10
AIR FOR COMBUSTION AND
VENTILATION
Introduction
Direct Vent (2--pipe) Applications
When the furnace is installed as a direct vent (2-pipe) furnace, no
special provisions for air for combustion are required. However,
other gas appliances installed in the space with the furnace may
require outside air for combustion. Follow the guidelines below to
insure that other gas appliances have sufficient air for combustion.
Ventilated Combustion Air Applications
When the furnace is installed using the ventilated combustion air
option, the attic or crawlspace must freely communicate with the
outdoor to provide sufficient air for combustion. 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.
All air for combustion is piped directly to the furnace from a space
that is well ventilated with outdoor air (such as an attic, crawl
space, or equipment closet) and the space is well isolated from the
living space or garage. In addition, other gas appliances installed
in the space with the furnace may require outside air for
combustion. Follow the guidelines below to insure that the roof or
crawlspace walls have sufficient free area to provide sufficient air
for combustion and ventilation for the furnaces. The guidelines
below can be used to insure that other gas appliances have
sufficient air for combustion.
Provisions for adequate combustion, ventilation, and dilution air
must be provided in accordance with:
S
U.S.A. Installations: Section 9.3 of the NFPA 54/ANSI
Z223.1--2012 , Air for Combustion and Ventilation and
applicable provisions of the local building codes.
S
Canada: Part 8 of the CAN/CSA--B149.1--2010, Venting
Systems and Air Supply for Appliances.
FURNACE CORROSION HAZARD
Failure to follow this caution may result in furnace damage.
Air for combustion must not be contaminated by halogen
compounds, which include fluoride, chloride, bromide, and
iodide. These elements can corrode heat exchangers and
shorten furnace life. Air contaminants are found in aerosol
sprays, detergents, bleaches, cleaning solvents, salts, air
fresheners, and other household products.
CAUTION
!
CARBON MONOXIDE POISONING HAZARD
Failure to follow this warning could result in personal
injury or death.
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
Outdoor Combustion Air Method
1. Provide the space with sufficient air for proper combustion,
ventilation, and dilution of flue gases using permanent hori-
zontal or vertical duct(s) or opening(s) directly communicat-
ing with the outdoors or spaces that freely communicate
with the outdoors.
2.
Fig.
6 illustrates how to provide
TWO OUTDOOR
OPENINGS
, one inlet and one outlet combustion and vent-
ilation air opening, to the outdoors.
a. One opening
MUST
commence within 12 in. (300 mm)
of the ceiling and the second opening MUST commence
within 12 in. (300 mm) of the floor.
b. Size openings and ducts per Fig. 6 and Table 3.
c.
TWO HORIZONTAL DUCTS
require 1 sq. in. (645 sq.
mm) of free area per 2,000 Btuh (1,100 mm
2
/kW) of com-
bined input for all gas appliances in the space per Fig. 6 and
Table 3.
d.
TWO OPENINGS OR VERTICAL DUCTS
require 1
sq. in. (645 sq. mm) of free area per 4,000 Btuh (550
mm
2
/kW) for combined input of all gas appliances in the
space per Fig. 6 and Table 3.
3.
ONE OUTDOOR OPENING
requires:
a. 1 sq. in. (645 sq. mm) of free area per 3,000 Btuh (734
mm
2
/kW) for combined input of all gas appliances in the
space per Fig. 6 and Table 3.
b. Not less than the sum of the areas of all vent connectors in
the space.
The opening shall commence within 12 in. (300 mm) of the
ceiling. Appliances in the space shall have clearances of at least 1
in. (25 mm) from the sides and back and 6 in. (150 mm) from the
front. The opening shall directly communicate with the outdoors or
shall communicate through a vertical or horizontal duct to the
outdoors or spaces (crawl or attic) that freely communicate with the
outdoors.
987MA
