All installations and services must be performed by qualified service personnel.
The preferred location of the outside combustion air intake termination (e.g. an optional stainless steel intake hood, part no.370183) is through the side of the structure, skirting or enclosure. An alternate termination location is under the structure in the skirted or crawlspace area providing a minimum of 50 square inches of free area exists around the perimeter for outside combustion air to be drawn through. NOTE: Combustion air cannot be drawn from the occupied space of the home.
The furnace is shipped with a combustion air duct that must be installed in the bottom of the burner enclosure, before the burner is installed. This 2-inch by 7-inch duct is shipped in two pieces. High temperature silicone sealant should be applied to both vertical seams, before it is snapped together with four flanges on one end. The duct must then have high temperature silicone applied to the flanges. Then, the combustion air duct can be inserted through the opening in the floor base model no.70. When the combustion air duct has been inserted completely, secure the duct to the combustion adapter with self-tapping sheet metal screws, refer to Figure 6. Make certain that the flanges, duct, and adapter are completely sealed to the burner enclosure base with high temperature silicone caulk.
NOTE: The adapter may be cut with sheet metal shears to the appropriate size and secured over the inlet air duct opening. The adapter will convert the rectangular opening to a round connector ring. The ring will allow the connection of 2-inch I.D. flexible hose (provided) between the adapter and the inlet air boot, attached to the burner. Secure both ends of the flex hose with hose clamps (provided).
A2-inch round to 7-inch x 4-inch rectangular, sheet metal, transition boot is supplied with the furnace for adapting a 4-inch round combustion air duct to the 2-inch x 7-inch combustion air duct. This boot has a screen inserted into the 4-inch round portion of the boot to provide a degree of protection from pests entering the furnace when the boot is terminated in the crawl space, or skirted area, directly below the furnace.
The material recommended for the combustion air duct is smooth, round, galvanized steel duct or schedule 20 PVC pipe. The maximum 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. Flexible, spiral, or corrugated duct is not recommended, due to the relatively high pressure drop associated with air movement through this type of passageway.
