graphic for Carbon Monoxide column by David Richardson

Carbon Monoxide: Three Sherlock Holmes Quotes About CO Testing

February 19, 2019

By David Richardson

David Richardson, NCI Trainer

One of my favorite fictional characters growing up was Sherlock Holmes. Holmes was an extraordinary detective with a gift for finding clues that others completely missed. His confidence, observational skills, and attention to detail added an extra appeal to the stories.

Little did I know Sherlock Holmes’ qualities would apply to my CO (Carbon Monoxide) testing skills years later. Holmes solved his cases based on bite-sized clues and the logical order in which events must occur. When you test for CO, you put together your diagnosis in a similar manner.

In the Sherlock Holmes stories, you’ll find some great quotes based around his style of detective work. Let’s look at three such quotes that not only give us a glimpse into this great character’s mind, but also insight to how he might have conducted CO testing.

“It is a capital mistake to theorize before one has data.”

Holmes didn’t put together the case’s conclusion before he had enough evidence to connect all the dots. He gathered clues from the murder scene and observed how they related to each other through his keen sense of observation.

If Holmes handled his investigations like so many in our industry handle CO calls, the Butler would always be the one “whodunit.” There would be no additional data gathered and the case would be closed before arriving at the crime scene.

The “Butler” in the HVAC industry is often the furnace heat exchanger. Many technicians who receive residential CO alarm calls head straight to the heat exchanger. This component is condemned and found guilty with no additional data to back up the conclusion.

Now consider what a CO call would look like if a technician handled it like Sherlock Holmes. First, adequate data would be gathered from the scene. A combustion analyzer and draft gauge are used to gather essential information and combined with proper troubleshooting skills to track down the true CO alarm cause. They have the data they need instead of theorizing first.

Once necessary information is gathered, logical conclusions are made based on clues discovered with measurements. Sometimes the measurements point to a suspect that doesn’t make sense. This leads us to our next quote.

“There is nothing more deceptive than an obvious fact.”

When you test for CO, your measurements and data may point to a suspect you originally didn’t consider. Or, it may point you to a suspect that is contrary to what you’ve learned in the past. Holmes urges us to not be deceived by obvious facts, but to let the data lead us to our conclusions.
A decade ago, while teaching a class in Dallas, Texas, we were testing in a vocational school lab. The HVAC lab was a large room at one end of the building. On the opposite side of the building was a carpentry lab. Both labs were directly connected.

The carpentry students were working on projects the day we tested equipment in the HVAC lab. They had a large 20 X 20 door opened to let some sunshine in while sanding and cutting wood.
In the HVAC lab, there were five pieces of natural draft equipment on the back wall, opposite the 20 X 20 door. When we started up the equipment, they all began to backdraft, spilling flue gases. The CO readings rose quickly and there was no flue draft pressure.

The HVAC students immediately looked for a blocked flue or an exhaust fan running in the lab. Neither suspect was found to be a contributing factor. So, why was the equipment spilling?
Remembering the wide-open 20 X 20 door, I asked the students if this could be the cause. Their immediate response was the door would allow air into the room and shouldn’t be an issue. I grinned and asked the students to watch the readings while I walked over and closed the door.
As soon as it closed, I heard “No way!” across the building. Pre-conceived notions proved to be deceptive and caused an obvious fact to be ignored. This leads me to the last quote from Sherlock Holmes.

“When you have eliminated the impossible, whatever remains, however improbable, must be the truth.”

When I shut the door, I eliminated the impossible. In the student’s minds, there was no way an open door could cause the equipment to spill. The assumption was made that air in the building and flue gases “knew” which way to travel.

On this windy day, outside air wanted to come down the flue and out the drafthoods. Air takes the path of least resistance. The open door provided that path. Once the door was closed, the flues became the least restrictive path and flue gas spillage stopped.

It seemed impossible, but the measurements and data pointed to the only remaining influence on our CO readings being the open door. Once we eliminated it as a possibility, it allowed us to continue with our diagnostics.

When testing for CO, you must keep an open mind and consider possibilities previously ignored. Don’t limit your troubleshooting skills by jumping to conclusions. Follow the example of Sherlock Holmes and create your own stories.

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 carbon monoxide 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.