Un-vented indoor heating appliances is sizable source of indoor pollution. As described from "The Condensed Chemical Dictionary" carbon monoxide is a colorless gas or liquid; practically odorless, also classed as an inorganic compound. These specific attributes make carbon monoxide unable to sense by humans.

What is Carbon Monoxide?
What are the sources of Carbon Monoxide?
Health Effects
Reduce Exposure



Sources of Indoor Air Pollution

Definition (from The Condensed Chemical Dictionary):

Colorless gas or liquid; practically odorless.  Burns with a violet flame.  Slightly soluble in water; soluble in alcohol and benzene.  Specific gravity 0.96716;  boiling point -190oC; solidification point -207oC; specific volume 13.8 cu. ft./lb. (70oF).  Auto-ignition temperature (liquid) 1128oF.  Classed as an inorganic compound.

Sources of Carbon Monoxide

Un-vented kerosene and gas space heaters; leaking chimneys and furnaces; back-drafting from furnaces, gas water heaters, wood stoves, and fireplaces; gas stoves. Automobile exhaust from attached garages. Environmental tobacco smoke.

Health Effects Associated with Carbon Monoxide

At low concentrations, fatigue in healthy people and chest pain in people with heart disease. At higher concentrations, impaired vision and coordination; headaches; dizziness; confusion; nausea. Can cause flu-like symptoms that clear up after leaving home. Fatal at very high concentrations.

Levels in Homes

Average levels in homes without gas stoves vary from 0.5 to 5 parts per million (ppm). Levels near properly adjusted gas stoves are often 5 to 15 ppm and those near poorly adjusted stoves may be 30 ppm or higher.

Steps to Reduce Exposure to Carbon Monoxide

  • Keep gas appliances properly adjusted.
  • Consider purchasing a vented space heater when replacing an un-vented one.
  • Use proper fuel in kerosene space heaters.
  • Install and use an exhaust fan vented to outdoors over gas stoves.
  • Open flues when fireplaces are in use.
  • Choose properly sized wood stoves that are certified to meet EPA emission standards. Make certain that doors on all wood stoves fit tightly.
  • Have a trained professional inspect, clean, and tune-up central heating system (furnaces, flues, and chimneys) annually. Repair any leaks promptly.
  • Do not idle the car inside garage.

Environmental Protection Agency
Last updated on Monday, November 18th, 2002


The information provided on this page is based upon the EPA current scientific and technical understanding of the issues presented. Following the advice given will not necessarily provide complete protection in all situations or against all health hazards that may be caused by indoor air pollution and other indoor environmental contaminants.  The EPA have not reviewed or approved all the information and documents on indoor air quality that may be provided by other groups or organizations.


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