CO levels at start-up

Servicewiz_3

Through the years , I have noticed that when I am working on natural gas fired

Equipment , that I have a brief time of high CO during lightoff & between HI & Low

fire. This CO level , almost always comes back , well below a proper level ( 100 PPM)

in the flue gas. Just curious , what may be the cause?

Thanks in advance for any insight!!

J. Scheel Jr.

pedmec

What category of appliance? it makes a difference.

Servicewiz_3

Just today , Category I. Why does the Category make any difference?

pedmec

Because CO doesn't really change on start up with a cat 4 unless you adjust the gas valve. its pretty solid from ignition to shutdown thanks to prepurge and the premix burner.

A category 1 will always produce high CO on start up because it has a bad fuel/air ratio mix on start up. There is a lot of unburnt fuel not mixed with the air on start. Step opening gas valves have helped but only so much you can do with a cat 1

mattmia2

i believe the answer is that you don't get proper draft until the appliance is somewhat hot so the burner is starved for air at startup.

mattmia2

this makes the ameritherm seem like an even worse idea.

EBEBRATT-Ed

When you put a pan of cold water on a gas stove to boil it it makes CO because the hot flame is being chilled by the cold pan. The CO goes away as the water warms up.

Same thing with a furnace or boiler. Until the HX warms up you will make CO

Steamhead

https://forum.heatinghelp.com/discussion/comment/1891933#Comment_1891933

Only if the flame is so high it contacts the cold metal.