Video Companion: How to Use a Combustion Analyzer

Combustion analysis is a critical process for HVAC professionals to ensure the safe, efficient, and reliable operation of heating appliances. This comprehensive guide provides in-depth technical insights and practical instructions on the proper use of a combustion analyzer, covering essential measurements, operational procedures, and interpretation of results.

Understanding the Combustion Analyzer

A combustion analyzer is an indispensable diagnostic tool that measures and calculates various parameters of flue gas, providing data that is otherwise undetectable by human senses. These devices are crucial for optimizing appliance performance, identifying potential hazards, and ensuring compliance with safety standards. For a wide range of diagnostic tools, visit our HVAC Tools category.

What a Combustion Analyzer Measures and Calculates

Modern combustion analyzers typically feature sensors for key gases and environmental factors, while also performing calculations to derive additional critical values. [1] [2]

Measurement/Calculation	Description
Oxygen (O2)	Directly measured, indicates excess air. Typical readings are 5-12%. 0% or 20% indicate poor combustion. [2]
Carbon Monoxide (CO)	Directly measured, indicates incomplete combustion. Typical readings are 0-80 ppm. Levels >200 ppm are concerning. [2]
Carbon Dioxide (CO2)	Calculated from O2, indicates combustion efficiency. Typical readings are 5-10%. [2]
Stack Temperature	Directly measured, temperature of flue gas. Indicates heat loss. Typical for 90% AFUE is 80-120°F, for 80% AFUE up to 400°F. [2]
Excess Air (EA)	Calculated, indicates air beyond what\'s needed for complete combustion. Typical readings are 10-150%. [2]
CO Air-Free (COAF)	Calculated, normalizes CO readings by removing the effect of dilution air, providing a more accurate assessment of combustion. Always higher than \'as-measured\' CO. [1] [2]
Draft Pressure	Measured by some analyzers, indicates negative pressure in the flue, crucial for natural draft appliances. [1]

Performing a Combustion Analysis: Step-by-Step Guide

Accurate combustion analysis requires adherence to a systematic procedure. This ensures reliable data collection and prevents damage to the analyzer or inaccurate readings. [1]

Preparation and Setup

1. Zeroing the Analyzer: Start the combustion analyzer in the cleanest air available, away from any combustion exhaust sources. This allows the sensors to zero themselves accurately. [1]
2. Appliance Identification: Identify the type of appliance being tested (e.g., furnace, boiler, water heater). This helps in understanding expected values and appropriate test points. For various HVAC systems and components, refer to our HVAC Systems & Components category.
3. Sample Location: Determine the correct sample location in the flue, which should be after the heat exchanger but before any dilution air is added. Incorrect placement can lead to inaccurate readings. [1]

Testing Procedure

1. Insert Probe: Carefully insert the sample probe into the designated sample location. [1]
2. Start Pump and Appliance: Start the analyzer\'s pump, then initiate the appliance\'s burner. [1]
3. Monitor Readings: Continuously observe and record the displayed values throughout the startup, run, and shutdown cycles of the appliance. [1]

Post-Analysis

1. Remove Probe: After the burner(s) are completely shut down, remove the analyzer probe from the sample location. [1]
2. Purge Sensors: Allow the analyzer\'s pump to continue running with the probe in a clean environment until CO readings return to near-zero (0-1 ppm). This purges residual combustion gases, extending sensor life. [1]

Interpreting Results and Acceptable Levels

Understanding the measured and calculated values is crucial for diagnosing appliance performance and safety. Elevated CO levels are a primary concern, indicating incomplete combustion and potential safety risks. [1]

Carbon Monoxide (CO) Thresholds

Industry standards and manufacturer specifications provide acceptable CO levels. Always prioritize manufacturer recommendations. If unavailable, refer to industry limits for safety. [1]

Appliance Type	Threshold Limit
Central Furnace (all categories)	400 ppm air free
Boiler	400 ppm air free
Floor Furnace	400 ppm air free
Gravity Furnace	400 ppm air free
Wall Furnace (BIV)	200 ppm air free
Wall Furnace (Direct Vent)	400 ppm air free
Vented Room Heater	200 ppm air free
Unvented Room Heater	200 ppm air free
Water Heater	200 ppm air free
Oven/Broiler	225 ppm as measured
Clothes Dryer	400 ppm air free
Refrigerator	25 ppm as measured
Gas Log (gas fireplace)	25 ppm as measured in vent
Gas Log (installed in wood burning fireplace)	400 ppm air free in firebox

Source: ANSI/BPI-1200-S-2017, Section 7.9.7, Table 1 [1]

Oxygen (O2) Levels

For most heating equipment, acceptable oxygen levels in undiluted flue gas range from 6-9%, unless otherwise specified by the manufacturer. [1]

Maintenance and Safety Considerations

Regular maintenance of your combustion analyzer and adherence to safety protocols are paramount for accurate operation and technician well-being. For information on various heating and cooling equipment, explore our Air Conditioners & Heat Pumps category.

Analyzer Maintenance

• Daily: Empty water trap, inspect/replace particulate filters, protect from freezing, purge sensors after each test, check hoses/gaskets. [1]
• Annual: Calibrate at an authorized service center, detailed physical inspection, regular sensor replacement (electrochemical sensors degrade over time). [1]

Safety Precautions

Technicians must be aware of hazards such as flue gas spillage, hot surfaces, and condensate leakage. Appropriate Personal Protective Equipment (PPE) like gloves, safety glasses, and long sleeves are recommended. [1]

Frequently Asked Questions (FAQ)

Q1: Why is it important to zero the combustion analyzer in fresh air?

A1: Zeroing the analyzer in fresh, clean air ensures that the sensors establish an accurate baseline. If zeroed in contaminated air, subsequent readings will be skewed, leading to incorrect diagnostic conclusions. [1]

Q2: What is the significance of CO Air-Free readings?

A2: CO Air-Free (COAF) normalizes the carbon monoxide reading by removing the diluting effect of excess air. This provides a more consistent and accurate measure of CO produced by the combustion process, making it easier to compare readings and diagnose issues regardless of excess air levels. [1] [2]

Q3: Can a combustion analyzer definitively identify a cracked heat exchanger?

A3: A combustion analyzer can indicate a potential issue with a heat exchanger if the crack affects the combustion process, leading to abnormal flue gas readings. However, it is not a definitive tool for crack detection. Visual inspections and other specialized methods are often required for conclusive diagnosis. [1]

Q4: How often should a combustion analyzer be calibrated?

A4: Combustion analyzers should be calibrated annually by an authorized service center or the manufacturer. Regular calibration ensures the accuracy and reliability of the instrument\'s measurements, which is critical for safety and efficiency assessments. [1]

Q5: What should I do if the CO level on the analyzer approaches its upper measurement limit?

A5: If CO levels rapidly approach or exceed the analyzer\'s upper limit, immediately disconnect the probe or remove it from the flue to introduce fresh air to the sensors. Prolonged exposure to high CO concentrations can cause permanent damage to the electrochemical sensors within the analyzer. [1]