22
Combustion Air Termination--Ventilated Combustion Air
Option
Combustion air is piped directly to the burner box on furnace
using the same materials used to vent the furnace. (See Table 5.)
The combustion air pipe is terminated in an attic or crawl space
that is well ventilated with outdoor air and is well isolated from
the living space or garage. If the furnace is installed in a well
ventilated attic, the combustion air pipe can be terminated in the
same space. Refer to the Air for Combustion and Ventilation --
Ventilated Combusion Air Option Section in these instructions.
The combustion air pipe cannot be terminated in attics or
crawlspaces that use ventilation fans designed to operate during
the heating season. If ventilation fans are present in these areas,
the combustion air pipe must terminate outdoors as a Direct
Vent/2--Pipe system.
NOTE
: Combustion air pipe must have the same diameter as
vent pipe.
Attic terminations require at least (1) 90 degree elbow, with the
open end pointing horizontally or downward. The open end of
the elbow must be at least 12--inches above any insulation or
other materials. Screen the elbow with a wire mesh screen no
smaller than 3/8--inch square. (See Fig. 27.)
Crawlspace termination requires the open end of the pipe
pointing downward. Maintain 3--inches of clearance below the
floor joist insulation and 12--inches above the grade. Screen the
elbow with a wire mesh screen no smaller than 3/8--inch square.
(See Fig. 28 and 29.)
AIR FOR COMBUSTION AND VENTILATION --
Ventilated Combustion Air Option
Provisions for adequate combustion, ventilation, and dilution air
must be provided in accordance with:
U.S. Installations: Section 9.3 of the NFGC, Air for Combustion
and Ventilation and applicable provisions of the local building
codes.
Canadian Installations: Part 7 of the NSCNGPIC, Venting
Systems and Air Supply for Appliances and all authorities having
jurisdiction.
UNIT CORROSION HAZARD
Air for combustion must not be contaminated by
halogen compounds, which include fluoride, chloride,
bromide, and iodide. These elements may corrode heat
exchangers and shorten furnace life. Air contaminants
are found in aerosol sprays, detergents, bleaches,
cleaning
!
WARNING
This furnace requires OUTDOOR AIR for combustion.
CARBON MONOXIDE POISONING HAZARD
The operation of exhaust fans, kitchen ventilation fans,
clothes dryers, attic exhaust fans or fireplaces could create a
NEGATIVE PRESSURE CONDITION at the furnace.
Make--up air MUST be provided for the ventilation devices,
in addition to that required by the furnace. Refer to the
Carbon Monoxide Poisoning Hazard warning in the venting
section of these instructions to determine if an adequate
amount of make--up air is available.
!
WARNING
CARBON MONOXIDE POISONING HAZARD
Failure to supply outdoor air via grilles, louvers or vents
could result in death and/or personal injury. Many homes
require air to be supplied from outdoors for furnace
combustion, ventilation, and dilution of flue gases.
The furnace combustion air supply must be provided in
accordance with this instruction manual.
!
WARNING
An attic or crawlspace may be considered a space that freely
communicates with the outdoors provided there are adequate
permanent ventilation openings directly to outdoors having free
area of at least 1--in.2/4,000 Btuh of total input rating for all gas
appliances in the space.
NOTE
: In determining the free area of an opening, the blocking
effect of the louvers, grilles, and screens must be considered. If
the free area of a louver or grille design is unknown, it may be
assumed that wood louvers have a 20 percent free area, and metal
louvers or grilles have a 60 percent free area. Screens, when used,
must not be smaller than 1/4--in. mesh. Louvers and grilles must
be constructed so they cannot be closed.
58U
VB
