graphic for Carbon Monoxide column by David Richardson

Carbon Monoxide: Carbon Monoxide and the Flu

December 17, 2018

By David Richardson

David Richardson, NCI Trainer

The day before writing this I was in the doctor’s office for my yearly physical. One of the first questions the doctor asked me was “Have you had a flu shot this year?” He reminded me that it’s the time of year when many of us get “flu-like” symptoms that include: a runny nose, stuffy head, muscle aches, and fever.

Since I’m a CO (carbon monoxide) guy, my thoughts naturally drift to wondering how many people are also experiencing identical symptoms that are related to CO poisoning. Every symptom I listed is also tied to low-level CO poisoning.

How would you know if you are being poisoned or just have a bad case of the flu? Let’s look at some steps you can take to protect yourself, your loved ones, and customers if you notice these symptoms

Measure the Air You Breathe

It’s easy to assume the air we breathe is safe. After the first day of an NCI CO and Combustion class, the importance for measuring ambient CO is clear. It’s common for HVAC professionals we train to make surprising discoveries once they begin to measure.

In one instance a technician’s personal low-level CO monitor alerted him when he walked into a customer’s home. The monitor displayed 35 ppm (parts per million). This made him aware he was entering a potentially dangerous situation.

As he questioned the customer and shared his findings with them, they told him they had been ill, and it wouldn’t go away. The technician realized the family was being poisoned by low level CO. How many HVAC professionals would have walked past this exact situation? If you don’t measure, you’re just guessing.

Be Aware of Symptoms

Low-level CO poisoning symptoms are extensive. If you or someone else suffers from flu-like symptoms such as a stuffy head, sore throat, fever, fatigue, vomiting, chest pain, and so on, it may be related to the “flue,” not the “flu.”

One item I recommend students in our classes look for is whether symptoms move. For example, do the symptoms only occur at one location, such as at work or home? When you move away from the location where you notice the symptoms, do you feel better?

This simple awareness can help you determine if a problem is environmental, or if you’re truly sick. If the problem is environmental, you’ll typically feel better once you leave the contaminated area. If you have an illness, you’ll feel bad wherever you are.

Test Equipment for CO

If you measure ambient CO, you’ll need to continue testing to uncover what is creating it. Don’t guess the heat exchanger has a crack in it. Equipment must be measured using a combustion analyzer, draft gauge, and proper test procedures.

Obtain flue gas measurements from the smallest vented appliance first. If you measure CO readings in the flue greater than 400 ppm or CO readings continue to rise during the run cycle, the equipment is unsafe and should be turned off. Once you determine safe operation, move to the next largest vented appliance and repeat the steps.

After testing all vented equipment, move to unvented appliances such as a gas range or unvented gas logs. CO readings from these appliances should be 50 ppm or less since they dump flue gases directly into the building. If you encounter unvented appliances, be sure to recommend appropriate exhaust ventilation.

Understand Store-Bought CO Alarms

Many consumers and contractors alike believe store-bought CO alarms provide low-level CO poisoning protection. Don’t make this mistake – they do have limitations. These alarms are designed to protect middle-aged healthy adults from life threatening CO levels. Store-bought alarms are rated by UL standard 2034 that states these alarms can be exposed to the following CO amounts:

  • 70 ppm +/- 5 ppm for 60 to 240 minutes
  • 150 ppm +/- 5 ppm for 10 to 50 minutes
  • 400 ppm +/- 10 ppm for 4 to 15 minutes

False alarm (No alarm during these levels) levels are: 30 ppm +/- 3 ppm for 30 days and 70 ppm +/- 5 pm for 60 minutes.

As you can see these devices aren’t designed to alarm at low CO levels. Unless you’re equipped with a low-level monitor, you won’t know whether CO poisoning is contributing to your flu symptoms or not.

About the Author

David Richardson serves the HVAC industry as a curriculum developer and trainer at the National Comfort Institute, Inc. (NCI). NCI specializes in training focused on improving, measuring, and verifying HVAC and Building Performance.

If you’re an HVAC contractor or technician interested in learning more about adding combustion testing to your services, contact David at or call him at 800-633-7058. NCI’s website is full of free technical articles and downloads to help you improve your professionalism and strengthen your company.