Myth #8 - CO is only caused by incomplete fuel combustion. (Wrong!)

Well, technically I guess Myth #8 is "correct", sort of.

It's really like arguing about whether you got 12 or 14 inches of rain. If there's a foot of water in your basement, what difference does it make?

Here's a scoop for you.

While there is NO such thing as perfect combustion, natural and LP gas come pretty close.

Gas furnaces and gas stoves run for decades without building up much soot or ash. Their products of combustion might include some unsavory gasses, but that's NOTHING compared to what comes out of your vehicle's exhaust pipe, or some factory chimneys.

Gas burner flame
Natural Gas Burns Clean

For the sake of argument, let's examine an atmospheric vent gas furnace.

Atmospheric vent means the furnace depends on warm air to rise and carry the products of combustion through the flue and out of the house. There's no powered draft inducer to push or pull air through the heat exchanger. In the vernacular they call this a "positive draft in the flue".

If you misadjust the flame on the gas burners by closing down the primary air shutters, you'll see an increase in carbon monoxide in the flue. If you crank the gas pressure to the burners way up, you'll over fire the furnace and see a little more CO in the flue gasses. At any stage along the way you can say that the CO was caused by "incomplete" combustion. But, because the CO levels are relatively low (still under 400ppm) and they are being carried out of the structure by the flue, there is NO immediate reason for alarm. Putting it another way, incomplete combustion does not necessarily lead to CO poisoning or CO health problems.

Now, with a perfectly adjusted furnace (with 0ppm CO output) there is almost complete combustion. But, if a roofer rests a stack of shingles on your flue cap (on the roof) and crushes it, guess what! (Same situation if the bird screen on the flue cap is clogged with cotton wood, or birds build a nest in an open flue cap during the summer.) You're well adjusted furnace will soon start producing very high levels of carbon monoxide because the flue is blocked. Given some time, the CO will migrate into the home and that's when real problems can occur.

Is it the furnace's fault? Nope! Is there "incomplete" combus-tion? Yep! Did the "incomplete combustion" cause the problem?