14
Condensation
These furnaces are not intended to have condensa-
tion occur in the furnace or in the venting system.
Such condensation can cause corrosion and
premature failure of the vent system, leading to
possible asphyxiation. In most cases, condensation
is a result of an oversized vent system. When sizing
the vent system for this furnace, the vent pipe size
should be kept to the minimum allowable according
to the vent tables in the National Fuel Gas Code.
Where local experience indicates that condensation
may be a problem, the following steps should be
taken:
1. Usage of single-wall vent pipe should kept to a
minimum and should never be used in any un-
heated space.
2. As noted above, all masonry chimneys must be
lined with the liner sized no larger than is neces-
sary for the capacity of the attached appliances.
3. If local codes permit, the outside of metal vent
pipe may be insulated with a noncombustible
insulating material.
4. If necessary, the furnace-circulating blower may
be set to a lower speed, which will raise the flue
temperature slightly. However, the temperature
rise across the furnace must not exceed the
maximum listed in the specification table in
these instructions and on the furnace rating
plate.
In certain conditions, condensation in a lined
masonry chimney may be unavoidable. In such
cases, provisions must be made to drain off and
dispose of condensate to avoid damage to the
chimney.
Further Instructions
For more details on venting or other aspects of gas
appliance installation, consult the NATIONAL FUEL
GAS CODE, ANSI Z223.1. In Canada, consult the
CAN/CGA-B149 Installation Code. It is highly
recommended that all gas appliance installers and
servicemen have a copy of this manual.
Replacement of Existing Furnace on
Common Vent System
When this furnace is installed as a replacement for
an old furnace, which is common vented with a
water heater or other gas appliance, and the new
furnace is no longer connected to the common
venting system, the common vent system may be
too large for the appliances remaining on the vent
system after the old furnace is removed. To test for
an oversized vent system, the following steps shall
be followed with each appliance remaining con-
nected to the common venting system placed in
operation, while the other appliances remaining
connected to the common venting system are not in
operation:
1. Seal any unused openings in the common
venting system.
2. Visually inspect the venting system for proper
size and horizontal pitch and determine that
there is no blockage or restriction, leakage, cor-
rosion or other deficiencies which could cause
an unsafe condition.
3. Insofar, as is practical, close all building doors
and windows and all doors between the space in
which the appliances remaining connected to
the common venting system are located and
other spaces of the building. Turn on clothes
dryers and any appliance not connected to the
common venting system.
Turn on any exhaust fans, such as range hoods
and bathroom exhausts, so they will operate at
maximum speed. Do not operate a summer ex-
haust fan. Close fireplace dampers.
4. Follow the lighting instructions. Place the
appliance being inspected in operation. Adjust
thermostat so appliance will operate continu-
ously.
5. Test for spillage at the draft hood relief opening
after five minutes of main burner operation. Use
the flame of a match or candle, or smoke from a
cigarette, cigar, or pipe.
6. After it has been determined that each appliance
remaining connected to the common venting
system properly vents when tested as outlined
above, return doors, windows, exhaust fans,
fireplace dampers, and any other gas-burning
appliance to their previous condition of use.
7. If improper venting is observed during any of the
above tests, the common venting system must
be corrected. Any changes to the venting sys-
tem must be in accordance with the National
Fuel Gas Code, ANSI Z223.1. In Canada, any
changes to the venting system must be in ac-
cordance with the latest edition of the
CAN/CGA-B149 Installation Codes and applica-
ble local codes. If any portion of the common
venting system must be resized, it should be
resized to approach the minimum size as deter-
mined using the appropriate tables in Appendix
G in the National Fuel Gas Code, ANSI Z223.1
or in Canada, the latest edition of the CAN/CGA-
B149 Installation Code.
