CO at the Bath Fixtures?

I had a really interesting (to say the least) experience today. I was doing my bathroom inspection and I started to feel dizzy. The furnace was off but a gas appliance(fireplace) was on so I decided to check it. I was upstairs in the master bathroom. The only thing I could think of is the chimney must come through a duct chase near the bathroom and it must be leaking ( I suspected this because my CO detector showed levels above 10). A quick scan with the IR cam told me the chase was elsewhere so I quickly ruled it out as a source. I turned on the furnace and checked the registers for CO - Nothing above 5. All the while the hot water was running in the tub. I didn’t think much of until I sat next the tub with my CO meter. When I did the meter jumped to 50-100-150. I left the room when I saw it hit 600 plus. I went around and checked all the plumbing fixtures on the hot side. All of them had high readings of CO when operated. I stopped after the kitchen because the CO was really making me dizzy and I vomited. I called the listing agent and the local utility to report the problem.

Anyone ever heard of this? The only thing I can think of there is dissolved CO in the water which is compressed while in the tank and the released when it hits ambient air pressures. The water heater was an AO Smith ProMax manufactured in 2004.

Wow, crazy. Nice to hear you are ok Steve.

Could there be a defective burner adding exhast gas into the water???

Is the house on well water? There could be a natural gas formation underground when the water is heated it will give off CO.
There was a local well here that blew up last week. They are drilling sideways here to tap the marcelous natural gas veins.
They just vented two streets worth of wells and are trucking in water to connect to all the houses. see or wbng tv Binghamton NY

It shouldn’t have anything to do with the water heater, or any other appliance for that matter. Remember, the plumbing system is pressurized.

The only time I’ve heard of a similar occurrence was on a house with a well. It was in relatively close proximity to natural hot-springs.

I don’t recall the specifics.


Was it a well or municipal water supply?

Definitely on a municipal supply.


Did you test this co with “cold” only?

The problem only presented itself when operating the hot fixture or it at least it seemed so. I don’t recall if I tested it on the cold side - my brain was getting kind of fuzzy…

Is it possible that the flue pipe has a perforation and flue gases are leaking into the water and dissolving? The combustion chamber was sealed as this was a high efficiency water heater

If flue gases are getting into the hot water supply, then there would have to be a leak somewhere in the water heater jacket.

I’d want to see if the co is on the cold side also…

This is a vacant house. It is has been unoccupied for 5 months or longer. The water was shut down just prior to my arrival. I do not know if the tank was drained and re-filled or not. The combustion chamber was closed. There was no signs of leakage at the tank. It is possible that there is some water in the combustion chamber that has not leaked but it couldn’t be more than an inch or so…

I suppose that it could be possible for the flue to have pinholes which is uncommon and unheard of. But if this were the case, water would be dripping on the top of the burner.

Did you get an answer from the utility company you contacted?


This is very interesting. You mentioned it was a vacant house. Is it possible that what you encountered was Hydrogen Sulfide buildup in the water heater and that it interfered with your carbon monoxide detector?

You describe hypoxia as your symptoms and I am wondering if this was due to high Hydrogen Sulfide levels.

Below is an article on sensor technology and anomalous CO readings due to Hydrogen Sulfide.

I would contact the manufacturer of you CO detector and find out if their sensor is subject to this error.

** Toxic Sensors

  1. Electrochemical (Wet Chem) Toxic Sensors

** These sensors react to a specific chemical (substance). Chemically specific sensors are available for chlorine, ammonia, carbon monoxide, carbon dioxide, nitrogen dioxide, nitric oxide, hydrogen cyanide, hydrogen sulfide, sulfur dioxide and hydrochloric acid. The manufacturer’s technical information will indicate what sensors are available for their unit. ( Figure 3).

**The electrochemical sensor housing contains two (and sometimes three) electrodes sitting in a liquid solution (either a base or alkali, depending on what the sensor is looking for). The housing is covered by a Teflon membrane that keeps the fluid in the housing yet allows air in. As air molecules enter through the thin Teflon membrane, the fluid will react with a specific substance if found. When the detector is working a small current passes between the two electrodes. Any change in the fluid’s density caused by a reaction to the substance in the air will affect the density of the fluid and change the amount of current passing between the two electrodes. The current then passes through a temperature compensating circuit. The electron flow is then read as a specific amount of the substance. The manufacturer creates a Wet Chem Sensor’s ability to detect specific types of gases based on the choice of membrane, the number of electrodes, the alloy of the electrodes, the alloy of the electrode (gold, lead, etc.) and type of electrolyte fluid.
These sensors have very good linearity which makes them very accurate for the substance they will react to. They can measure either large or small quantities and these sensors have a typical life span of approximately 1 year.
As with all sensors, Wet Chem sensors have their limitations. The fluid can freeze when left in environments having temperatures lower than 0 degrees C. They are also adversely affected by altitude. Air pressure at sea level (14.73 psi absolute) is the force required to induce the air into the sensor. As one rises in altitude, the less force is available to push the air into the sensor, thus reducing the accuracy of the reading. Some substances, (e.g. moisture) affect the sensor by changing the make up of the fluid, thus reducing the amount of electrical resistance which impacts the reading. Check the manufacturer’s instructions to see which substances will affect the sensor.
Abnormal readings are another issue with regards to Wet Chem sensors. Abnormal readings are generally readings that don’t make sense. For instance you are working in a sanitary sewer and your instrument is showing a CO reading of 300 PPM (current TWA in Ontario is 35 PPM) and a low reading (below the TWA of 10 PPM) of hydrogen sulfide. What you likely have is an interference from the hydrogen sulfide. Some electrochemical carbon monoxide sensors are subject to interference from low levels of hydrogen sulfide. The knowledge that carbon monoxide is not a common occurrence in sanitary sewer applications (whereas hydrogen sulfide is) would lead you to consider that you are probably having an interference problem.
Awareness of the hazards in your workplace, some basic understanding of chemistry, knowing what interferent gases adversely affect your unit and strict testing protocols will minimize this problem

Thanks Michael. I will call them today. I didn’t get the classic “rotten egg” smell. I have experienced that on new water heaters. In this case, there was no clues that there was a problem other than my symptoms and paranoia.

Dave- I agree. It is a long shot. The utility never did get access because I left the property and the agent did not go out to let them in. If I get any information from the agent or utility I will share it.

The model is a Bacharach Snifit 50. Here are the specs:

  • Range: 0-1,999 ppm
  • Resolution: 1 ppm
  • Display: 3-1/2" display with yellow-green backlight (Snifit® 50 only)
  • **Sensor Type:**Electrochemical (specific to CO)
  • Sensor Calibration: Factory calibrated on 100 ppm
  • Sensor Accuracy: ±5% of reading

According to the manufacturer rep the CO detector is sensitive to hydrogen on a one to one basis. Therefore, if there was any hydrogen in the water that is released when it hits ambient air it would elevate the readings. He told me that the area would have to be analyzed with a CO detector that is not sensitive to hydrogen (i.e. Bacharach Fyrite combustion analyzer).

This seems to make sense for the detector but doesn’t account for my symptoms (which were admittedly generic). However, I did feel better when I went outside to get some fresh air. I also had a lingering headache for 3-4 hours after the inspection.

I am going to recommend that my client have the building tested by a professional that has a comparable product to the Fyrite. I will let you know if I learn more.