Carrier PG95ESA Installation, Start-Up, Operating And Service And Maintenance Instructions page 33

Ventilated Combustion Air Systems
In a ventilated combustion air option, the vent terminates and
discharges the flue products directly to the outdoors similar to a
direct vent system. See Fig. 42 for references to clearances required
by National code authorities.
All air for combustion is piped directly to the furnace from a space
that is well ventilated with outdoor air (such as an attic or crawl
space) and the space is well isolated from the living space or
garage. Combustion air requirements for this option are the same as
the requirements for providing outside air for combustion for a
Fig. 39 - - Combustion Air and Vent Pipe Termination for Direct Vent (2- -Pipe) System
Fig. 40 - - Vent Pipe Termination for Non- -Direct Vent and Ventilated Combustion Air System
single pipe vent system. Refer to the "Air For Combustion and
Ventilation" Section.
Non-Direct Vent (1-pipe) System
In a non direct-vent (1-pipe) system, all air for combustion is taken
from the area adjacent to furnace, and all flue products are
discharged to outdoor atmosphere. Air for combustion must be
supplied as described in the Air For Combustion and Ventilation
Section. Do not use an abandoned chimney to supply outside air to
the furnace. See Fig. 42 for references to vent clearances required
by National code authorities.
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