Having been in the mechanical service business for more than 22 years, I’ve had my share of carboned up boilers to contend with. In most every case, the occupants of the dwelling were unaware of the potential dangers that existed, and didn’t even know that a problem had occurred.

Of all the sooted up boilers I’ve seen, a reasonable and logical cause explained each and every case. One way or another, the incomplete combustion of flammable gas is what is responsible for the production of CO.

The intent of this article is to make all service technicians who work on or around boilers and other gas-fired appliances aware of the following:

  • What conditions cause carboning and carbon monoxide production.
  • How to eliminate those conditions.
  • How to quickly identify an existing problem.
  • What measures should be taken to avoid further carbon production.

Although I’ve seen many ways for carbon and, consequently, carbon monoxide to be produced, I’m positive I have not seen them all. Experience will show that just when you think you know everything there is to know about a given subject, Mother Nature comes along and shows you something you hadn’t counted on. But here are some real experiences I’ve had:

The Rain Forest Syndrome

I’ve had numerous carbon monoxide cases involving low mass copper finned tube boilers used for everything from pool heating to hot tub heating and even house and domestic hot water heating. What typically happens in these cases is the boiler’s heat exchanger is exposed to operating conditions well below the minimum allowable operating temperature of the boiler system.

Typically on domestic hot water heating systems, the cold water was introduced into the boiler at its inlet. During peak loading, the flue gasses are cooled down well below their condensation point. When these flue gasses condense and drop off the heat exchanger, they drip onto the burners below. This dripping, or what I typically refer to as a “rain forest in yer fire box,” causes the flame to spatter, and burn dirty. This dirty burning causes wet carbon deposits on the copper finned heat exchanger.

Eventually, the heat exchanger flue passages become completely plugged, and major “roll out” from the burner tray begins. In most cases, the roll out is serious enough to cause the control wiring to short out to ground, and the primary boiler transformer fails. In most cases, that is.

In the case of newer boilers equipped with roll out protection gear, sometimes the roll out occurs in such a manner that the protection switch does not “see” the roll out. Consequently, someone gets sick, or worse, dies. Until a roll out safety switch that monitors the entire width of the combustion chamber opening aperture is invented, this will continue to be a problem. (Hello, GAMA, are you listening?)

The Case Of The Overbearing Kitchen Exhaust Fan

I once had the unfortunate experience of being partially poisoned by two large boilers in a hotel mechanical room.

I was in the mechanical room installing an energy management system. Meanwhile, I wasn’t really paying a whole lot of attention to the combustion process occurring alongside me. Fortunately, a hotel engineering employee was aware of the problem and checked in on me — only to find me passed out on the floor.

Further investigation proved the following: In a large production kitchen located 50 feet from the boiler room was a powered hood exhaust system. This hood also had a makeup air system that was untempered. When it was cold outside, the makeup system dumped cold air directly onto the necks of the chefs on the cooking line. The head chef convinced someone from engineering to shut it off.

However, removing 10,000 cubic feet per minute caused substantial negative pressure to be exerted on the building as a whole. The negative pressure was measured at a negative 3.5 inches of water column. The boilers in the mechanical room were a natural draft type of boiler whose breaching pressure is generally negative 0.02 inches of water column. Guess where the flue gasses were going? Not outside like they were supposed to, that’s for sure.

And before you ask, yes, there was outside air available for combustion. However, it had been partially closed off due to cold air flowing into the mechanical room and freezing the pipes. As a result, the makeup air system had to have a makeup heater installed on its intake in order to deliver tempered air to the exhaust hood. In addition, the system was interlocked into the exhaust fan to insure that one could not run without the other. Finally, the mechanical room’s air had to be “isolated” from the building’s air. This entailed installing tighter doors, seals and caulking to shut the annular space between the ceiling and the walls. If it had been isolated to begin with, none of this probably would have happened.

These Things Need Air?

I once had a commercial 80-gallon water heater located in a closet. This closet got its combustion air from two 6-inch vents coming through the ceiling. At some point in time, someone decided the cold air that came through the vents was too much. As a result, they installed sheet metal caps on the combustion air vents to stop the incoming air. Evidently a pipe had frozen in the closet at one time.

We were originally called in to figure out why the pilot kept going out. Using my finest tunnel vision glasses, I replaced the thermocouple and thermocouple magnet. The next day, I got the call — no pilot again. This time, I took my tunnel vision glasses off, opened my mind and my eyes, re-lit the pilot, stayed inside the closet with the door closed, turned off my flash light and observed the following:

“Boy it’s dark in here! Sniff, sniff. Hmmm, that smells like partially burned natural gas.”

Much to my surprise, I found that when the water heater had completely exhausted the small closet space of all its air for combustion, it began pulling combustion air down the flue pipe. Guess what? You can’t sustain a flame in the presence of carbon dioxide. The main burner and the pilot eventually was snuffed out due to a lack of oxygen.

I’ve seen other cases where similar conditions existed, and someone installed an electronic ignition system. When the pilot gets snuffed and an electronic ignition system is on line, the system keeps going back for a re-trial for ignition. Short cycling. The pilot and main burner flame catches, snuffs out and re-tries again. Now between cycles, enough oxygen seeped back into the room to allow combustion to start, but not enough to sustain continuous combustion. Consequently, carbon and carbon monoxide are produced, plugging the flue gas passageways and causing major flame roll out. This continuous, undetected roll out is what kills people. To solve this problem, thermal siphon traps were installed on the combustion/ventilation air.

Deadly Dust

Quite often, during the course of home construction during the winter, the newly installed heating system is called upon to provide temporary construction heat. Everything goes along OK during the final days of the framing stages. The problem pops up during insulation and sheet rock finishing.

You see, when an appliance combusts gas, it consumes a substantial amount of air. If there are particles of dust floating in the air, these particles mix with the gas being combusted and retard the combustion process. The carbon accumulates as a dry carbon on the heat exchanger surfaces, eventually blocking the flow of gasses up through the boiler.

If and when dust will be in suspension — i.e., insulating, sheet rock sanding, acoustical applications etc. — gas-fired appliances must be shut off. Either that or a guaranteed clean source of combustion air be made available to the appliances. Typically isolating the boiler room and providing it with the required amount of combustion air insures a clean burn. Notify your builders in writing so that if and when it does occur — and I guarantee you it’ll happen —your liability is limited.

Speaking of limiting liability and exposure, did you know that carbon dust is still a dangerously explosive material? When the dust gathers in suspension in the open air under certain concentrations, you have a bomb the size of that room. All it needs is a source of ignition and boom, it’s all over. Make sure that your employees are using a HEPA vacuum or require that the vacuum be kept outside the building. Also, make sure your employees are using NIOSH-approved ventilators.

The Drive By Test

This is probably the easiest way to spot a killer, but requires a lot of tact on your part in delivering the message. As you’re driving down residential streets in a known natural gas area, look for blackened flue pipe terminals. If you see a vent terminus, and you are reasonably sure it is not connected to a fireplace, and the vent cap is blackened by soot, you got yourself a problem. The next step is the hardest part of saving some lives. Do you:

A. leave a note on the person’s door telling them that you know they have a killer in their basement.

B.tell them in person that you know they have a killer in their basement and you want to show them where it is and how it can be eliminated.

C. shut off their gas meter and leave your business card in their door telling them to call you immediately.

D. tell their neighbors to tell them that they have a killer in their basement.

There are many correct answers. If it’s a relative of yours, C would be appropriate. If it’s a neighbor you don’t like, maybe D or A. If you can convince the homeowner that you’re not kidding them, B is the most appropriate. If B isn’t possible, consider A buffered with D. The neighbors can probably convince them, if you can convince the neighbor. If they don’t trust you, tell them to call their local gas utility, and the utility will yank their gas meter.

I’ve experienced this drive by stuff before, and it’s not easy. You are somewhat out of place doing a cold call on the homeowner. Be professional, apologetic, courteous and downright serious. We’re talking about a life and death matter here. You shouldn’t have trouble convincing them that you know what you’re talking about. You are after all, “The Expert.”