7/95 ATTACHMENT 1 RULE 74.15.1: 8

ATTACHMENT 1

Equipment Tuning Procedure

for Forced Draft-fired Equipment1

Nothing in this Equipment Tuning Procedure shall be construed to require any act or omission 

that would result in unsafe conditions or would be in violation of any regulation or requirement 

established by Factory Mutual, Industrial Risk Insurers, National Fire Prevention Association, the 

California Department of Industrial Relations (Occupational Safety and Health Division), the 

Federal Occupational Safety and Health Administration, or other relevant regulations and 

requirements.

1. Operate the unit at the firing rate most typical of normal operation. If the unit 

experiences significant load variations during normal operation, operate it at its average 

firing rate.

2. At this firing rate, record stack gas temperature, oxygen concentration, and CO 

concentration (for gaseous fuels) or smoke-spot number2(for liquid fuels), and observe 

flame conditions after unit operation stabilizes at the firing rate selected. If the excess 

oxygen in the stack gas is at the lower end of the range of typical minimum values3, and if 

the CO emissions are low and there is not smoke, the unit is probably operating at near 

optimum efficiency - at this particular firing rate. However, complete the remaining 

portion of this procedure to determine whether still lower oxygen levels are practical.

3. Increase combustion air flow to the furnace until stack gas oxygen levels increase by one 

to two percent over the level measured in Step 2. As in Step 2, record the stack gas 

temperature, CO concentration (for gaseous fuels) or smoke-spot number (for liquid 

fuels), and observe flame conditions for these higher oxygen levels after boiler operation 

stabilizes.

4. Decrease combustion air flow until the stack gas oxygen concentration is at the level 

measured in Step 2. From this level gradually reduce the combustion air flow, in small 

increments. After each increment, record 

 

1

. This tuning procedure is based on a tune-up procedure developed by KVB, Inc. for the 

EPA.

2

. The smoke-spot number can be determined with ASTM Test Method D-2156 or with the 

Bacharach method.

3

. Typical minimum oxygen levels for boilers at high firing rates are:

1. For natural gas: 0.5% - 3%

2. For liquid fuels: 2% - 4%
7/95 ATTACHMENT 1 RULE 74.15.1: 9

the stack gas temperature, oxygen concentration, CO concentration (for gaseous fuels) 

and smoke-spot number (for liquid fuels). Also observe the flame and record any 

changes in its condition.

5. Continue to reduce combustion air flow stepwise, until one of these limits in reached:

a. Unacceptable flame conditions - such as flame impingement on furnace walls or 

burner parts, excessive flame carryover, or flame instability.

b. Stack gas CO concentrations greater than 400 ppm.

c. Smoking at the stack.

d. Equipment-related limitations - such as low windbox/furnace pressure differential, 

built in air-flow limits, etc.

6. Develop an 02/CO curve (for gaseous fuels) or 02/smoke curve (for liquid fuels) similar 

to those shown in Figures 1 and 2 using the excess oxygen and CO or smoke-spot number 

data obtained at each combustion air flow setting.

7. From the curves prepared in Step 6, find the stack gas oxygen levels where the CO 

emissions or smoke-spot number equal the following values:

Fuel Measurement Value

Gaseous CO Emissions 400 ppm

#1 & #2 oils smoke-spot number number 1

#4 oil smoke-spot number number 2

#5 oil smoke-spot number number 3

Other oils smoke-spot number number 4

The above conditions are referred to as CO or smoke threshold, or as the minimum excess 

oxygen level.

Compare this minimum value of excess oxygen to the expected value provided by the 

combustion unit manufacturer. If the minimum level found is substantially higher than 

the value provided by the combustion unit manufacturer, burner adjustments can probably 

be made to improve fuel and air mixing, thereby allowing operation with less air.

8. Add 0.5 to 2.0 percent to the minimum excess oxygen level found in Step 7 and reset 

burner controls to operate automatically at this higher stack gas oxygen level. This 
7/95 ATTACHMENT 1 RULE 74.15.1: 10

margin above the minimum oxygen level accounts for fuel variations, variations in 

atmospheric conditions, load changes, and nonrepeatability or play in automatic controls.

9. If the load of the combustion unit varies significantly during normal operation, repeat 

Steps 1-8 for firing rates that represent the upper and lower limits of the range of the load. 

Because control adjustments at one firing rate may affect conditions at other firing rates, 

it may not be possible to establish the optimum excess oxygen level at all firing rates. If 

this is the case, choose the burner control settings that give best performance over the 

range of firing rates. If one firing rate predominates, settings should optimize conditions 

at that rate.

10. Verify that the new settings can accommodate the sudden changes that may occur in daily 

operation without adverse effects. Do this by increasing and decreasing load rapidly 

while observing the flame and stack. If any of the conditions in Step 5 result, reset the 

combustion controls to provide a slightly higher level of excess oxygen at the affect firing 

rates. Next, verify these new settings in a similar fashion. Then make sure that the final 

control settings are recorded at steady-state operating conditions for future reference.
7/95 ATTACHMENT 1 RULE 74.15.1: 11

Figure 1

Oxygen/CO Characteristic Curve

Figure 2

Oxygen/Smoke Characteristic Curve
7/95 ATTACHMENT 2 RULE 74.15.1: 12

ATTACHMENT 2

Equipment Tuning Procedure

for Natural Draft-Fired Equipment

Nothing in this Equipment Tuning Procedure shall be construed to require any act or omission 

that would result in unsafe conditions or would be in violation of any regulation or requirement 

established by Factory Mutual, Industrial Risk Insurers, National Fire Prevention Association, the 

California Department of Industrial Relations (Occupational Safety and Health Division). the 

Federal Occupational Safety and Health Administration, or other relevant regulations and 

requirements. Steps in the Procedure not applicable to specific units may be omitted.

1. Preliminary Analysis

a. Verify that the boiler, steam generator, or process heater (unit) is operating at the 

lowest pressure or temperature that will satisfy load demand. This pressure or 

temperature will be used as a basis for comparative combustion analysis before 

and after tune-up.

b. Verify that the unit operates for the minimum number of hours and days necessary 

to perform the work required.

c. Verify that the size of air supply openings is in compliance with applicable codes 

and regulations. Air supply openings must be fully open when the burner is firing 

and air flow must be unrestricted.

d. Verify that the vent is in good condition, properly sized and free from obstruction.

e. Perform a combustion analysis (CO, O2, etc.) at both high and low fire, if 

possible. Record all data, as well as the following: 

(1) Inlet fuel pressure at burner at high and low firing rates.

(2) Pressure above draft hood or barometric damper at high, medium and low 

firing rates.

(3) Steam pressure, water temperature, or process fluid pressure or 

temperature entering and leaving the unit.

(4) Inlet fuel use rate if meter is available.

2. Checks & Corrections

a. Clean all dirty burners or burner orifices. Verify that fuel filters and moisture 

traps are in place, clean, and operating properly. Confirm proper location and 
7/95 ATTACHMENT 2 RULE 74.15.1: 13

orientation of burner diffuser spuds, gas canes, etc. Replace or repair damaged or 

missing burner parts.

b. Remove external and internal sediment and scale from heating surfaces.

c. Verify that the necessary water or process fluid treatment is being used. Confirm 

flushing and/or blowdown schedule.

d. Repair all leaks. In addition to the high-pressure lines, check the blow-off, drain, 

safety valve, bypass lines and, if used, the feed pump.

3. Safety Checks

a. Test primary and secondary low water level controls.

b. Check operating and limit pressure and temperature controls.

c. Check pilot safety shut off operation.

d. Check safety valve pressure setting and verify that the setting is consistent with 

unit load requirements.

e. Check limit safety control and spill switch.

4. Adjustments

Perform the following checks and adjustments on a warm unit at high fire:

a. Adjust unit to fire at the maximum inlet fuel use rate: record fuel manifold 

pressure.

b. Adjust draft and/or fuel pressure to obtain acceptable, clean combustion at both 

high, medium and low firing rates. The carbon monoxide (CO) value should not 

exceed 400 parts per million (PPM) at 3% O2.

Verify that unit light-offs are smooth and safe. Perform a reduced fuel pressure 

test at both high and low firing rates in accordance with the manufacturers 

instructions.

c. Check and adjust the modulation controller. Verify proper, efficient and clean 

combustion through the range of firing rates.

When optimum performance has been achieved, record all data.

5. Final Test
7/95 ATTACHMENT 2 RULE 74.15.1: 14

Perform a final combustion analysis on the warm unit at high, medium and low firing 

rates, if possible. Record data obtained from combustion analysis, as well as the 

following: 

a. Inlet fuel pressure at burner at high and low firing rates.

b. Pressure above draft hood or barometric damper at high, medium and low firing 

rates.

c. Steam pressure, water temperature, or process fluid pressure or temperature 

entering and leaving the unit.

d. Inlet fuel use rate if meter is available.