This little thing may have saved my life today (CO).

What caused the problem?

After a huge scare where I ended up in the ER, I carry one into every job. Glad you posted this yourself and not someone else posting a link about your tragic story online

Glad to hear it worked and no one got hurt!

Funny how the world tells you things, I read this post yesterday morning, and then yesterday afternoon I suspect I may have been exposed. Ordering one today, not taking the chance again.

Customer recently bought the house, complains the furnace turns on and off all time. Found the dip switches on the control board set for 2 stage heat, but no fan speed attached to the lo heat terminal on the board. so....ignition sequence was fine, but then the fan failed to come on. burner would continue until high limit tripped, then burner would shut off and high heat fan stage would come one. after figuring out the problem, I switched the furnace back to single stage heat, and watched the burner fire, and the main blower come on. This caused a huge change in the burnerw flame (pulling out of heat exchanger, going crazy) . Turned it off immeadiately, thought to myself your dumb, had the bottom cabinet door off when the fan kicked on of course its going to affect the burners. closed it up re started the furnace, and nope, still does it, combustion analyzer showed CO of over 1500 ppm in exhaust once the blower kicks on, around 150 with the blower off. heat exchanger is cracked. most likely caused by the way it has been operating for three years since it was installed. The only reason this hasn't hurt or killed anyone is becuase the burner has never been running with the main blower.

I shut the thing down and it will be replaced.

I share this because during testing, my combustion analyzer was showing 0 ppm CO if the probe was in the ambient room, or the supply plenum. however after being down there and lighting the furnace a few times for diagnostics, I noticed I started to feel light headed, and got a slight headache, nothing much but enough that I noticed it, and decided I might want to be safer than sorry. shut everything down for a little bit, opened a window and went outside. after about ten minutes I felt better and continued to work. May have been nothing, but at least with one of these I will know long before I feel symptoms.

Not taking the chance anymore.

My Sensit P100 rings when i stand behind vehicles that are running. It makes one think how much CO we are exposed to on a daily basis.

JohnNY said:

I bought this alarm for $150 on Amazon after seeing it clipped to every NYC Boiler Inspector's clothing. It will now be standard equipment for my field techs and myself just as it is for the inspectors.

...

I'm considering this a close call.

I couldn't agree more with the importance of always wearing a reliable CO monitor when entering a boiler room, or any space containing combustion equipment. There are two things I'd like to point out, especially to the OP:

- I recognize the model of CO monitor in your picture, we used to use them at my old company, before I took over managing our equipment and replaced them with better ones. I consider those to be complete junk- We had 3 of them, all about a year old I think (no more than two), and all failed calibration and had various errors. This is not professional or reliable equipment, and for something as critical for your own safety and that of your customers as CO monitors, it's not worth cheaping out.

There are plenty of good monitors on the market, my favorite and the one I highly recommend are the Drager PAC 5500, which you can find online for a little over $300. I've also used the Testo 317-3, the problem with that one is that it's too easy to hit the mute button or turn it off by accident. The Drager has a loud alarm which can't be turned off, as well as vibration and flashing lights.

- While 94ppm CO is very serious, and a legitimate emergency situation, you were probably in no immediate danger at that level. While sources and individuals vary, to put that in perspective, it would take several hours of exposure at that level to produce a "light headache". It's certainly better to overreact than under-react when it comes to CO, but I've learned the hard way that some people can get very upset when you're a little imprecise about describing the level of danger, and throw around the term 'life threatening' for levels that aren't quite there (although I think it's fair and prudent to consider any back-drafting situation as potentially life threatening, regardless of the CO level at that moment)..

Here's some info about CO levels you might find useful. The chart on the left is from the Testo manual that came with one of their combustion analyzers. i don't remember where i found the chart on the right. Since the sources are a bit hazy, I wouldn't fully trust either one as the definitive numbers, but it should give you a ballpark about the level of danger from short term exposure to various CO concentrations.

(edit: I originally posted that the 3 cheap CO monitors we had were "less than a year old", I meant to say about a year old, I don't remember exactly).

70 PPM (measured ~2 hours after exposure began) had a noticeable effect on me.

The Sensorcon Inspector (photo above posted by @Stephen Minnich) can be calibrated -- and has a fairly decent UI which prevents unintended silencing or shutoffs.

@SWEI, the Drager PAC 5500 units can be recalibrated, but you have to send it in, unless you have enough units that you want to invest in some pricey docking stations, software, and other equipment. But you can replace the battery yourself (which I have yet to have to do).

@JohnNY, I suppose there are smaller units available, but I like the size of these. I clip them to a pocket or my belt, or sometimes to the outside of my backpack.

Just last week, I was standing in the hallway of an apartment building, and out of the blue my CO alarm started beeping (loud enough to get the attention of several residents). It showed about 56ppm just for a few seconds before returning to zero, I think because someone opened a door. After checking several apartments, I identified one apartment that consistently had about 16ppm, +/- about 5, resulting from her oven. I advised her to open the windows, shut off the oven, and informed the management that they should have the oven serviced or replaced. She apparently had a functioning CO alarm, but as we know those don't go off until the level gets pretty high..

Needless to say, the resident was very grateful that I found the potential safety hazard. I've had the alarm go off many times, though I think this was the first time it reached the low alarm threshold (35ppm) outside of a boiler room.. I can't recommend the Drager CO alarms enough.. (I have no affiliation with them, I just appreciate tools that work well)

Steamhead said:

Answerman said:

FYI @delta T , I routinely find boilers with over 2,000ppm, but 0ppm ambient. It's not uncommon, at least not with the large, old, boilers I find in NYC multifamily buildings. It's certainly not good, and I always consider it a potentially hazardous situation (as well as a sign of poor combustion efficiency), but a high CO in the stack will only affect ambient CO if there is also back-drafting.

Which happens if the flue gets blocked or restricted. That's why our company doesn't tolerate such high CO levels. Fortunately, it's pretty easy to get them down with a few adjustments or some cleaning, or both.

On one particular boiler that was overgassed, causing over 2500 ppm CO, the chimney was also blocked with about 18 inches of crap- including a couple of dead crows. You could smell the aldehydes coming out of the draft hood about 10 seconds after the boiler lit off.

Oh, and a tech from a different company had told him this was normal. You can't fix stupid.

Jstar wouldn't allow over 55ppm on my boiler. I even tried to get him to go closer to 100, he wouldn't do it. Now it's likely close to 0 because I put everything back to stock, I didn't like the extra steam pressure. I was running close to 1" !