Replacing a 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
surrounding 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
temperature falls below its dew point temperature . A more
efficient 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 be reduced, and more 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
temperature, 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 must 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 . All models have a
piped combustion chamber condensate drain, and Models 032
through 200 have a rear inspection cover that provides access
to the drain line .
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
condensate mentioned above . The drip shield below the rear
cleanout port must be correctly installed as shown in the
following section .
Rear Inspection Cover
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 (see
). 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 underside of the tube and into the unit or down the
side of the rear panel .
NOTE:
Note: If an excessive amount of condensate is
dripping out of the rear inspection cover, check
the condensate drain for blockage and clean if
necessary . Check the Rear Condensate Drain
annually for blockage .
Figure 18:
Inspection Cover
3
1
2
4
2
3
1
Service
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IM 684-6 • ROOFTOP SYSTEMS
