Carbon monoxide is an odorless, colorless, tasteless gas.  It is created to some degree when anything burns.  Since CO has no effect on the senses, you could be standing in a room full of it and not know it.  If the concentration of CO is high, you’ll start to get a headache, might get nauseous, will eventually fall unconscious and could possibly die. 

This video, produced by CNN is short, but does a good job of explaining carbon monoxide poisoning and why it is so deadly.

Main Causes of Carbon Monoxide Poisoning

Liquid fueled engines are the Number 1 cause of CO poisoning.

This includes automobiles running in garages, generators running inside of homes or too close to open windows of a home, gas-operated power equipment (power sprayers, big floor sanders, big concrete finishers, weed whips, chain saws, etc.)

The engines produce an enormous amount of carbon monoxide in a short period of time.  Even if you’ve shut the engine off, the CO lingers in the area and if the area is not well ventilated and you stay in that area, you can be overcome by CO without noticing it.

Broken, blocked, and mis-routed gas appliance flues are the Number 2 cause.

Heating-cooling contractors make a big deal about gas furnace checks, and say you should have your furnace heat exchanger (and the whole system) checked annually.  But the most frequent cause of problems with carbon monoxide and gas furnaces and gas water heaters are flue and combustion air issues.  The flue should be critically checked every season, right along with the furnace.

Flue draw, capacity checks and size confirmations are not done all the time.  Technicians walk past the flue, pay no attention to the amount of available combustion air, and go straight for the heat exchanger check.  Once they are satisfied that the heat exchanger is OK, they finish the clean and check and only give a cursory glance at how the flue is routed, how much draft it produces and how much free area is available to support combustion appliances.

Heat exchanger cracks, villainized by contractors and the media as the prime source for CO poisoning, are rarely the real culprit.  Problems with gas appliance flues and limited combustion air are the true causes of carbon monoxide poisoning in residential applications.

Heat exchanger cracks

Heat exchanger cracks can be dangerous, but, in residential applications, they rarely cause carbon monoxide poisoning.  Heat exchanger cracks will cause issues with flame roll out, burnt wiring, and may produce CO that pools in front of the furnace and around the water heater.

This video shows what happens when a heat exchanger has large cracks or holes.

Next:  Myth-1 – Heat Exchanger Cracks Cause CO