Carbon monoxide leak from steam boiler

Mgl

I have a 1960s Peerless boiler that has been working fine for me so far this winter (and the last 6 years I have lived in this house).  It does not use any water and has given me no issues. 

I just had somebody from a local HVAC company (that does a lot of steam heat repairs and installs) do an annual checkup on the boiler and he found carbon monoxide levels of 14ppm when he put his meter next to the hole at the top of the boiler jacket where the steam pipe goes in.  The measurement in the flue pipe was around 50ppm (which he said was fine).  My understanding is 14ppm is similar to what a gas stove burner puts off and slightly above the level of 9ppm which is the acceptable level to have in your house.  I highly doubt the sustained level in the boiler room is above 9ppm.  My co detector reads above 30 ppm and shows nothing.  Is this something I should be concerned about and reason enough to replace the boiler (which was the HVAC tech's recommendation)?

Jamie Hall

First off, there really is no safe level for long duration carbon monoxide exposure.

Second, and much more concerning, there shouldn't be any flue gas leakage from the boiler. I would very much want to take all the jackets (and any insulation) off that boiler and see if I could determine where the flue gas leak is coming from. It might be simply a deteriorated gasket, but... it might not be.

EdTheHeaterMan

Anything under 100 PPM Carbon-monoxide (CO) in the flue gas, that is leaving an oil or gas fired heating appliance that is exhausted up the chimney (or outdoors via any vent) is considered normal and you have nothing to worry about. The fact that the probe was not in the vent pipe and just near the boiler at an opening that a steam pipe is connected to, leaves me to believe that the boiler is more than 15 years old, the sealant between the boiler sections and the gaskets or sealant that connects the cast iron to the base where the fire is happening may have some leaks. That can be easily taken care of with high temperature sealants. That said, Steam boilers are mainly Category I vent appliances, meaning that the pressure inside the flue is lower than the pressure in the room the appliance is located. (leaks should suck basement air into the heater, not the other way around).


Has the technician actually checked the chimney for a proper draft? It is quite possible that the CO condition the tech talked about only happens for the first minute or so during start up. Once the chimney warms up. The chimney will draft properly and any byproducts of combustion will be inhaled by the chimney vent pipe and any leaks in the boiler that showed the CO leak you mentioned.


Since I can not say with certainty that you do not have a problem, I will recommend that you have a qualified chimney expert inspect your chimney for proper draft and that the lining is adequate for safe operation. After that, have that combustion test completed again after the appliance has been operational for at least 5 minutes. Not on start-up

EDIT: and What @Jamie Hall said.

bburd

Even if the fire side of the boiler is not completely sealed, which is not unusual, that's a conventional boiler so the chimney / exhaust vent draft should put it under negative pressure when it's operating. Sounds like the venting system needs to be checked.

Mad Dog_2

Alot of times the furnace cement cracks and spells away around the draft hood and flue collector.  Pull top of jacket off and go to town with some fresh Furnace cement generously applied on a 45 degree angle from the Top of Cast Iron to the side of the collector hood.  Mad Dog 🐕 

EdTheHeaterMan

Mad Dog_2 said:

Alot of times the furnace cement cracks and spells away around the draft hood and flue collector.  Pull top of jacket off and go to town with some fresh Furnace cement generously applied on a 45 degree angle from the Top of Cast Iron to the side of the collector hood.  Mad Dog 🐕 

Or you could just try sealing it of a 22.5° angle.

pedmec

Yes, i would be concerned because that means you have carbon monoxide leaking most likely from the flue collector box on top. If that is the case it can only get worse if not addressed. 50 ppm in the flue is fine but you cannot guarantee that you will always be at that level. too many variables can happen to cause that CO to spike. have it located and repaired. A combustion analyst is always about safety first. unlike a stove you wont know your boiler might be burning incorrectly.

Mgl

Thanks everybody for the advice.  This was all very helpful.

Mad Dog_2

Ed..on Second thought...11 1/4  degrees is ideal!  (Heating humor). Mad Dog 🐕 

EBEBRATT-Ed

@Mgl

This is my take. Since your C0 of 50 in the flue pipe is ok for a boiler that age I would suspect a sealing issue as others have mentioned. If your CO was over 100 that would indicate a burner or poor combustion issue. You don't seem to have that. Probably just some flue gas leaking. Good that your technician checked he was doing his job but should dig a little deeper.

EdTheHeaterMan

Mad Dog_2 said:

Ed..on Second thought...11 1/4  degrees is ideal!  (Heating humor). Mad Dog 🐕 

I would stay away from anything less than 20... The closer you get to flat, the more likely it will be too thin for snow boarding.