Where to Look For Problem Sources of Carbon Monoxide in the Home
A forced air furnace is frequently the source of leaks and should be carefully inspected. Measure the concentration of carbon monoxide in the flue gases. Check furnace connections to flue pipes and venting systems to the outside of the home for signs of corrosion, rust, gaps, holes. Check furnace filters and filtering systems for dirt, blockage. Check forced air fans for proper installation and to assure correct air flow of flue gases. Improper furnace blower installation can result in carbon monoxide build-up because toxic gas is blown into rather than out of the house. Check the combustion chamber and internal heat exchanger for cracks holes, metal fatigue or corrosion -- be sure they are clean and free of debris. Check burners and ignition system. A flame that is mostly yellow in color in natural gas fired furnaces is often a sign that the fuel is not burning completely and higher levels of carbon monoxide are being released. Oil furnaces with similar problems can give off an "oily" odor. Remember you can't smell carbon monoxide.
Check all venting systems to the outside including flues and chimneys for cracks corrosion, holes, debris, blockages. Animals and birds can build nests in chimneys, preventing gases from escaping.
Check all other appliances in the home that use flammable fuels such as natural gas, oil, propane, wood or kerosene. Appliances include water heaters, clothes dryers; kitchen ranges, ovens or cooktops; wood-burning stoves, gas refrigerators. Pilot lights can be a source of carbon monoxide, because the by-products of combustion are released inside the home rather than vented outside. Be sure space heaters are vented properly. Unvented space heaters that use a flammable fuel such as kerosene can release carbon monoxide into the home. Barbecue grills should never be operated indoors under any circumstances, nor should stove tops or ovens that operate on flammable fuels be used to heat a residence. Check fireplaces for closed, blocked or bent flues, soot and debris.
Check the clothes dryer vent opening outside the house for lint. If initial testing does not confirm the presence of carbon monoxide, there may be several reasons:
Testing equipment used to measure the presence of carbon monoxide in the air must be calibrated to sense low levels of gas concentration. Some detection devices only measure concentrations of 1,000 parts per million and higher, significantly above safe levels. Testing equipment should be capable of sensing levels as low as 15 parts per million. For example Underwriters Laboratories' standards for residential carbon monoxide detectors require that they alarm when carbon monoxide reaches 100 parts per million for a 90 minute period. If initial readings don't reveal sufficient concentrations of carbon monoxide to set off the alarm, testing equipment which registers levels over a 24-hour period should be used to help identify the source.
If doors or windows have been left open or appliances turned off, and outside air enters the home, carbon monoxide can dissipate. This would create a lower reading than the level that triggered the alarm. To help assure proper measurement after evacuating the home, carbon monoxide readings should be conducted immediately and no later than a few hours after the alarm has sounded. Leave doors and windows shut after evacuating.
If appliances flues and chimneys are confirmed to be in good working order, the source of carbon monoxide leaks may be from backdrafting. This condition exists primarily in newer more energy efficient, "airtight" homes. Flue gases normally vent to the outside through flues and chimneys. As temperatures drop at night, air pressure inside an airtight home may become lower than outside, causing flue gases that normally exit the house to turn around and flow back down the pipes. Inadequate air supply in a room where two or more combustion-driven appliances share the same air source, such as a water heater and furnace in a utility closet, can create a more complicated form of backdrafting called reverse stacking. This occurs when one appliance turns on, such as the furnace, and is unable to get adequate fresh air. So when the furnace operates, it then draws contaminated air from the water heater exhaust, and spreads polluted air throughout the house.
A sticking thermostat can keep the furnace running continually, depleting the oxygen supply inside the house. This can lead to backdrafting.
In multiple family dwellings where living spaces share walls and pipes, carbon monoxide from one unit may go into a neighboring space through floor boards, cracks, or underneath doors.
If a home has an attached garage, carbon monoxide produced by the car exhaust can leak into the house. This is especially a problem for persons who may run the car engine frequently for periods of time even if the garage door is left open.