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Carbon Monoxide Alarm vs Low Level CO Monitor

Today most people are aware of the invisible, odorless, poisonous gas of Carbon Monoxide or CO for short. Now we know that even low levels of CO can have long term health effects depending on exposure time, the health and age of the exposed person. Carbon Monoxide binds with the hemoglobin in the blood 300 times more than Oxygen. It is believed that Florence Nightingale's ailments may have stemmed from CO poisoning from her coal heater in Russia. Some haunted houses were actually from CO poisoning and its effects on the brain. It turns out the HVAC professional can be more effective than the exorcist! While the flu and cold is more prevalent in the winter, sometimes it is actually CO poisoning with similar symptoms. We need to be more aware!

What are Safe Levels For Carbon Monoxide?

What are safe levels for CO? It depends on who you ask, but I think we can all agree the less poisonous gas we breathe the better. It will be measured in How Many Parts of CO Per Million Parts of Air. This is referred to as PPM (Parts Per Million). The World Health Organization says 9-10 PPM for no more than 8 hours, 23-35 PPM no more than 1 hour and 90-100 PPM no more than 15 minutes. The National Institute for Occupational Safety and Health recommends no higher than 35 PPM over an 8 hour period. OSHA on the other hand set a limit of 50 PPM over an 8 hour period. These organizations may set limits on the CO PPM amount while sleeping, while active, and while working and you can read up on their recommended limits directly from them. However, for the sake of this article, we are just focusing on the fact that we need a method to accurately measure and notify us if CO is present.

Carbon Monoxide Alarm

So what does a CO Alarm sound off at? In the USA, CO alarms are UL rated (UL 2034/CSA 6.19) and will usually NOT sound off below 30 PPM! They may have a mandatory response of 70 PPM within 60-240 minutes, 150PPM within 10-50 Minutes, and 400 PPM within 4-15 minutes. By the time a CO alarm sounds off at those very high levels, it is an emergency! The first CO alarms where first introduced in 1992. In 1994 a strong weather inversion occurred in Chicago that trapped CO and other air pollutants at ground level and the Fire department responded to over 2000 emergency calls with 30 people in the ER. We knew a lot less about CO back then, but we knew the fire department was overrun with more calls than they could handle. This lead to the regulations of higher limits before an alarm would sound as an emergency.

Carbon Monoxide Monitor

What is a better solution than a high level alarm? Installing a low level CO monitor is a solution that will notify the occupants of the risk well before it becomes an emergency. By law, this cannot be called an alarm, thus the name "low level CO monitor". While different manufacturers have varying levels of notification, ideally it will have some warning at 10 PPM. This lower level warning will allow time for a professional to come and find the cause. While people often blame the furnace, it can also be a water heater, fireplace, unvented stove, oven, or even an attached garage. Yes, even an all electric house can suffer from an unhealthy level of CO just by backing a car in or out of the garage. It is important for the source to be identified and corrected although sometimes the source can be misleading such as a golf cart charger.

I recommend anyone in the trades or even on a camping trip to also carry a personal low level CO monitor. This will notify the worker when they are entering a potentially hazardous situation. One time mine went off in the summer when I was brazing an evaporator in a walk in cooler. Someone had closed the door while I was working, but my personal low level monitor alerted me to the hazard. When I started in the trade, wearing PPE such as gloves and safety glasses where not as common but now considered common sense. I hope having low level CO monitors in homes, businesses and on-person becomes just as common.

To learn more, I recommend reading "Carbon monoxide: a clear and present danger" by Bob Dwyer

HVAC E learn network has an online course for CO and combustion analysis

You can find a variety of low level CO monitors and alarms at True Tech Tools! Use our promo code: acservicetech, for 8% off any order!

EPA Gov Link

Published: 11/29/2023 Author: Ty Branaman

About the Author: Ty is a nationally renowned HVACR Teacher that has over 20 years experience teaching high school, post secondary, and in-field technician students. Ty does on-site training events and ride-along training. Ty also makes instructional videos to share his knowledge. Ty can be reached at and his video library is available here:



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