9
ALWAYS the nominal capacity of the outdoor
unit. In some cases the nominal system
capacity is not the same as the nominal capacity
of the indoor coil.
Selecting the AC Cooling Airfl ow
A/C cooling is referred to in the User’s manual of
the IQ Drive Programmable thermostat.
Selecting the Heating Airfl ow
Furnace temperature rise depends on airfl ows
rate. To select the air fl ow, enter the program-
ming screen on the IQ thermostat. Select the
furnace input rate and then select the desired
temperature rise (see Table 1).
NOTE:
To set too high temperature rise of the
furnace may result in air limit operation.
VENTING AND COMBUSTION AIR
REQUIREMENTS
These condensing furnaces may be installed
with outdoor combustion air piped directly to the
furnace, or without such special piping. Codes
refer to the former as “direct vent” or “two pipe”
installation. Installation with air taken from around
the furnace is sometimes referred to as “one
pipe” installation - i.e. only the vent (exhaust)
pipe is provided.
Provisions must be made for adequate sup-
ply of air for combustion and ventilation. For
United States installations, the adequacy of air
provisions can be determined by consulting the
current version of the National Fuel Gas Code
(ANSI Z223.1/NPFA-54). For Canadian installa-
tions, requirements are specifi ed in the National
Standard of Canada (CAN/CGA B149.1 & .2).
Consult local codes for special requirements.
An important consideration in selecting one or
two pipe installation is the quality of the combus-
tion air. Indoor air is sometimes contaminated
with various household chemicals which can
cause severe corrosion in the furnace combus-
tion system.
NOTE:
If the furnace is operated without ad-
equate air for combustion and ventilation, it may
not perform properly. Furnace components may
be strained by high temperature and could fail
prematurely.
WARNING:
Furnace installation using methods
other than those described in the fol-
lowing sections must comply with the
National Fuel Gas Code and all appli-
cable local codes to provide suffi cient
combustion air for the furnace.
Combustion Air Quality
The recommended source of combustion air is
to use the outdoor air supply. However, the use
of indoor air in most applications is acceptable
except as follows:
1. If the furnace is installed in a confi ned
space it is recommended that the necessary
combustion air come from the outdoors by
way of attic, crawl space, air duct, or direct
opening.
2. If outdoor combustion air is used, there
must be no exposure to the installations or
substances listed in Item 3 below.
3. The following types of installation may re-
quire
Outdoor Air
for combustion, due to
chemical exposures:
•
Commercial
buildings
• Buildings with indoor pools
• Furnaces installed in laundry rooms
• Furnaces installed in hobby or craft
rooms
• Furnaces installed near chemical storage
areas
Exposure to the following substances in
the combustion air supply may also require
Outdoor Air
for combustion:
• Permanent wave solutions
• Chlorinated waxes and cleaners
• Chlorine based swimming pool chemi-
cals
• Water softening chemicals
• De-icing salts or chemicals
• Carbon
tetrachloride
• Halogen
type
refrigerants
• Cleaning solvents (such as perchloroethy-
lene)
• Printing inks, paint removers, varnishes,
etc.
• Hydrochloric
acid
• Cements
and
glues
