Iowa State University Extension

Investigations of Carbon Monoxide Cases Reveal Many Problems

Thomas H. Greiner, Ph.D., P.E.
Associate Professor
Iowa State University Extension Housing Engineer

Carbon monoxide (CO), a colorless, odorless, tasteless gas, becomes a killer when linked to faulty heating equipment. Concern about this lethal killer reaches new highs as increasing numbers report near misses from CO poisoning. This raises the questions, "How can I protect my home and family from the danger?"

As state housing engineer with Iowa State University Extension at Ames, I recommend yearly checks for all heating appliances and the installation of alarm sounding carbon monoxide detectors. The detectors indicate when life threatening levels of CO are present. Finding out what causes CO incidents is not always clear cut.

Obvious reasons include cracked heat exchangers in the furnace or blocked or disconnected venting systems. But, many causes escape detection without the use of sophisticated equipment now available. This equipment includes a blower door to determine the tightness of the structure, a micromanometer which determines very small pressure differences, flow measuring equipment, carbon monoxide detectors, and combustion analyzers.

During the past two winters I used the above mentioned equipment to determine reasons for several unexplained carbon monoxide incidents. Six case studies from my investigations follow.



An entire family found themselves in the emergency room being treated with oxygen for CO poisoning. A heating contractor investigated the problem. He installed a higher chimney and larger screens to keep ice from forming around combustion air inlets. Carbon monoxide detectors were also installed.

The detectors went off, the contractor was called back in and this time determined the fireplace needed a glass door and more combustion air was required by the furnace and the fireplace. Even with these improvements the detectors continued to intermittently sound.

At this point the home owner contacted my office for additional help. Investigation revealed a home with so many exhausting appliances (seven bathroom fans, a kitchen fan, fireplace, clothes dryer, water heater and two furnaces), that four combustion air openings and leaks in the house could not furnish adequate combustion air. My recommended solution required replacing the existing natural draft furnaces, which require air from inside the house, with sealed combustion units which provide their own air through sealed plastic pipes. This solved the problems.



Another case involved a family experiencing flu-like symptoms over several weeks. A week prior to the emergency call, the daughter suffered convulsions and seizures, often symptoms of CO poisoning. At 3 a.m. the father woke extremely ill. He tried arousing other members of the family without success. Completely disoriented and passing in and out of consciousness he searched for a phone. Two hours later he managed to dial 911 before again passing out. Emergency workers found him collapsed over the phone. The entire family received treatment at a local emergency room.

The culprit in this case was the furnace, which, during a remodeling project, was enclosed in a small room with no combustion air openings. The problem was compounded by a disconnected cold air return which depressurized the furnace room, drawing cold air back into the house through the chimney and spilling all the combustion products into the home. Although the furnace operated several years under these conditions, as the burners built up dirt and burned less efficiently, CO levels increased to the point of severe poisoning. Both the carpenter and heating contractor were unaware of the dangers of the disconnected cold air return.



A couple failed to respond to calls from family and friends. Upon entering the dwelling both were found dead. The culprit--carbon monoxide. In this case a multitude of problems contributed to the deaths, including a high capacity boiler and water heater located in a small space without sufficient combustion air. The undersize vent system did not have sufficient rise or height and was rusted through. Cupolas on the roof depressurized the attic. Lack of soffit vents and a loose ceiling allowed the depressurized attic to depressurize the living spaces. The basement door had been removed, allowing the depressurization to continue into the basement. Carbon monoxide was exhausted into the home.



Soot in the house and hot flue gases escaping at the draft diverters of the furnace and water heater indicated a severe backdrafting problem. The heating contractor failed to identify the exact cause but did correctly install a new sealed combustion furnace to replace an old outdated model. Follow up testing revealed the cause to be an attic vent fan which, when operating, depressurized the attic and pulled air from the house. This in turn depressurized the basement, pulling air DOWN the water heater vent. An additional factor was new siding placed over the attic gable vents and restricting air flow into the attic. Obviously the siding contractor did not realize the danger in which he placed the homeowner. The heating contractor did not check for depressurization. Until the siding problem is corrected, the homeowner will not use the fan.



This case illustrates the lack of training and education of some heating contractors now being asked to locate and deal with an increasing number of reported CO episodes. The family purchased a battery operated CO detector during the last heating season. It went off. The contractor arrived and found no problems with the furnace or the water heater. The family assumed the detector faulty and returned it to the manufacturer who replaced it. The furnace and water heater were again inspected by the heating contractor at the beginning of this year's heating season. No problems were found. With the onset of cold weather the detector went off. Not trusting the single detector, the family purchased two more. Now all three detectors intermittently indicated the presence of carbon monoxide.

My office placed monitoring devices in the home and by 6:30 p.m. recorded readings of 8 parts per million in the home and 3,000 parts per million in the furnace, a dangerous level. A call was made to the heating contractor, who obviously had no idea how dangerous the readings were. He convinced the homeowner to wait until morning for a service call. When the service man finally arrived the next morning he visually checked the flame, which he pronounced to be okay. He had no plans to check for over-fueling and when asked, did so with a defective gauge. When convinced to double check using my gauge the results indicated a dangerous over-fueling condition, the result of a defective gas control. The over-fueling caused incomplete combustion and extremely high levels of CO production. His solution was to reduce the firing rate of the furnace by partially closing the furnace shut-off valve, which produced another dangerous situation. A defective gas control requires the furnace be shut down immediately. A sealed combustion furnace was installed. Had the homeowners depended on the heating contractor, they would have remained convinced their CO detectors were defective and continued to be at risk of CO poisoning.



The couple received a carbon monoxide detector as a gift and the detector went off. The couple called 911. The fire department arrived, found readings of 28 parts per million and determined dirty pilots on the kitchen stove were the cause of the problem. To prevent further problems, the couple purchased a new gas kitchen stove with electronic ignition and sealed burners.

Dr. Kenneth Wiggers, President of American Environmental Services, Inc., Ames, participated in several of the investigations.



Carbon monoxide cases often require a great deal of detective work. When simple answers are not available, it leaves the homeowner concerned and confused. Training and education in CO detection is not always required or available to heating contractors. In many locations there are no mechanical codes, nor are contractors required to be licensed. Fire departments are called in to take reading on instruments which record only the presence of CO with no clues as to its cause. Often the fire department is called after windows and doors are opened and the carbon monoxide dispersed, resulting in no readings at all. Some medical personnel are not aware of the possible extent of the problem and may misdiagnose what on the surface looks like a simple case of the flu.

Carbon monoxide symptoms mimic other medical conditions such as the flu, heart attack and muscular sclerosis. Carbon monoxide kills by replacing oxygen in the blood. High levels kill in a short period. Moderate levels, because CO is a cumulative poison, can cause misdiagnosed health problems or even death. Low levels over a long period can cause health problems, especially for patients at risk. Exposure can result in long lasting or permanent effects including brain damage. After exposure, merely removing the victims from the area is not enough. Some form of medical attention is required. The most effective treatment uses a hyperbaric chamber, where, under pressure, the CO is quickly replaced with oxygen.

While on faculty improvement leave in England, I spent time with British Gas observing their efforts to reduce carbon monoxide risks. England recognizes the problem and now requires persons who deal with CO situations be trained and licensed. I returned with copies of their medical training video which I supplied to several hospitals here in Iowa. Fortunately for Iowans, several of our hospitals are equipped with hyperbaric chambers and trained to handle CO poisoning cases.

Long Term Solutions

  1. Newly installed gas heating appliances must be "sealed combustion" or "direct vent," where exhaust and air supplies are completely sealed from inside a home. As an added bonus the units are energy efficient and reduce fuel costs.
  2. Statewide licensing of heating contractors, with appropriate requirements for education.
  3. Continued awareness of the potential for carbon monoxide poisoning and the need for appropriate responses including the short term steps listed below.

Short term steps

  1. Heating appliances must be checked at the beginning of EACH heating season by a QUALIFIED heating contractor. Checks should include making sure fuel is burning completely, that all products of combustion are adequately vented to the outdoors, and that exhaust appliances do not cause backdrafting.
  2. UL-listed carbon monoxide detectors should be in every home. Chicago requires CO detectors, and already reports many lives saved. Detectors which sound must be taken seriously. The alarm indicates a problem with CO, not a problem with the detector. The heating contractor should answer two questions for the homeowner: 1) Why was CO produced? and 2) Why did it collect in the home instead of venting to the outdoors? Without definitive answers to both questions the CO problem can not be solved.
  3. Backdraft indicators should be used on all naturally drafting appliances.

Carbon monoxide, a colorless, odorless, tasteless gas, each year claims lives and causes illnesses for many more. High levels kill in a short period. Because CO is a cumulative poison, moderate levels cause health problems and may lead to eventual death.

Original web publication date: October 1996

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