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V. Combustion Air Supply
The duct furnace needs an ample supply of air for proper and safe combustion of the fuel gas.
Do not block or obstruct
air openings to the area where the heating unit is installed.
Locate unit to insure an adequate supply of fresh air to
replace air used in the combustion and ventilation process.
For outdoor applications and for indoor applications where the combustion air is drawn from the surrounding space
,
openings for combustion air must be provided in a panel or door
with direct access to the vestibule area where the
burners and draft inducer are located.
Air opening(s)
must be sized to provide a suitable supply of air for combustion to
the burner compartment and have a
minimum free area of 1 sq. in.
(625mm
2
) per
4,000 Btuh
(2,345 W) of rated input for
total input. The minimum dimension of any air opening should not be less than 3 inches.
All fresh air openings
must be in
accordance with the National Fuel Gas Code ANSI Z223.1 (NFPA 54) in the United States and Can/CGA-B149 Installation
Code in Canada. The air handling unit must be installed so that access to air inlet openings is unobstructed. For louvered
doors be sure to provide a suitable windbreak to prevent wind driven rain and snow from collecting in the vestibule area
and on electrical components.
For indoor installations
, locate heating unit to insure an adequate supply of fresh air to replace air used in the combustion
and ventilation process. Air must also enter the appliance location to replace the air exhausted through the vent system.
Refer to installation codes for specific requirements and guidelines.
For indoor applications where combustion air is taken from outside the heated space (
Separated Combustion Systems
)
refer to Section VI Venting.
VI. Venting - General
Safe operation of indirect-fired gas furnaces requires a properly operating vent system which exhausts
all the products of combustion (flue gases) to the outside atmosphere.
Venting must be in accordance with local codes and the National Fuel Gas Code NFPA54 / ANSI Z223.1 in the United States
or CAN/CSA B149.1 Natural and Propane Installation Code in Canada. Local requirements typically supersede national
requirements.
EM Series duct furnaces are listed as Category II and IV heaters
. Category II furnaces operate with a negative vent
pressure and vent gas temperatures typically less than 150 oF. Category IV furnaces operate with a positive vent pressure
and vent gas temperatures typically less than 150 oF. The venting system must be gas tight and water tight. Proper
installation of the vent system must also assure drainage of condensate to prevent deterioration of the vent system.
The vent piping must be exclusive to a single furnace.
Do not use dampers in vent pipes. All pipe openings external to
building must have a protective screen installed.
For gas furnaces incorporating two (2) inducer draft fans, all guidelines/ recommendations by the manufacturer are
to be followed for each individual exhaust vent.
Exhaust vent ducting must NOT be joined (no common flue).
Vent pipe used for this duct furnace may be Schedule 40 PVC pipe or vent pipe listed to UL 1738 or ULC S636
. All
field installed vent pipe and fittings must be from the same manufacturer. DO NOT intermix vent system parts from different
vent manufacturers. All furnaces include a vent connector/ couplings for attachments of the vent pipe. Minimum length before
any turns in pipe is 12”. In Canada, the PVC vent pipe must be approved to ULC S636.
To ensure that piping is leak free after installation,
PVC sections must be solvent welded (glued) consistent with
industry standards and applicable local codes.
Primer and cement for joints must conform to applicable ASTM standards.
WARNING !
Failure to provide proper venting affects furnace performance and may result
in a health hazard which could cause serious personal injury or death.
