8.6 Gas Burner Safety & Efficiency Service
Gas burners should be inspected and maintained during a service call. These following specifications apply to gas furnaces, boilers, water heaters, and space heaters.
8.6.1 Combustion Efficiency Test for Furnaces
Perform the following procedures at steady-state to verify a furnace’s acceptable operation.
Perform combustion testing with an electronic flue-gas analyzer that documents accurate combustion air temperature so that net stack temperature is calculated correctly. The testing location should be as close to the flue outlet of the unit as possible to reduce false O2 numbers and to obtain accurate flue gas temperatures.
• Measure temperature rise (supply minus return temperatures). Temperature rise should be within the manufacturer’s specifications for the furnace.
• Recommended flue-gas temperatures depend on the type of furnace and are listed in the table titled, “Combustion Standards for Gas Furnaces and Boilers” on page 275.
• As appropriate, adjust gas pressure so that temperature rise and flue-gas temperature meet manufacturer's specifications and per guidance from the National Fuel Gas Code (NFPA 54).
8.6.2 Inspecting Gas Combustion Equipment
Inspect all gas-fired furnaces, boilers, water heaters, and space heaters according to these steps.
✓ Look for soot, melted wire insulation, and rust in the burner and manifold inside and outside the burner compartment. These signs indicate flame roll-out, combustion gas spillage, CO, and incomplete combustion.
✓ Inspect the burners for dust, debris, misalignment, flame-impingement, and other flame-interference problems. Clean, vacuum, and adjust as needed.
✓ Inspect the heat exchanger for cracks, holes, or leaks.
✓ Verify that furnaces and boilers have dedicated circuits with safety shutoffs nearby. Verify that all 120-volt wiring connections are enclosed in covered electrical boxes.
✓ Verify that pilot is burning (if equipped) and that main burner ignition is satisfactory.
✓ Check venting system for proper diameter and pitch. See page 306.
✓ Check venting system for obstructions, blockages, or leaks.
✓ Observe flame characteristics. Flames should be blue and well shaped. If flames are white or yellow, the burner may suffer from faulty combustion.
See “HVAC-System Commissioning” on page 252. See “HVAC-System Education” on page 253.
The goal of these measures is to minimize carbon monoxide (CO), stabilize flame, and verify the operation of safety controls.
✓ Do an electronic combustion analysis and note the oxygen, CO, and flue-gas temperature.
✓ Test for spillage and measure draft. Take action to improve the draft if it is inadequate because of improper venting, obstructed chimney, leaky chimney, or depressurization. See page 263.
✓ If you measure CO and the measured oxygen level is low, open a window while observing CO level on the meter to see if CO is reduced by increasing the available combustion air through the open window. See “Worst-Case CAZ Depressurization Test” on page 258.
✓ Adjust gas input if combustion testing indicates over-firing or under-firing.
✓ For programmable thermostats, read the manufacturer’s instructions about how to control cycle length. These instructions may be printed inside the thermostat.
Burner Cleaning
Clean and adjust the burner if any of these conditions exists.
• CO is greater than 100 ppm as measured or 200 ppm air-free measurement for space heaters and water heaters; or 200 ppm as measured or 400 air-free for furnaces or boilers.
• You see indicators of soot or flame roll-out.
• Burners are visibly dirty.
• The appliance spills for more than two minutes or measured draft is inadequate. See page 306.
• The appliance hasn’t been serviced for two years or more.
Maintenance and Cleaning
Gas-burner and gas-venting maintenance should include the following measures.
✓ Remove causes of CO and soot, such as over-firing, closed primary air intake, flame impingement, and lack of combustion air.
✓ Remove dirt, rust, and other debris that may be interfering with the burners. Clean the heat exchanger if there are signs of soot around the burner compartment.
✓ Seal leaks in vent connectors and chimneys.