41
Combustion Quality
Combustion quality can be affected by several factors. Major
factors are venting and draining.
Venting
The venting system sould be planned and installed with the
following in mind:
•
Should not be longer than necessary
•
Use 45° elbows rather than 90° elbows when possible
•
Must not sag or otherwise trap condensate
•
Use longest radius fittings possible
•
If using 3" venting, make the transition from 2" to 3" as
close as practically possible
•
Make sure there is no flue gas recirculation into the
combustion air pipe
Condensate Drainage
Furnace combustion can be affected if a furnace is holding
condensate. Check for proper connections of drain hoses;
make sure furnace condensate trap is clean. Make sure
furnace is not improperly sloped. Make sure air conditioning
coil drain is not interfering with furnace drain.
Other Causes
1. Manifold Gas Pressure must be set, the gas being used,
Natural or L.P., high and low firing rates. If converted to
L.P. gas, check size of all orifices.
2. Remove Draft Inducer, Check the integrity of the gasket
between the inducer and the collector box cover, any air
leak here will have a negative effect on combustion. Check
the orifice hole in the collector box, it must be free or burrs
on both sides.
3. Make sure burners are clean, not out of position and line
up correctly with heat exchanger tubes, including the heat
exchanger orifice plate - this is the plate which mounts to
the front panel of the heat exchanger between the burners
and the heat exchanger tubes, make sure it is not loose,
missing a screw or hanging down between the burners and
heat exchanger causing flame impingement.
4. Make sure the field installed gas line is not binding and
causing distortion of burner assembly.
5. If the furnace is installed as a one pipe system; make sure
the surrounding area and structure are adequate to provide
combustion air.
6. Make sure there are no cabinet air leakes allowing supply
air to affect combustion.
7. If heat exchanger integrity is uncertain, follow procedures
in Service Bulletin SF-041.
