Key Takeaways
- CO Detection is Critical: Carbon monoxide is colorless, odorless, and can be lethal at just 70 ppm – every HVAC tech needs proper testing equipment
- Test Every Service Call: Always check ambient air, mechanical room, appliance area, supply air, and flue gas – not just when you suspect a problem
- Know Your Action Limits: Under 50 ppm is normal, 200 ppm requires adjustment, and 400+ ppm means immediate shutdown
- Document Everything: Proper record-keeping protects you legally and ensures customer safety – calibrate equipment annually
The Truth About CO
You do not need massive amounts of CO to create a dangerous situation. While air normally contains about 200,000 parts per million (ppm) of oxygen, just 70 ppm of CO can start causing problems for healthy adults. At 400 ppm, you are looking at potential unconsciousness and death within a couple of hours of exposure.
Carbon monoxide (CO) is a colorless, odorless, tasteless, and highly toxic gas that is produced during incomplete combustion. As professional HVAC technicians, we need to understand that even at low concentrations, CO binds to hemoglobin in the blood with an affinity 200-250 times greater than oxygen, preventing oxygen from being transported throughout the body.
Here is a quick breakdown of CO exposure effects:
- 9 ppm: Maximum allowable concentration for short-term exposure in living environments (ASHRAE standard)
- 35 ppm: Maximum allowable concentration for continuous exposure in any 8-hour period (US federal law)
- 200 ppm: Maximum allowable concentration at any time according to OSHA (can cause headaches, fatigue, and nausea after 2-3 hours)
- 800 ppm: Nausea and convulsions within 45 minutes and death within 2-3 hours
- 3,200 ppm: Headaches and nausea within 5-10 minutes and death within 30 minutes
Why Should You Care?
Every time you work on a furnace, boiler, or water heater, you are dealing with equipment that could potentially produce CO. But unlike smoke, you cannot see it, smell it, or taste it. That is why we call it the “silent killer.” Without proper testing, you might walk away from a job thinking everything is fine, while leaving behind a potentially lethal situation.
As professional HVAC technicians, we are on the front lines of CO safety. The stark reality is that improper combustion analysis or overlooked maintenance can lead to serious health risks or even fatalities. When a crack develops in a heat exchanger, when venting becomes compromised, or when fuel/air mixtures are incorrect, deadly CO can leak into living spaces. This is especially critical during seasonal maintenance scheduling when heating systems are being prepared for winter operation.
Tools of the Trade
This is where having the right equipment becomes crucial. Seitron’s lineup, particularly the Novo analyzer, is designed specifically for techs like us who need accurate, reliable readings.
Here is what you should be looking for in your CO testing equipment:
1. Ambient CO Detection
- Built-in ambient monitor for immediate safety checks
- Alerts you to dangerous conditions before you even start working
- Should be carried and used on every service call, not just heating system repairs
2. Combustion Analysis Capabilities
- Measures O2, CO2, and CO simultaneously
- Helps you dial in that perfect combustion setup
- Calculates combustion efficiency to optimize system performance
3. Data Recording
- Keeps track of your readings for documentation
- Provides evidence of your proper testing procedures
- Covers you legally if questions come up later
Real-World Testing Protocol
Before starting any testing procedure, always zero your CO instrument in fresh air. This establishes an accurate baseline for your measurements. Then, follow these testing points:
1. Ambient Air Testing
Walk into the house with your CO meter on and sampling. Any measurement above zero is not normal, as CO is only present as a byproduct of combustion. In homes where people smoke or burn scented candles, readings between 2-6 ppm are common. Anything above 6 ppm should be investigated.
2. Water Heaters
- Check combustion readings (O2, CO2, CO)
- Verify stack temperature
- Measure draft
3. Furnaces (80%)
- Test gas pressure
- Check limit and pressure switches
- Verify proper combustion parameters
- Monitor static duct pressure
- Check mechanical room CO levels
- Test appliance vestibule and burner area (readings should match ambient air)
- Test supply air stream in the plenum (any increase indicates potential heat exchanger issues)
4. High-Efficiency Units (90%+)
- All the above, plus
- Verify condensate drainage
- Check inducer operation
- Inspect venting system for proper installation and operation
The Numbers That Matter
Here is your quick reference guide for flue gas measurements:
- Under 50 ppm: Normal for most modern gas appliances
- Up to 175 ppm: Acceptable for some high-efficiency boilers
- 200 ppm: Your absolute maximum before requiring adjustment
- 400 ppm: Red tag territory – shut it down
For different heating systems, here are the typical acceptable combustion results (always follow manufacturer’s specifications):
Gas Fired Power Burners
| Parameter | Acceptable Range |
|---|---|
| Oxygen (O2) | 3-6% |
| Carbon Monoxide (CO) | < 100 ppm |
| Carbon Dioxide (CO2) | 8.0-11.0% |
| Stack Temperature | 275-500 degrees F |
| Stack Draft | -0.02 to -0.04 inWC |
High-Efficiency Gas Fired 90+ Power Burners
| Parameter | Acceptable Range |
|---|---|
| Oxygen (O2) | 5-7% |
| Carbon Monoxide (CO) | < 100 ppm |
| Carbon Dioxide (CO2) | 7.0-9.0% |
| Stack Temperature | Less than 125 degrees F |
| Stack Draft | +0.02 to +0.08 inWC |
Pro Tips from the Field
- Always calibrate your analyzer annually – using uncalibrated equipment is asking for trouble
- Test on every call, not just when you think there might be a problem
- Look for trends over time – rising CO levels can indicate developing problems
- Know that flue gas readings and ambient readings are completely different measurements
- Pay attention to the relationship between O2, CO2, and CO readings during combustion analysis
- Remember that excess air impacts combustion efficiency and emissions (too little air = increased CO production)
- Document everything – it is not just good practice, it is legal protection
Understanding Combustion Analysis
For novice technicians, it is important to understand that combustion analysis is more than just checking CO levels. It is a comprehensive evaluation of how efficiently and safely a combustion system operates. During combustion analysis, we measure:
- O2 (Oxygen) – Tells us about excess air conditions
- CO2 (Carbon Dioxide) – Indicates combustion completeness
- CO (Carbon Monoxide) – Safety indicator and efficiency measure
- Stack Temperature – Shows heat transfer efficiency
- Draft Pressure – Ensures proper venting
Remember the basic concept: combustion requires the right balance of fuel, oxygen, and heat. When these elements are in proper proportion, combustion is efficient and clean. When this balance is disrupted, we get incomplete combustion and that leads to CO production.
As a technician working with combustion appliances, you are responsible for ensuring this balance is optimized for both efficiency and safety. Think of combustion analysis as your diagnostic tool for the heart of the heating system. This becomes especially important when working with complex BMS network architecture in commercial buildings where multiple combustion appliances may be monitored remotely.
Safety First
Remember, if you ever find CO levels above 400 ppm in the flue gas, or any CO in the living space:
- Shut down the equipment immediately
- Ventilate the area
- Notify the customer of the hazard
- Document your findings
- Do not restart until the problem is fixed
Your personal safety matters too! Always ensure your own safety when performing any HVAC work. Carry a personal CO monitor whenever working around combustion equipment. ASHRAE recommends a maximum exposure limit of 9 ppm in living environments, and this applies to you as well while you are working.
Taking it to the Next Level
Want to really step up your game? Seitron offers complete system solutions that can include:
- Portable analyzers for service calls
- Fixed monitors for ongoing protection
- Data logging capabilities for building management systems
Professional combustion analysis goes beyond basic safety checks it can help you optimize system efficiency, reduce fuel consumption, and extend equipment life. By understanding and correctly interpreting combustion readings, you provide greater value to your customers while ensuring their safety.
As you gain experience with combustion analysis, you will develop an intuitive understanding of the relationships between different readings and what they tell you about a system’s operation. This expertise will set you apart as a technician who truly understands the science behind heating systems, especially when preparing for commercial HVAC maintenance season.
The Bottom Line
As HVAC techs, we are on the front lines of keeping people safe from CO poisoning. Every service call is an opportunity to prevent a tragedy. Take the time to do proper testing, invest in quality equipment, and never cut corners when it comes to combustion safety.
Remember: Your customers trust you with their lives, even if they do not realize it. Make sure you are worthy of that trust by mastering CO testing and safety protocols.
Need more guidance on combustion analysis and other HVAC topics? Check out our latest blog posts and consider subscribing to the HVAC Know It All Podcast for ongoing professional development.
