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CO Safety Switch?

Zman Member Posts: 7,573
I always make sure all boiler installs include a co detector. I will install one if the property does not already have one. I think people are crazy not to, they only cost about $40.

Recently I put one on a job where a was concerned the owner might remove it (some of the smoke alarms in the building were disabled) I decided to strap it to the wall and take a picture.

It got me thinking. Why isn't the co detector an integral  part of the boiler system just as as LWCO. Does anyone know of a product that would disable  the boiler when CO is detected? I think it would need a manual reset and would ideally just have "dry" contacts.
"If you can't explain it simply, you don't understand it well enough"
Albert Einstein


  • icesailor
    icesailor Member Posts: 7,265
    CO requirements:

    In Massachusetts, any gas appliance newly installed (and that would require a permit) requires a permit for a CO detector and must be installed and in working order when the gas inspection is done. No CO installed and working, no approval.

    No exceptions.

    It must be on the floor of the equipment unless it is in a crawl space. In which case, it must be on the floor above.
  • Zman
    Zman Member Posts: 7,573
    Code here too


    It is code here also. People who will disable a smoke alarm will also disable a CO, especially if they don't have knowledge of the dangers of CO. There was an elderly woman in Denver who fired up a generator in her house for heat. The CO detector was disabled.She was killed. A case like this may be modern day "natural selection" but tragic non the less. With the advancements of modern controls why not have the system "lock out" for; high flue temps, lwco, and CO? These features could be built into the system and would virtually eliminate the dangers of CO.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Bob Harper
    Bob Harper Member Posts: 1,040
    CO switch technology

    To hardwire a UL listed CO alarm onto a combustion appliance is a little fruitless based upon current technology and the UL listings 2034 & 2075. These alarms will sound only once you already have a 10% COHb level and even then they are unreliable. We have relatively reliable temperature based spill switches when mounted where they will be most effective. However, where would you mount a CO switch on let's say your typical draft hood equipped gas boiler? The draft hood? Where? Flue gases are notorious for spilling out one side of draft hoods. What if the HX is plugged and its venting out of the base? What if the chimney draft is so excessive it creates a door curtain effect blocking venting at the draft hood? What if there is a shunt inside a forced air cabinet between the combustion chamber and the return air plenum? Where do you place it on CAT III & IV forced draft units? One at each joint in the venting? You see the dilemma?

    A better solution would be to require performance testing by technicians who are certified and trained in combustion analysis and CO. Positive pressure venting should be tested for integrity but we on the UL Standards Technical Panel cannot agree on this need, much less a standard. We still are working on the listing for polymer venting. CO switches on combustion appliances is actually a very complex issue. Meanwhile, if you want to offer real protection for your clients, install unlisted CO monitors in addition to the code required listed junk.

  • Charles Johnson
    Charles Johnson Member Posts: 24
    CO sensor in flue

    Maybe better than a CO switch somewhere would be a CO sensor in the flue. It could be programmed to shut off the boiler if the flue levels stayed above a predetermined number, such as 400 ppm, and maybe a "call for service" alarm whenever it stays above 200 ppm.

    It would have to be reliable so you didn't have to replace it every year.

    Why hasn't someone tried this? Too expensive?
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    didn't have to replace it every year.

    Do they make reliable ones in the sense that they did not require regular replacement? The cheapie ones seem to need replacement every 5 years or so. I think my (almost) $200 one needs regular replacement. The boxes last longer, but the sensors inside do not.

    From what I have read about digital combustion analyzers, their sensors need replacement every coupla years too.

    I had a friend who worked for a company that made alcohol detectors for police traffic law enforcement. There, too, the problem of regular replacement of the detection element was the major challenge.
  • Bob Harper
    Bob Harper Member Posts: 1,040
    different sensor technology

    Depending upon the sensor type and quality can vary its service life for years. Yes, 5 is the max. recommendation on UL listed alarms. The oxygen in the air degrades the sensor over time.That's why even unsold alarms have a limited shelf life. Very high levels of CO and NOx can adversely affect sensors, too.

    One thing you have to keep in mind is the time function. Are you going to send the calvalry for a whiff of CO? That's specifically why they dummied listed alarms down to reduce false positives and the number of alerts. They'd rather not come out unless you're almost dead Doesn't respond to chronic low levels.

    If the sensor got covered with soot, it would nullify it. The face of the sensor would have to be not only super corrosion resistant but meet the rating of the chimney/ vent and not cause turbulence or reduce the flue capacity. It would have to be written into the listing standard such as ANSI Z21.47 and listed as part of the entire appliance. A lot of problems doing this.
This discussion has been closed.