Housing...Inside and Out

January 1, 1999
Carbon Monoxide

Carbon monoxide is an odorless, colorless gas that can be fatal when breathed. It is sometimes difficult to determine if carbon monoxide is the culprit, because its symptoms are similar to flu and allergies. Low levels can cause nausea, dizziness, weakness and muscle ache. Higher doses can impair judgement, cause paralysis or coma and death.

A buildup of carbon monoxide can occur several ways: 

  • when flues or chimneys become blocked so exhaust cannot be vented to the outside;
  • when a fuel burning furnace has a cracked or rusted heat exchanger, allowing combustion gases into the living spaces;
  • when fuel-burning space heaters, ovens, ranges or grills are operated in the home without adequate ventilation; 
  • when car exhaust from an attached garage enters the home;
  • when combustion equipment is not working properly and causes incomplete combustion; 
  • when there is a negative pressure balance between the inside and outside of the home, preventing adequate venting of combustion gases.

There are carbon monoxide detectors you can install, which will alert you to dangerous levels of carbon monoxide. It is important to choose and place a detector wisely and maintain it to assure accurate sensing of carbon monoxide.

If you feel bad only when you are inside the home and the symptoms gradually disappear after you have left, or if more than one person in the home has similar symptoms, then you may have a problem with carbon monoxide. Remember carbon monoxide related symptoms are similar to those of the flu.

Reduce the risk of carbon monoxide by keeping all combustion equipment well maintained and inspected for safety. It is advisable to have your combustion heating systems inspected by a trained professional every year. Such inspections should include checking for:

  • blocked openings to flues and chimneys 
  • cracked or disconnected flue pipe 
  • signs of soot around openings in your furnace 
  • rust or cracks in the heat exchanger 
  • soot or creosote build-up
  • exhaust or gas odors

Always operate combustion equipment for its intended purpose and make sure it has been installed correctly. Never use unvented combustion appliances indoors.


Written by Dr. Francis Graham (Retired)

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