Carbon Monoxide and older boiler

BenS

Hello-

First time poster here, but I have read Dan's "We Got Steam Heat!" book.

We have an ~40 year old boiler (manufactured in 1983) that we recently needed serviced to replace a broken sight glass. We hired a contractor to come and replace it and they're encouraging us to do larger maintenance tear-down effort or replacement of the boiler due to high CO detection. I'm trying to figure out how severe the issue is.

I understand that CO is a risk and we have what I believe is a good CO/gas detector mounted in the room where the boiler is located. (https://www.kidde.com/home-safety/en/us/products/fire-safety/co-alarms/kn-coeg-3/) It is mounted across a doorway, about 4' away from where the boiler is located, at about 6' high (which is ~3' above the boiler). It has a digital readout that keeps track of levels, and has recorded a peak of 74 PPM. When the boiler first kicks on, it will register a brief spike, but most of the time the boiler is firing, however, it reads 0.

The technician who replaced the sight glass placed a probe directly around the pressure release valve on top of the boiler and detected around 200 PPM. Is this unusually high at that location? We have generally good airflow in this room since it has doorways on 3 sides without doors, and we keep a window cracked in a neighboring room to ensure there's airflow for combustion. Should I be replacing this boiler? We're past heating season, so I have time to get quotes from several contractors, but I also want to make sure that this concern isn't overblown.

Thanks for your help!
Ben

EdTheHeaterMan

Gas boiler of Oil fired?

If there is a buildup of carbon or other foreign material on the burners or heat exchanger surfaces, then something called impingement can happen. This means the actual flame that is well over 1500°F touches or wipes against a solid surface that can not possibly achieve that temperature (like cast iron with water on the opposite side of the flame) causing the flame temperature to drastically drop, resulting in incomplete combustion. This can be a major source of carbon monoxide. You see, the byproducts of combustion of a hydrocarbon fuel and the oxygen in the air include Carbon Dioxide when the combustion is complete. Incomplete combustion can result in unburned free carbon (Soot) or Carbon Monoxide (only one oxygen atom in the molecule in stead of the preferred 2 oxygen atoms) resulting from the flame.

Now, as long as all the CO2, CO, free Carbon, Oxygen from excess air, Nitrogen and all the other trace gasses go up the chimney, then you need not worry. But on start up of any flame, there is a rapid expansion of gasses, part of the rapid expansion (or eeny, weeny, mini explosion) makes the byproducts of combustion expand in all directions... out the air intake, up the chimney, thru the draft hood, anywhere it can go, in any direction. What we count on is the chimney draft is greater than all the other forces and cause a line of least resistance to vent those byproducts thru the heat exchanger, past the draft diverter (or barometric on an oil burner) and go out of the home up the chimney. As those gasses leave, the excess heat not absorbed by the heat exchanger (Stack Temperature) increases the chimney draft and eventually all the gasses along with extra dilution air from the boiler room, will flow up the chimney because the greater heat makes those gasses more buoyant than the surrounding atmospheric air pressure acting on the boiler and chimney. "See illustration from Field Control reference guide"



Understanding this concept will allow (help) you to understand the CO meter readings

In a gas burning appliance with atmospheric burner and Category I venting system (chimney)

1. On start up complete and incomplete combustion happens instantly causing high (200 PPM) reading close to the equipment.
2. This puff of combustion byproducts reaches the CO meter at the opposite wall after being diluted with ambient room air (70 PPM)
3. Chimney becomes more efficient in removing byproducts of combustion in less than 30 seconds.
4. This improves combustion efficiency and also removes ambient air from the boiler room up and out the chimney.
5. Both CO meters register lower readings gradually until the readings reach safe levels within a very short time (less than 3 minutes)

This is normal. A manufacturer may however, be able yo reduct the start up "Puff" with the use of a slow opening gas valve or a step gas valve. You can also get the CO to be lower on start up if there is unusual corrosion, carbon or other foreign debris on the burner or heat exchanger, by removing this build up and cleaning the burners and HX to "Like New" condition.

jringel

if this is a 40-year-old cast iron boiler you may be getting leakage through the boiler seals or breech hood (which is very close to where he was testing) until the chimney comes up to speed. This will show increased CO close to the unit on start up. You can test it by taking combustion readings in the flue and overfire and comparing them. if the co2 is lower or the o2 is higher in the flue you have air leakage into the unit. If its an oil system I would also recommend a pre-purge control to help get the gases moving in the right direction prior top light off. with that being said at 40 years old the unit has exceeded its design life and with fuel prices climbing you may want to consider replacement.

pecmsg

Get a LOW Level CO detector such as the Defender. 

The Kiddie will alarm after 70 PPM has been maintained for up to 3 hours. Dangerous levels. A low level will alert at 15 PPM.  

BenS

Thanks for your responses! Our boiler is natural gas, not heating oil. We're in Denver, Colorado. (I should have mentioned that up front.)

I'm certain that with a 40 year old boiler, it's not running as efficiently as it was when it was new, so my wife and I have been discussing replacing the boiler, but it is not an expense we'd planned for this year. The contractor also pointed out that our existing unit doesn't have a redundant pressuretrol with a manual reset. Aside from this issue with the sight glass leaking/breaking, the boiler has overall been operating fairly well in the 18 months since we moved in.

Ed, just to make sure I understand, you'd expect that it would level out/drop off once the draft is working optimally and that should happen within 30s or so? I'd like to understand what to expect should we go ahead with the replacement to evaluate that everything's working as expected.

Besides a wholesale replacement, the company also offers a teardown/cleaning that seems like it is meant to address impingement, but given the age of the unit, it doesn't seem worth that level of effort. Thanks!

mattmia2

If it is steam and it isn't leaking, a new boiler won't be much if any more efficient assuming the old one is installed properly and certainly not enough to make the difference between cleaning and adjusting the current one vs replacement.

Isn't @Mark Eatherton out that way?

captainco

That is a dumb place to test!! The CO test should be in the flue. Most alarms must be exposed to CO for at least 30 seconds before reading a number. If the contractor was using a personal CO monitor they are heat sensitive and respond when nothing is there. Must use a combustion analyzer, and if they have one they need to learn how to use it.

Yes, this is Mark Eatherton home town.

ch4man

since everyones assuming what happened in your basement when the technician was there ill do the same and assume too.

if the boiler was up and running when he tested for CO by the relief (not right at burner light off) and he was using a proper analyzer, I would assume its leaking flue gasses through failed retort between the sections.

if so you need a new boiler, no assumption there

captainco

If CO is leaking into a room it will initially be diluted more than 100 to 1. Or if the boiler is making 200 ppm internally, when measured externally it would measure only 2 ppm. If the alarm had a reading of 74 ppm then there was a whole lot more CO being made then just 200 ppm momentarily, Yes there is a spike at light-off but that would not be enough to cause an alarm to read 74 ppm.

Dave Carpentier

Afaik, consumer-grade CO detectors are surprisingly slow to respond and have a limited life-span of maybe 10 years before they shouldnt be trusted. Some brands (maybe all, nowadays ?) will let you know when it needs to be replaced. I always write the date on mine, just to be safe.
You might be able to find somewhere to rent a proper calibrated confined space monitor that you could use for a few cycles to see whats happening in the room air.
Is there proper outside make-up air coming into the room ?

EBEBRATT-Ed

Just because a boiler is making Co does not mean an automatic replacement. The burners & boiler should be cleaned thoroughly and the sealing between the boiler sections checked. Then combustion checked along with checking gas pressure and flue draft.


I would like someone to tell me why "old boilers" make Co and new boilers are ok. What is it that can't be fixed to stop the Co?

JakeCK

My 40 year old Weil McClain runs at %80+ and produces no co. Age has little to do with it.

Bob Harper

Proper sequential combustion analysis is your key. As for that UL listed CO alarm, understand its limitations. Listed CO alarms are merely death alarms- get out before you die. They do not protect against CO poisoning. Their alert levels are based upon 10%COHb, which is the medical definition of CO poisoning for smokers. Your 74 ppm may have been a false positive. I had that same alarm many years ago before I took Jim's NCI course. I could always tell when my used hairspray because it would peak at 200-600 ppm and holler. You need to take sequential samples to map the trend: steady, rising or falling CO and O2, draft, stack temp, and O2 at floor. Lot's of potential causes and yes, equipment and venting can and do change over time, which is why you must test annually.

SeanBeans

Hey @benS !

I work for a plumbing and heating company based in Lakewood. I have a bunch of happy customers with steam systems in denver and would love to assist you in replacement/repair/service or anything you could possibly need with your steam system. Let me know! 

EdTheHeaterMan

SeanBeans said:

Hey @benS !

I work for a plumbing and heating company based in Lakewood. I have a bunch of happy customers with steam systems in denver and would love to assist you in replacement/repair/service or anything you could possibly need with your steam system. Let me know! 

@SeanBeans... this is great but to be sure @BenS has a better chance of seeing this, you should send him a message. That may trigger an email that he might see before coming back to HH

SeanBeans

EdTheHeaterMan said:

Hey @benS !

I work for a plumbing and heating company based in Lakewood. I have a bunch of happy customers with steam systems in denver and would love to assist you in replacement/repair/service or anything you could possibly need with your steam system. Let me know! 

@SeanBeans... this is great but to be sure @BenS has a better chance of seeing this, you should send him a message. That may trigger an email that he might see before coming back to HH

Good idea! Message sent 

Hap_Hazzard

BenS said:

Thanks for your responses! Our boiler is natural gas, not heating oil. We're in Denver, Colorado. (I should have mentioned that up front.)

I'm certain that with a 40 year old boiler, it's not running as efficiently as it was when it was new, so my wife and I have been discussing replacing the boiler, but it is not an expense we'd planned for this year.

Don't be so sure. I have a 40 year old boiler, and last time I had the stack gases analyzed, by a professional technician, the CO was ZERO! Not that there wasn't some CO in the exhaust, but it was below the level that the analyzer could measure, and he was using an analyzer I couldn't even afford.

So my advice is to get you exhaust gases analyzed by a professional—preferably someone listed on this site or someone from the gas company, that is to say, someone who doesn't have a vested interest in selling you a new boiler.

Personally, my BS detector would be flashing red the minute someone recommended replacing my BOILER because of a problem with the stack gas composition. That's a BURNER issue. You can completely replace your burner assembly if necessary and keep your old boiler as long as it's in decent shape, but even that would be a drastic solution. Burners can be tuned and replaced as necessary without replacing the whole burner tray. Individual manifold spuds can be replaced without replacing the whole manifold, and the manifold can be replaced independently of the gas valve, but probably all you need is an adjustment by a professional gas man.

When I had mine tested, I had just finished adjusting them, following the instructions in the Installation and Operation Manual (IOM) that came with the boiler, and the technician said it was perfect. DON'T DO THIS! I am not recommending adjusting your own burners, but do read the manual so you understand how the burners work. Based on what I have learned since then, I now understand that I was just lucky. Without even having a gas analyzer, and having no experience adjusting burners, things could have very easily gone horribly wrong, so, again, have a professional do this.