Combustion Byproducts

Carbon Monoxide (CO)

Carbon monoxide is a colorless, odorless, and tasteless gas. Carbon monoxide can reach levels high enough to kill without you being aware of its presence. At lower levels of exposure, it can cause symptoms that are often mistaken for the flu, including headaches, nausea, dizziness, fatigue, and disorientation. The effects of CO exposure can vary greatly from person to person depending on age, overall health and the concentration and length of exposure.


Unvented kerosene and gas space heaters; leaking chimneys and furnaces; back-drafting from furnaces, gas water heaters, wood stoves, and fireplaces; gas stoves, generators and other gasoline powered equipment; automobile exhaust from attached garages; and tobacco smoke. Incomplete oxidation during combustion in gas ranges and unvented gas or kerosene heaters may cause high concentrations of CO in indoor air.

Worn or poorly adjusted and maintained combustion devices (e.g., boilers, furnaces) can be significant sources, or if the flue is improperly sized, blocked, disconnected, or is leaking. Auto, truck, or bus exhaust from attached garages, nearby roads, or parking areas can also be a source.

Minimizing Risk of Carbon Monoxide Exposure

  • A carbon-monoxide detector. They can help alert you to increased levels of carbon monoxide in your home, but they are not foolproof.
  • The Consumer Product Safety Commission recommends installing at least one CO detector per house, near the sleeping area.
  • Homes with several sleeping areas require multiple detectors. For added protection, locate additional detectors at least 15 feet from the furnace.
  • Look for detectors with the UL (Underwriters Laboratories) seal, and which feature an audible
  • alarm. Alarms can purchased at home supply stores for around $30 or less.
  • Have furnaces and fireplaces inspected for cracks, gaps, rust, corrosion or debris by a qualified professional before each heating season.
  • Fireplace chimneys and flues should also be checked and cleaned every year.
  • Have gas appliances serviced yearly by a qualified service technician.
  • Stove burners should be cleaned and adjusted to minimize the amount of carbon monoxide produced.
  • Gas dryer vents should be checked for lint buildup that may restrict ventilation.
  • Use non-electrical space heaters only in well-ventilated areas.
  • Never start or leave cars, trucks or other vehicles running in an enclosed area. Never leave the motor running in a vehicle parked in a closed garage.
  • Never operate barbecue grills indoors or use stove tops or ovens that operate on flammable fuels to heat a residence.
  • If living in a multi-family dwelling, be aware that carbon monoxide can enter your residence through floor boards, cracks or underneath doors.
  • Never run a generator, pressure washer, or any gasoline-powered engine inside a basement, garage, or other enclosed structure, even if the doors or windows are open, unless the equipment is professionally installed and vented.

Carbon Dioxide (CO2)

At room temperature, carbon dioxide is a colorless, odorless, faintly acidic-tasting, non-flammable gas. In its solid form, CO2 is called dry ice. Carbon dioxide is a normal byproduct of breathing. CO2 is also produced in the burning of fossil fuels and decaying vegetation. Carbon dioxide can accumulate in buildings that house a lot of people or animals, and is a symptom of problems with fresh air circulation in the building or home. The amount of carbon dioxide in a building is usually related to how much fresh air is being brought into the building. In general, high CO2 levels (above 1,000 ppm) indicate a potential problem with heating, ventilation, and air conditioning (HVAC) systems.