Specifications

IM 685-2 19
3. Excessive Condensation - Applications which will pro-
duce condensation require an all stainless steel heat
exchanger that is resistant to the effects of this condensa-
tion and that will give long heat exchanger life. The like-
lihood of condensation increases with:
a. Colder supply air temperature across the secondary
tubes, as on units taking in a lot of outdoor air in
colder weather.
b. Lower heat flow through the secondary tubes, as on
modulating burners when operating at reduced input.
c. High airflow across the secondary tubes such as any
application with a low temperature rise furnace.
4. Chemical Deterioration - Refrigerant leaks, some aero-
sol can propellants, fumes from dry cleaning establish-
ments, beauty shops, swimming pools, and others, often
have detrimental effects on heat exchangers when they
get into the combustion air supply and thereby into the
combustion. Even fumes from nearby roof exhaust fans
can cause problems.
5. Inadequate or Distorted Airflow - Internal baffles that
have been repositioned or have loosened up and moved
can distort the airflow and cause failures. Construction
rubbish, shipping cartons, and insulation that has come
loose will occasionally end up inside a unit and block air-
flow to part of the furnace, resulting in a failure. These
items can also alter the air or heat flow to the fan limit or
some other control and contribute to a failure.
Replacing Heat Exchanger
1. Remove the complete flue box, the casing panel through
which the flue tubes pass, and the rear inspection cover.
Open the hinged rear door.
2. The burner is mounted on and supported by the heat
exchanger studs with four nuts. When removing the heat
exchanger, the burner must either be removed or blocked
in place. Remove the four burner mounting nuts and the
two exchanger bolts located 2" above the upper burner
mounting nuts.
3. When it is necessary to remove any air baffles surround-
ing the heat exchanger, carefully note the locations and
clearances of these baffles before removing them so they
can be replaced in the exact same position.
4. Remove the two bottom bolts at the back of the heat
exchanger.
5. Withdraw the heat exchanger through the back of the casing.
Furnace Condensation
A furnace will produce condensation when the flue gas tem-
perature falls below its dew point temperature. A more effi-
cient furnace will transfer more of its heat into the building,
and leave less heat in the flue gas. This results in a lower flue
gas temperature and more condensate.
A modulating burner will produce more condensate than an
on-off burner. As the firing rate of the burner is reduced the
flue gas temperature will he reduced, and if it is reduced
below its dew point condensate will be produced.
A furnace that is heating a high percentage of outside air will
also produce more condensate. The colder the air contacting
the heat exchanger, the lower the resulting flue gas tempera-
ture, and consequently the more condensate.
Do not think a furnace has a problem because it produces
condensate anymore than you would think a cooling coil has
a problem because it produces condensate. However suitable
steps should be taken to manage the flow of the condensate
produced.
Most condensate will be produced in the secondary tubes
where flue gas will sweep it into the flue box. Condensate
will also come from the combustion chamber. Models 020
and 025 have a piped combustion chamber condensate drain,
and Models 032 through 200 have a rear cleanout port with
an integral condensate drain.
Condensate will also drip from the drains in the two outer
corners of the flue box, and from the drip shield below the
rear cleanout port. Condensate should not be running down
the unit, except at times the wind may blow the dripping con-
densate mentioned above. The drip shield below the rear
cleanout port must be correctly installed as shown in the fol-
lowing section.
Rear Inspection Cover (see Figure 15)
The rear inspection cover is equipped with a stainless steel
drip shield to keep condensate away from the side of the unit
if condensate drips out of the inspection cover. The shield (1)
must fit snugly against the bottom of the cleanout port tube
(2) at (3) so condensate (4) cannot run back along the under-
side of the tube and into the unit or down the side of the rear
panel.
Note: If an excessive amount of condensate is dripping
out of the rear inspection cover, check the conden-
sate drain for blockage and clean if necessary.
Check the Rear Condensate Drain annually for
blockage.
Figure 15. Inspection Cover (Models 032 thru 200)
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