Carbon Monoxide Warnings

The Carbon Monoxide Checklist has a list of the most common carbon monoxide dangers. Make sure you’ve read the list and understand that a simple lack of knowledge can be fatal.

The Top Five Carbon Monoxide Killers


1. Vehicles Left Running in Garages

CO deaths from vehicle left running in garage

CO deaths from vehicle left running in garage

Never, ever, leave a car other vehicle running inside a garage. Even with the garage door open carbon monoxide can seep inside the home.




2. Gas-powered Generators Used Indoors

Portable Generator

Portable Generator

Never use a gas generator or any gasoline engine inside a garage or home (or other structure like a utility shed or barn.) Gas engines put out very high levels of carbon monoxide when they operate. Even a very clean-burning engine will create enormous amounts of carbon monoxide.



3. Charcoal Grills Used Indoors

Charcoal Grill

Charcoal Grill

Never use any kind of charcoal grill indoors. Every form of charcoal fire puts out very high amounts of carbon monoxide. If the charcoal is warm, it is emitting carbon monoxide. A flame or smoke doesn’t have to be visible for the coals to fill an area with CO in a few minutes.



4. Gas Ovens and Stove-top Gas Burners Used For Heat

Stove_LineDwg3When there’s a power outage or a problem with your furnace it is tempting to turn on your gas stove or oven to heat the house. Do NOT do it!!

Gas burners and ovens require a large amount of oxygen to operate safely. When your home is closed up tight to conserve heat, there is no way to replace the oxygen used by the burners. When the burners begin using air that has been depleated of oxygen, they create very high levels of carbon monoxide in a short period of time.

The problem is not a defect in the stove or oven, it is the lack of oxygen that causes carbon monoxide to reach dangerous levels in a few hours.



5. Unvented Heaters Used in Confined Spaces

Non-vented gas space heater

Non-vented space heater

Small propane heaters, infra-red heaters, “Coleman” lanterns, kerosine heaters and small propane cook stoves all share a common characteristic … they ALL will create very high levels of carbon monoxide if they are used in a small space like a camper or tent or mobile home or vehicle.

These devices require large amounts of oxygen to run safely. Deprived of oxygen, they will create carbon monoxide in large quantities in a short period of time. If you try to heat a tent or camper shell with a propane or kerosine heater, you’ll be dead by morning unless you have sufficient fresh air entering the enclosed space.

Lack of Combustion Air and an adequate flue –
The Real Causes of CO Problems in Homes

 Potential Reasons for Flue Back Drafts

Sources_of_CO_backdraftClick on Picture for Larger Image in New Window

Picture a house as a big box with a lot of holes in it.  The roof has holes like exhaust fan vents and flues and sewer vents.  The walls have holes like windows and doors.  Even the floor has holes like floor drains and sewer connections.

If every window and door is closed tight, all the floor and sink drains have traps that are filled with water, then the only way air can be removed by an exhaust fan or flue is for more air to enter from somewhere else.  When the house is tightly closed and has good weather stripping, the only place for air to enter the home is via the flue.

This becomes an issue in the middle of a cold winter.  To save fuel and maintain temperature all windows and doors will be tightly sealed.  Trips in and out are at a minimum.  If during periods like this someone runs their gas drier, there is a good chance of the drier causing the furnace or water heater flue to back draft.  The closer the drier is to the flue, the easier it is to pull air down the flue.  The dryer can easily exhaust enough air to cause the house to have “negative” air pressure.


The dangerous part occurs when the water heater or furnace (or any gas appliance) begin consuming the “used” air that was pulled down the flue. When both the water heater and furnace are off, there’s no problem. Well, except for the fact that there is cold air dropping down the flue, causing the flue pipe to get abnormally cold.

When the water heater fires up, instead of the exhaust gasses going up the flue, they hit the cold air standing in the flue pipe and then spill out of the draft diverter into the basement or utility room. Because the flue pipe is cold, the water heater can not warm it up enough to establish a positive draft. Even when the drier stops running, the flue pipe may be cold enough to prevent normal flue operation for a long period of time. (This problem is also shows up when the flue is in a masonry chimney on an outside wall and the flue liner has been grossly over sized.)

The situation gets worse when the furnace comes on. When the burners first start the draft inducer will begin moving air. Since the flue pipe is ice cold, very little air initially gets up the flue. Instead, the air is pushed out the draft diverter of the water heater.

When the furnace burner ignites (usually around 15 seconds after the draft inducer started) the warm exhaust gasses eventually begin to warm the flue. This process could take anywhere from a few minutes to a few hours. During this time, the “used” air that’s dropping out of the water heater draft diverter is filling the space around the water heater and furnace. If it is a confined space, the furnace will begin to consume the “stale” air (re-burn) and that’s when carbon monoxide is produced. 

Instead of seeing 10ppm or less in the flue gasses, it may jump to 100 or 400ppm. This cycle will continue until the flue is warm enough to begin drafting properly. In the mean time the area around the furnace and water heater is filling up with CO laden air at a faster and faster rate.

This may sound like an unlikely scenario but I’ve seen it occur frequently on two story homes where the flue is routed near a garage or outside wall and the flue pipe is running thru an ice cold attic. When this happens the furnace will be running and the top of the water heater will be warm or down right hot to the touch even though the water heater is off. This problem is aggravated when the water heater connector is not sized properly or not connected correctly to the flue tee.  Read the rest …