7
Direct Vent Installation
This condensing furnace is certified for installation as a
Direct Vent (2-pipe) appliance. Direct Vent (2-pipe) furnaces
draw combustion air directly from the outdoors and then
vent the combustion products back outside, isolating the
entire system from the indoor space. It is important to make
sure that the whole system is sealed and clearances to
combustibles are maintained regardless of the installation
being in a confined or unconfined space. This section
specifies installation requirements for Direct Vent (2-pipe)
piping. Table 2 (page 8) contains the length of vent and
combustion air piping for this type of installation.
Provisions must be made during the installation of this
furnace that provide an adequate supply of fresh air for
combustion and ventilation. The combustion air from the
outside needs to be clear of chemicals that can cause
corrosion. The inlet pipe should not be placed near
corrosive chemicals such as those listed on page 5.
Air openings on top of the furnace and openings in closet
doors or walls must never be restricted. If the furnace is
operated without adequate air for combustion, the flame
roll-out switch will open, turning off the gas supply to the
burners.
NOTE
:
This safety device is a manually reset
switch.
DO NOT install jumper wires across these
switches to defeat their function or reset a switch
without identifying and correcting the fault condition.
If
a switch must be replaced, use only the correct sized part
specified in the Replacement Parts List provided online.
Vent Pipe Length & Diameter
For proper furnace operation, the combustion air and vent
piping must not be excessively restrictive.
• The venting system should be designed to have the
minimum number of elbows or turns.
• All horizontal runs must slope upwards from the furnace
at 1/4 inch minimum per running foot of vent.
• Transition to the final vent diameter should be done as
close to the furnace outlet as practical.
• Always use the same size or a larger pipe for combustion
air that is used for the exhaust vent.
Table 2 (page 8) indicates the maximum allowable pipe
length for a furnace of known input rate, when installed
with piping of selected diameter and number of elbows. To
use the table, the furnace input rate, the centerline length
and the number of elbows on each pipe must be known.
When estimating the length of vent runs, consideration
must be made to the effect of elbows and other fittings.
This is conveniently handled using the idea of “equivalent
length”. This means the fittings are assigned a linear length
that accounts for the pressure drop they will cause. For
example: a 3” diameter, long radius elbow is worth the
equivalent of 3.5 feet of linear run.
The equivalent lenghts of tees and various elbows are
listed in Table 2. Measure the linear length of your vent run
and then add in the equivalent length of each fitting. The
Important Information
WARNING:
Furnace installation using methods other than
those described in the following sections must
comply with the National Fuel Gas Code (NFGC)
and all applicable local codes.
WARNING:
Upon completion of the furnace installation,
carefully inspect the entire flue system both
inside and outside the furnace to assure it is
properly sealed. Leaks in the flue system can
result in serious personal injury or death due
to exposure of flue products, including carbon
monoxide.
WARNING:
This furnace must not be vented with other
appliances, even if that appliance is of the
condensing type. This includes water heaters
of any efficiency. Common venting can result
in severe corrosion of other appliances or their
venting and can allow combustion gases to
escape through such appliances or vents. Do
not vent the furnace to a fireplace chimney or
building chase.
• This furnace must be vented in compliance with
the current revision of the National Fuel Gas Code
(ANSI-Z223.1/NFPA54). Instructions for determining
the adequacy of combustion air for an installation
can be found in the current revision of the NFGC
(ANSI Z223.1 / NFPA54).
Consult local codes for
special requirements
. These requirements are for
US installations as found in the NFGC.
• The requirements in Canada (B149.1) are structured
differently. In Canada, venting shall conform to the
requirements of the current (CAN/CGA B149.1 or .2)
installation codes.
Consult local codes for special
requirements.
Category IV Appliances
This furnace is classified as a “Category IV” appliance,
which requires special venting materials and installation
procedures.
Category IV appliances operate with positive
vent pressure and requires thoroughly sealed vent systems.
They also produce liquid condensate, which is slightly
acidic and can cause severe corrosion of ordinary venting
materials. Furnace operation can be adversely affected
by restrictive vent and combustion air piping.
