26
CARBON DEPOSITS
(SOOTING)
Key Takeaways: Sooting Fireplace Troubleshooting
✅ Common Causes of Sooting (Carbon Deposits):
-
Incorrect log placement
-
Improper primary air adjustment
-
Excessive ember material
-
Incorrect lava rock placement
-
Over-fired or under-fired appliance
-
Direct-venting issues (unsealed or blocked)
-
Leaking direct-vent gasket
-
Atmospheric effects on B-Vent and Insert models
-
Improper orifice alignment
-
Mismatched valve/orifice with fuel type
✅ Key Troubleshooting Steps:
-
Check Log Placement:
-
Logs must follow the installation instructions precisely.
-
Incorrect placement may restrict airflow, causing taller, yellow flames that lead to soot.
-
Clean sooty logs with a vacuum and soft brush.
-
-
Check Primary Air Shutters:
-
Factory-set but should be verified during installation.
-
Clear any debris in the air openings.
-
Propane requires more primary air than natural gas.
-
-
Check Orifice Alignment:
-
Orifice must be aligned perpendicular to the burner centerline.
-
Never drill out an orifice; replace if faulty.
-
Use pipe joint compound during reinstallation to prevent leaks.
-
-
Check Ember Fibers and Lava Rock Placement:
-
Ember fibers should be loose and fluffy (not compressed).
-
Lava rocks are decorative only and should never be placed on the burner.
-
-
Check Firing Rate:
-
Over-firing may cause soot, broken glass, and excessive temperatures.
-
Under-firing may result in low flames or incomplete combustion.
-
✅ Key Factors Governing Firing Rate:
-
Orifice size (refer to appliance rating plate)
-
Manifold pressure (check against appliance specs)
-
Gas type (natural gas vs propane)
✅ Gas Pressure Guidelines:
-
Natural gas manifold pressure: Typically 3.5" WC
-
Propane manifold pressure: Typically 10" WC (some older models may use 11")
-
Inlet pressure: Varies; check appliance rating plate for specifics
By methodically checking these factors, technicians can accurately diagnose and resolve soot-related issues in gas fireplaces.
Some conditions can guarantee the production of soot. In most cases incomplete combustion starts
with the inappropriate adjustment and setup of the appliance. However, several factors must be
considered when attempting to diagnose a sooting fireplace condition. Remember that two or more
of these factors could be involved.
• Is the log placement correct?
• Proper primary air adjustment for each burner
• Excessive ember material
• Improper placement of the lava rock
• Is the fireplace over or under fire?
• Direct-Venting not properly sealed or blocked
• Direct-Vent gasket leaking flue gas
• Atmospheric effects on B-Vent and Insert models
• Improper orifice alignment
• Valve and orifices not matched with fuel type
CHECK THE LOG PLACEMENT
Most logs in Empire Comfort Systems Inc. gas appliances are designed to be placed in a particular
pattern on the burner log grate. Any time flame touches a log it creates a condition called flame
impingement, which can cause sooting if the logs and burner are not designed for impingement.
Some models have been designed so that the front log (the larger log just behind the front portion
of the burner) will interact with the front burner to result in a glowing action. The front log is the
most sensitive when it comes to positioning. Aside from it being desirable for the front log to be
situated partially in the flame, it is critical that the air space between the burner and the log not be
completely blocked. Restricting or closing that gap will create a taller, yellow flame that, in extreme
conditions, may cause carbon.
It is important that the logs are arranged according to the installation instructions for each appliance
model. The logs have been designed with holes or flat spots with notches, depending on the model
you are working on. The logs are either numbered or have arrows that point towards the front
window. Refer to the installation instructions for proper placement. If you find signs of soot build-up
on the logs, the solution is most likely correcting the log placement. Remove any soot from logs with
a vacuum and a small paint brush.
CHECK THE PRIMARY AIR SHUTTERS
The primary air shutters are factory set, but it is good practice to check the settings at the time of
installation while consulting the manual for the correct setting. On any sooting call this should be the
first place to start. Also check for any type of debris in the primary air openings. In some instances
you may need to increase or decrease primary air depending on the type of installation. It is best to
consult the technical department before making these adjustments. Also keep in mind that propane
requires more primary air than natural gas.
CHECK ORIFICE ALIGNMENT
The burner orifice must be aligned perpendicular to the centerline of the burner housing. Never drill
out an orifice. In case of a problem a new one must be ordered. The proper orifice, factory drilled
and aligned, should allow the gas to shoot down the middle of the venturi, draw the correct volume of
primary air and allow the air and gas to mix properly for combustion. When reinstalling an orifice, use
pipe joint compound and do not cross thread it into the gas manifold, as leakage and misalignment
will occur. Always use a back-up wrench when removing or installing an orifice.
EMBER FIBERS, CERAMIC FIBERS, AND LAVA ROCK PLACEMENT
Ember fibers are used on most fireplaces. If compressed and packed onto the burner, they may cause
incomplete combustion. Keep the burner portholes free by placing the embers in a loose and fluffy
manner. Always try and keep the pieces about the size of a dime. These embers can also be rubbed
into the logs to add a glowing effect where the flame impinges the log. When replacing existing ember
material it is always best to use a small brush or vacuum to clean off the burner first before placing new
embers.
Lava rocks are used for decorative purposes ONLY and must not be placed on any part of the burner.
Lava rocks should only be placed on the bottom of the firebox around the burner assembly. Be careful
that they do not interrupt airflow into the primary air inlets for the burner.
Gloves are recommended when handling logs to prevent skin irritation. Logs are fragile - Handle
with care.
DETERMINING THE CORRECT FIRING RATE: IS THE APPLIANCE OVER-FIRED
OR UNDER-FIRED?
All gas appliances need fuel and air for the combustion process. A balance between fuel and air has
been established for each appliance. If the amount of fuel to the burner is too great you will possibly
experience sooting and other cosmetic symptoms. If insufficient fuel is combusted, you will possibly
observe a low flame condition. For under-fired conditions with the correct manifold pressure, it will be
necessary to remove the orifice and inspect for burrs or debris caught in the orifice opening.
The three factors that govern the fireplace firing rate are:
1. Orifice size
2. Manifold pressure
3. Gas type
ORIFICE SIZE IDENTIFICATION
The correct orifice size(s) for each appliance can be found on the rating plate. The orifice size is
identified by locating the orifice number stamped onto the orifice brass body. If you are unable to read
this number, the size can be determined using a drill index set.
CAUTION: Over-firing an appliance may cause soot production, broken glass, discolored trim, valve
damage and excessive temperatures and may result in personal and property damage.
GAS PRESSURE
Fireplaces and stoves operate at different manifold pressures and may also require differing inlet
pressures, so always check the appliance rating plate for the correct inlet and manifold pressures.
While the manifold pressure for Natural is typically 3.5” WC, minimum inlet pressures may be
anywhere from 4.5” to 7” WC, depending on the appliance. For Propane, manifold pressure is now
10” WC, while some older products operated at 11” WC. Inlet pressure for Propane is typically around
14” WC.
