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Furnaces and Carbon Monoxide: Why is there a risk?

Carbon monoxide (CO) is produced whenever a fuel (such as wood, gasoline, coal, natural gas, kerosene, etc.) is burning.  If your furnace, water heater, or boiler malfunctions, or the vent becomes blocked, carbon monoxide can be leaked into your home.  CO poisoning can occur in any situation where a person is exposed to an incomplete burning of fossil fuel, and it can be fatal.

How does carbon monoxide harm you?

Carbon Monoxide prevents oxygen from being used in your body and can harm the central nervous system, and even your heart.

Everyone is at risk of being poisoned when exposed to the gas but individuals with existing health problems such as heart disease, lung problems, are at risk of succumbing faster.  Infants, children, and pregnant women are also at a higher risk.

Gas Furnaces:  Cracked Heat Exchangers

The most common reason for a natural gas furnace to leak carbon monoxide is from a crack in the heat exchanger.  The heat exchanger is the metal wall or tubing that is heated up when the burners are ignited. The inside of the heat exchanger allows the toxic flue gases produced from the burners to exhaust out through the furnace flue. The outside of the heat exchanger is where the cold air passes over, becomes warmed, and is blown throughout the ductwork of the home. The heat exchanger is the only wall separating the toxic flue gases from the supply air. If a crack develops in the heat exchanger, there is a potential for carbon monoxide gas to leak over to the supply side and be blown throughout your rooms. Since carbon monoxide gas is odorless, the human senses will not detect its presence.

If there is a crack in a heat exchanger there may not be carbon monoxide present right away.  A very dangerous misconception is that if there is a crack in the heat exchanger but no carbon monoxide present at the time of the check up, the furnace is still safe to run.  In fact, at any time during the use of the furnace carbon monoxide may suddenly and without warning appear.  As the furnace runs it begins to burn dirtier which can create the gas.  A crack in the heat exchanger is a pathway for the gas to escape through, and leak out into the home.  As the gas goes through the crack, and the metal continues to heat up, the hole can grow larger quickly!  What may have been only 1 or 2 parts per million, can rapidly become 300 parts per million or higher!  Any HVAC professional telling you that a unit in this condition is safe to run is putting everyone in your home at risk!

Safety, Longevity, and Furnace Maintenance

Gas forced air furnaces last approximately 15 years, some more, some less, depending on how well maintained the units are. Some conditions that may shorten the life of your furnace are: the evaporator unit of the air conditioner leaking onto the heat exchanger causing it to rust out, dirt/dust building up on the high-limit control switch forcing your furnace to turn on and off more frequently, a dirty filter that drastically reduces air flow which also will force your furnace to kick on and off more, or dirt on the burners producing inefficient flames causing excess soot buildup on the heat exchanger. If a furnace is poorly maintained, it is not uncommon to find a crack in the heat exchanger much sooner than 15 years.

Since a heat exchanger is made of metal and is constantly being heated up over and over again, the heat exchanger will eventually fail.  Each time, the metal expands as it warms up and contracts as it cools down.  Eventually the metal fails and a crack is formed.  A crack will always develop in the heat exchanger.  How soon depends on the conditions it has been subjected to over its lifetime.  To prevent emergencies a furnace tune-up and heat exchanger inspection should be performed annually by a licensed HVAC (Heating, Ventilation, Air-Conditioning) professional.

To prevent premature damage to the heat exchanger makes sure there is sufficient air flow to your furnace.  Keep return registers from being blocked, keep the furnace filter clean, and make sure there is plenty of open space around the furnace and water heater.

Test Your HVAC Company:

Not all heating and cooling companies are created equal.  To ensure the safety in your home ask the company you choose questions about their carbon monoxide policies, tools used during the tune-up or inspection, whether or not a heat exchanger inspection is included with their tune-up price.

Ask them:

  1. What does your company consider as a safe level of carbon monoxide in doors?

Answer:  NONE, or 0 parts per million.

**There is no agreed upon safe level of carbon monoxide indoors.  And according to the United States Environmental Protection Agency; no standards for CO have been agreed upon for indoor air.  The U.S. National Ambient air quality standards for outdoor air are 9ppm for 8 hours.

  1. Ask them if they scope heat exchangers during their tune-ups or inspections.

Answer:  Companies that are concerned about safety will include a heat exchanger inspection at no additional cost.

3.  Ask them what tools they use to inspect the heat exchanger.

Answer:  To do a complete safety inspection the following tools should be used:

a)     Heat Exchanger Scope/Camera and Heat Exchanger mirror (a mirror alone is NOT going to catch all cracks)

b)    Combustion Analyzer or Carbon Monoxide Detector

c)     Gas manometer

d)    Gas detector


Virginia Natural Gas says:

Inspectors had “red-tagged” the home’s furnace as defective. About 10 years ago, Norfolk asked to be notified only when inspectors found gas furnaces with cracked heat exchangers. Norfolk says:

If Virginia Natural Gas had turned off the home’s gas, the city could have declared the house unfit for habitation and padlocked it because it would have had no heat or hot water. Municipal officials told Virginia Natural Gas more than a decade ago not to notify the city about some “red-tag” warnings, abandoning a policy that could have prevented the carbon monoxide deaths of four persons, a company spokesman said Wednesday.

Ed Ware, director of public affairs for Virginia Natural Gas, said the city asked to be told only when gas company inspectors found gas furnaces with cracked heat exchangers.

Before the city made its request – between 10 and 12 years ago – the utility supplied reports of all “red-tag” inspections, including those that uncovered faulty furnace exhausts like the one that caused a back-up of carbon monoxide at a rented, two-story house at 208 W. 30th St., Ware said.

“We were complying with their information request,” he explained.

Sherman Edmondson, Norfolk’s assistant director for codes administration, angrily disagreed Wednesday that the city should accept blame for the tragedy.

Edmondson suggested that the deaths could have been averted if the gas company had stopped service to the home.

“If Virginia National Gas had turned off the gas,” Edmondson said, “the building would have been unfit for human habitation. No heat and no hot water. Then we could have padlocked the building.”

On March 11, 1993, the gas company “red-tagged” the home’s gas furnace, warning residents that the heating system needed to be repaired before it was used again. Although the utility turned off a valve through which gas flowed to the furnace, it did not shut off gas service to the dwelling.

Someone apparently turned the valve on again and started using the furnace. Officials said they found the furnace’s chimney blocked by a buildup of fallen bricks and soot, causing the back-up of the deadly, odorless gas.

Julia Dempsey, 38, was found dead late Monday afternoon on the second floor of the residence along with two of her children, Lakisha Dempsey, 15, and William E. Dempsey, 5. William Staton, Dempsey’s 41-year-old fiance and the father of William Dempsey, also was found dead.

Three of the bodies were found on or near beds. The 5-year-old boy was found in a hallway.

The bodies were found by another of Dempsey’s children, 17-year-old Mashuana, who had returned home Monday afternoon after spending the weekend at another residence. Police believe the family may have died as early as Saturday, the last day they were seen alive.

Edmondson said Wednesday that city building inspectors tried several times in March to get into Julia Dempsey’s home to inspect the installation of a new water heater. Each time, she said, no one came to the door.

Edmondson said the city is notified whenever work is required under a building permit, such as the installation of a new water heater. The gas company’s red-tag warning had nothing to do with a building permit.

Meanwhile, a city councilman on Wednesday said the city needs to revamp its method of building code enforcement to ensure that Monday’s carbon monoxide tragedy is not repeated.

Herbert Collins, who represents much of central Norfolk and parts of 30th Street where Monday’s accident occurred, promised to introduce an ordinance that would attack the problem.

“We have to have some kind of code enforcement that won’t tolerate those things happening,” Collins said. “There is just not enough code enforcement at a lot of these rental properties.”

Edmondson said her staff has developed a new plan. She declined to go into detail until the council is briefed.

Family members said following the tragedy that Julia Dempsey had repeatedly complained to the landlord about the furnace. The building’s owner, Suzanne Marshall, of Virginia Beach, could not be reached for comment Wednesday. Fire investigators are continuing their investigation.

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