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CARBON MONOXIDECarbon monoxide is a tasteless and odorless gas that is life threatening. Carbon monoxide is just slightly heavier than air. Carbon monoxide is a result of incomplete combustion. The result of complete combustion is carbon dioxide. There have been discussions about cracked heat exchangers in furnaces and carbon monoxide. Although a cracked heat exchanger can result in carbon monoxide in the home or business it requires a fairly large crack or hole for this to happen. A more serious concern is a plugged or restricted flue or lack of combustion air. A plugged or restricted flue will not allow the combustion products which mostly consist of carbon dioxide and water in the form of steam to vent up and out of the house. Since the products of combustion can not be vented out of the house they spill out of a draft hood for either the water heater or the furnace or both. Instead of having air or oxygen to burn now there is a significant amount of carbon dioxide. When carbon dioxide is burned instead of oxygen, the result is huge amounts of carbon monoxide which now spill out of the draft hood or hoods and into the home. This is the reason that it is important to have a flue or chimney cap that prevents birds, and other animals from plugging or restricting the vent system. Combustion air can also be a serious problem. It takes 10 cubic feet of air to burn one cubic foot of natural gas under ideal conditions. Most furnaces require approximately 15 cubic feet of air to burn one cubic foot of gas. A 100,000 BTU per hour furnace requires 1500 cubic feet of air per hour or 25 cubic feet per minute (CFM) while it is running. Tight home construction and old homes that have new windows and other repairs to reduce the costs of heating and air conditioning can also be a problem. The clothes dryer exhausts approximately 150 to 250 CFM and then there are exhaust fans for the kitchen and bathroom. These appliances remove air from the home and air comes back in through holes or cracks in the house. If the only hole in the house is the flue vent, the air comes down through the flue vent and does not allow the products of combustion to vent up and out of the house. Again the products of combustion spill out of a draft hood for the furnace or water heater with the same results as a plugged or restricted flue. Return air grills located in the furnace room or furnace area can also cause negative pressure which, results in a down draft in the flue venting system. This will also cause the products of combustion to spill out of a draft hood for the furnace or water heater.
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