can be reduced from 1 in. to 1/2 in.
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