If you subscribe to a Google News Alert for carbon monoxide (CO), you’ll see most stories mention a “CO leak” as the cause of CO poisoning. These stories imply there are always dangerous CO levels in the venting system. They assume it’s only when these gases “leak” out that a poisoning occurs. Most of the public and many in our industry have bought into this myth as though it’s normal and acceptable. However, it couldn’t be further from the truth.
Maintaining acceptable CO levels in flue gases is necessary, but our industry rarely measures or enforces them. When did a code official last ask you to measure a system you installed for flue gas CO levels? A tougher question might be, when did you last measure flue gas CO levels in a system you installed? Let’s examine what’s happening when you hear about a “CO leak” and how to protect your customers from the danger.
Defining a CO Leak
The phrase “CO leak” is a misinterpretation of what’s happening during equipment operation. CO spills, it doesn’t leak, and it’s never acceptable when a CO spill happens. In fact, spillage indicates improper flue gas venting and unsafe equipment operation.
Consider this: Since CO spills, why hasn’t there been a demand to stop them, put safety measures in place for prevention, and improve awareness? Instead, we wait for the boogeyman to strike and tolerate situations that could put you and your customers in unsafe conditions. Why do we continue to play Russian roulette with CO safety?
How Does CO Spill?
There are multiple locations where flue gases spill from vented equipment. These include drafthoods on natural draft equipment, burner inlets, chimneys, and building openings. It’s important to note that flue gases and room air can move into or out of these openings. They act as two-way streets for flow.
Draft pressure is the force that determines the direction of flow. Uncontrolled draft can contribute to CO spilling from a venting system and connected equipment. Low or excessive draft creates competition for airflow that causes carbon dioxide (CO2) to build up in the burner compartment. CO2 is a heavier gas and one of the main byproducts of combustion. It starves equipment for combustion air as it builds up internally.
This is often the cause of what we often misinterpret as a CO leak. The equipment operates improperly when this condition exists, and it remains hidden if you test for it using current industry protocols. The two most common of these protocols are:
· A single CO test in the equipment’s flue gas after 10 minutes of operation
· Using chemical smoke at the base of a drafthood.
Discovering CO Spillage
There are often visual signs indicating spillage is happening. Look for the following clues as a starting place.
1. Melted water pipe grommets or electrical wiring
2. Rusting around drafthoods
3. Rust in the burner compartment
4. Discoloration of the burner compartment.
The only way to verify if spillage happens is to take multiple CO measurements in the flue gas while the equipment operates. Stable CO readings below 100 parts per million (ppm) indicate the equipment is venting correctly while rising CO readings during the run cycle indicate flue gas is spilling.
In the example above, the CO measurement remains stable as the equipment continues to operate over 12 minutes. The CO readings stay below 100 ppm and are stable. In the above example, the equipment is venting correctly.
In this example, the CO measurement continues to climb and doesn’t stabilize. This is an appliance that is spilling flue gas and is unsafe to operate. CO levels will continue to climb until the equipment cycles off. If it operates long enough, CO levels will rise so high that a combustion analyzer won’t be able to display the reading. A traditional test will miss this safety issue.
The Solution
Our industry can address the cause of spillage with proper testing, equipment monitoring, and by using fewer assumptions. A properly designed and operating system shouldn’t spill CO. If it does, the safeties should turn the equipment off so it doesn’t endanger anyone.
If you focus only on the equipment to solve CO spillage, you may be looking in the wrong location. Many causes of CO spillage have nothing to do with the equipment. Instead, they have everything to do with the equipment’s environment. External influences such as exhaust fans, duct leakage, airflow imbalances, and building pressures often interfere with proper draft and cause spillage through an interaction known as back-drafting. A firm understanding of building science and diagnostics is priceless when diagnosing back-drafting issues.
Also, offer low-level CO monitors to your customers instead of over-the-counter CO alarms. Many believe store-bought CO alarms provide the same protection as low-level CO monitors. They don’t. Your customers deserve a device that prevents exposure to excessive CO levels before they alarm. Why not equip them with a safeguard that lets them know they are at risk before harmful levels build up?
Unfortunately, some will continue to use the CO leak as an excuse for their lack of understanding and troubleshooting skills. Don’t be that person. Instead, move past the excuses and find out the actual reasons. We can improve our industry and our customers’ safety with proven solutions that prevent CO poisonings from ever being a news story again.
David Richardson serves the HVAC industry as Vice President of Training for the National Comfort Institute, Inc. (NCI). NCI specializes in training focusing on improving, measuring, and verifying HVAC and building performance.
If you’re an HVAC contractor or technician interested in learning more about how to start combustion testing, contact David at ncilink.com/ContactMe. NCI’s website www.nationalcomfortinstitute.com is full of free information to help you improve your professionalism and strengthen your company.
Photo Captions
Photo 1: Would a rip in the flue allow CO to “leak” into a building? What if the flue gases never reached this opening or measured 10 ppm on a combustion analyzer?