Combustion Analysis Question

Sweet_Lew

Hey All,

Hoping this is the correct place to post this. Just had a new heating company come out for a routine cleaning on our boiler (18 year Bryant\Dunkirk). He performed a combustion analysis (first time any one has done that). The readings were horrible (per the tech):

O2 - 12.8%
CO - 2156 ppm
Eff - 83.8%
CO2 - 4.6%
T-Stk - 183 F
T-Air - 62.7 F
EA - 138.8 %
CO (()) - 5557 ppm

He stated it was due to a cracked heat exchanger and shut off the gas to the boiler along with the boiler itself deeming it unsafe and a new boiler was needed. Can someone help me understand these readings? He explained the CO readings were waaaay over the recommended amount, I just want to understand the other readings.

Thanks,

Lew

mattmia2

Is the boiler set up for hot water or steam? If it is hot water, if the hx is cracked there will be water all over the floor leaking out of the system and on to the floor. If it is steam, maybe but unlikely. Much more likely is it needs to be cleaned and tuned properly.

Sweet_Lew

It's hot water. That was my thought too. If the exchanger was cracked, shouldn't it be leaking water? I'm curious of the boiler is just running rich.

unclejohn

This is a hi eff. boiler correct? Do you have a model #. Here is info for CO 4.3-6.3% and CO2 8.2-9.3% for model DCCF/DCBF. Have not seen CO2 numbers above 120 ppm for any boiler, the chart I found did not list the max CO2. I wonder why he did not make any adjustments? The meter is also only as good as the tech. holding it. It has been mentioned before that sometimes we all make mistakes like leaving your meter on oil when your doing a gas test.

unclejohn

Q90 series info.
5. Insert the sample probe of your combustion analyzer into the hole you drilled in step 2
above, about halfway into the exhaust gas stream. Take a flue gas reading and observe
the CO2
value. Adjust the throttle screw until the CO2
value is between 8.5 and 10%.
(O2
between 5.5% and 2%) Turning the throttle screw counterclockwise increases the
rate and the CO2
value. Turning the throttle screw clockwise decreases the rate and
the CO2
value. Allow the appliance to stabilize for approximately 1 minute after adjusting the throttle screw before you take a reading with your combustion analyzer.

icy78

Ouch!
Certainly a dangerous situation. Over 400ppm its redtagged.
I would shut it down.

Having said that...I don't think he knows what he's doing. Might just be using the CA as a scare tool, but doesnt know how to interpret it.
 So, assuming he took readings in the correct location....
It looks fixable.
Certainly underfired.
Maybe dirty or damaged or misaligned parts.
What was the draft reading?
Where did he take his readings?
Were those numbers he showed you steady, or rising? 
How long was the probe in...1 minute? 10min? 20min?
Take a few pics, of the whole boiler room, esp the boiler and flue, and post them.
Take a pic of the outside too, as in chimney termination.

STEVEusaPA

The CO is very dangerous. What other things did he do. I'd have him check gas pressure, check burner alignment, and draft.
Looks like it might be underfired for starters.
Selecting the wrong fuel won't affect CO or stack temp numbers.

Big Ed_4

Did he perform any work to correct the bad readings ?

Sweet_Lew

Thank you all for the replies. The boiler is not high efficiency. It's rated at 84% efficiency. He supposedly cleaned the boiler before running the analysis. No work performed after the analysis other than calling me to tell me I needed a new boiler as the readings equated to a cracked heat exchanger. I am having two other companies come out for second opinions. I can get pics up later. Thanks again!

Alan (California Radiant) Forbes

There are many ways to clean a boiler. You can clean the firebox and the burners, but if you still get high CO readings, you have to clean the heat exchanger and that's a big, dirty job if you do it properly.

EBEBRATT-Ed

Something is wrong with only a 183 stack temp. Sounds like way to much air or not enough fuel

icy78

12.8% 02 is way underfired. Should be seeing 6-9% and below 100ppm on the CO.
Please post some pics. 

Sweet_Lew

Sorry, been a crazy night. Will get pics tomorrow. Can someone help me understand what underfired means? Can that possibly be fixed by adjusting or replacing the gas valve? I just checked and the valve was manufactured in 2001 which makes me think it is the original. It's a Honeywell VR8204A 2175 which was discontinued in 2018.

STEVEusaPA

Proper gas pressure and maybe an orifice change may be in order. But you can only do it with a manometer and a combustion analyzer...and you actually have to know what you are doing.

icy78

If the technician took his readings above the draft Hood..... Then I could see really wacky numbers like he posted. It would mean that the CO was even worse than what the analyzer shows. But it may explain the 12.8% O2 and the low stack temp.

 let's say that he did in fact take the readings in the wrong place, then it's possible that the appliance is actually way over fired and that will give you that crazy C0 number.

Sweet_Lew

First tech probed past the draft hood about 2 feet. Just had a second tech show. He also ran a CA and got similar numbers (he probed the flue entry). His theory is due to a clogged\sooted heat exchanger. He also made a good point that he could clean the HX for quite a bit of money. Then, who knows if the 18 year old aquastat fails next year and that's even more money. I'm leaning towards a new boiler at this point.

STEVEusaPA

Don't use the same techs/company

Sweet_Lew

Pics attached...You can see where he covered the hole with the tape.

mattmia2

Since that is a converted gravity system and has a lot of mass it is probably running lower water temps a lot of the time and that caused it to soot up.

As far as spending the money to clean it, it could fail tomorrow, it could last another 30 years. If the system doesn't leak so it doesn't see fresh water it is likely to last on the longer end of the spectrum, although the condensation from the lower temps do shorten its life. After it is cleaned, setting the thermostat to run longer cycles could help it stay clean longer.(also cleaning it more often before it gets as bad as it currently is.)

Zman

I agree with @mattmia2 that the boiler is likely condensing. This could be causing buildup on the top of the heat exchanger. The boiler should really be piped with an anti condensing bypass loop.

Try turning off the boiler and letting it cool and then take a picture of the top of the heat exchanger. You can usually stick your phone into the draft hood on the front and take a picture straight down. It will take a few attempts but stay with it. My guess is that the top of the exchanger was not cleaned and is covered with "dandruff".

Where does the vent go after the pictures? What is the condition? I would suggest inspecting it as well, with condensing going on in the boiler it may be damaged. Look for rust or evidence on a water drip on the pipe and cap.

icy78

    Those CA readings were taken AFTER the draft hood. WRONG LOCATION.! So the reading is from diluted flue products and is basically useless.
       If, the draft hood is working at it's designed 40-50% dilution air, say at 70 degrees, then if  50% of the flue gas is at 70f, (thru the drafthood) then in order to see 184 in the flue pipe , that says that the other 50%, which is ENTERING the drafthood is 300 degrees.  
Good chance it's not condensing, altho it's close, depending on outlet water temp at the time.
You need someone on site to fix the Combustion/dirt problem/ or issue caused by the draft hood itself. That issue would be it allowing TOO MUCH dilution air.
Fixable via barometric damper and drafthood blockoff.   Set up with combustion analyser.
Seen many high draft situations cause this problem so it could be that too.
Could be a few things.
I converting 4) 1.5mbtu boilers soon that all run 200-3700 ppm C0.
All proved thru drafthood blockoff with cardboard, that air up the hood, instead of thru the boiler, caused the combustion problems.
 Can you post a flue draft reading?

icy78

I forgot to mention that too much dilution air causes the boiler to not vent properly into the draft hood, resulting in low 02 , high C02. the C02 cant vent properly and mixes with the primary and secondary air resulting in more C02, less 02 now. This results in more C0 (carbon monoxide).

Deadly cycle.
I'll say it again.
Dont run that boiler until someone competent has serviced it.
Life and death issue.

icy78

The readings should be taken in/at the breaching. It may take 3 or 4 readings dependent on cells. These readings will give a profile of the boiler across the burners. 
 Must be done in conjunction with flue draft reading,  best done with a seperate draft gauge.

Sweet_Lew

Zman said:

Try turning off the boiler and letting it cool and then take a picture of the top of the heat exchanger. You can usually stick your phone into the draft hood on the front and take a picture straight down. It will take a few attempts but stay with it. My guess is that the top of the exchanger was not cleaned and is covered with "dandruff".

Here are a few pics of the HX. Thoughts?

icy78

Lew, look up NCI (national comfort institute) Contractor locator. Combustion certification.
One of those guys will get you fixed up. 👍

Zman

I have to agree with @icy78, the combustion measured at that point is not accurate.

Your heat exchanger looks good, I am not sure I see any point in hauling that one out, only to haul another in. I think it is time to hire someone competent to inspect the vent and figure out what is going on with the gas train.

Sweet_Lew

Thank you all for the help! I located a contractor on NCI's consumer site who is certified in Carbon Monoxide Safety & Combustion Analysis. They will be coming out today.

Sweet_Lew

Technician came out from the company on the NCI site. He probed up the flue entry up by the damper. His readings were WAAAAAY different. 1.9 O2 and 50 CO! He adjusted the gas valve and got the readings to 5 O2 and 1 CO. Stack temp was also over 300 degrees vs 183. We let the boiler run for a while and he re-tested to make sure the readings were the same and they were. However, he measured draft and it was OK, but low. Since their readings were OK\safe, their recommendation was to install barometric dampers for the boiler and hot water heater and block off the draft hood entry. I think Icy nailed it in a previous post.

STEVEusaPA

The NCI tech was the only professional in your home.
Thanks for reporting back. Seems like you uncovered some very inexperienced techs (actually the type who want to condemn your equipment and sell you new stuff).
An uninformed and/or trusting person would've been duped into dropping some serious money on an unneeded new boiler.
There's a very large hvac company in my area that ALWAYS finds a cracked heat exchanger on any unit they didn't install over 10 years old, and scares the h/o with the 'deadly carbon monoxide could leak into your home' tactic.

Sweet_Lew

I know enough about my system and to tell me I have a cracked heat exchanger, I'll call BS. Unfortunately, it took 3 companies and hundreds of dollars later to get a skilled tech that didn't want to throw a boiler at me and actually troubleshoot. If I could buy you all a beer, I would. I truly appreciate all the help.

Zman

The logistics would be tough but I think a "Buy-a-Beer" tab would be awesome. Maybe after you get 12 points, they send a 12 pack. I am sure @Erin Holohan Haskell can work that out

The vague "Cracked Heat Exchanger" diagnoses flies better on forced air furnaces. With hot water boilers, the whole "high pressure goes to low pressure" and "water ends up in a puddle on the floor" highly scientific concepts sort of make it a hard sell.

I am glad it all worked out.

icy78

I'm sure he'll do it, but make sure spill switches are installed on those barometrics.
      Also did he do a combustion air/venting test. Meaning running all home exhaust fans, while checking draft.  Also draft check with the water heater also firing.
     Low draft MAY mean not enough combustion air or a venting problem. Make sure he covers it all.
I'm really glad  you found  someone to fix the issues.!👍

unclejohn

My brain is not as big as most of the people on here but I would not do a thing to that boiler other then run it.

Erin Holohan Haskell

Zman said:

The logistics would be tough but I think a "Buy-a-Beer" tab would be awesome. Maybe after you get 12 points, they send a 12 pack. I am sure @Erin Holohan Haskell can work that out

We'll get started on that right away.

unclejohn

Speaking off beer...
https://www.youtube.com/watch?v=L8mcy5MhBgc

icy78

Erin Holohan Haskell said:

The logistics would be tough but I think a "Buy-a-Beer" tab would be awesome. Maybe after you get 12 points, they send a 12 pack. I am sure @Erin Holohan Haskell can work that out

We'll get started on that right away.

YES!

icy78

@Sweet_Lew .
I think, that on that boiler, he shouldve taken about 5 readings, same area where he took the one reading but giving a cross section sampling.
I've seen 0 CO at one end and 3500 at the other on some installs. Or a bad one in the middle. This is important, because it can/will lead to a source of High C0.
5% 02 is on the really low end , altho it may work for that particular boiler in that particular install. Looking for....
6-9% 02. Less than 100 as-measured C0 ppm. Shooting for <30ppm C0.

Sweet_Lew

@icy78 , he took multiple readings. They are here now installing the dampers AND spill switches. Will post a pic once they are done.

captainco

Usually if someone touches your equipment and then tests it and find it unsafe, they broke it and owe you all your money back!! Glad you were able to find a qualified contractor. Thanks to all of you who helped!!

Sweet_Lew

Done!

STEVEusaPA

@captainco, is that tee for the baro correct? Just wondering.