How close to get Combustion Analysis to Specification for a Modulating Condensing (Mod-Con) Boiler?

Users who are viewing this thread

amodedude1

New Member
Messages
3
Reaction score
0
Points
1
Location
Philadelphia
I have a recently installed Noritz CB-199-DV-NG Combination Boiler in my home. Since the installer did not perform a combustion analysis upon commissioning I decided do buy a Testo 510 Digital Manometer and a Bacharach Fyrite Intech combustion analyzer to do the analysis myself. I have learned a lot about the process and am still learning (you can read though my saga here ).

My question is, how close to the service manual specifications does one need to get when performing a combustion analysis?
Have you ever had a situation where you couldn't get it 110% within spec of the service manual and is that OK?

For example, the Noritz CB-199/CB-180 Service Manual is very specific in saying that for CO2 on a 3" Vent and NG, I should be seeing a CO2 of 7.1% CO2 (+-0.1%) @ -0.10" W.C. on LOW FIRE. Then on HIGH FIRE, the specs say that I should have a CO2 of 9.1% @ -0.36" W.C.

Noritz CB CO2 Values.PNG


I initially made a few mistakes with my testing such as not turning on enough faucets to dump enough heat to allow the boiler fan to actually ramp up into high fire mode, but that's besides the point. Also my AGM ended up failing which I had to replace and was throwing Error Code 67 randomly but that has been fixed now.

Long story short, I was able to get the boiler very close to the service manual specifications with some minor adjustments to the offset screw. My most recent test results results are:

LOW FIRE (@ adjusted to exactly -0.10"W.C.)
---------------
O2 6.8%
CO 11ppm
Eff 99.5%
CO2 8.0%
T-Stk 69F
T-Air 47.7F
EA 42.8%
CO(0) 16ppm


Normal FIRE
---------------
O2 5.9%
CO 24ppm
Eff 95.2%
CO2 8.5%
T-Stk 106F
T-Air 48.5F
EA 35.0%
CO(0) 33ppm


HIGH FIRE
---------------
O2 5.0%
CO 62ppm
Eff 88.5%
CO2 9.0%
T-Stk 133F
T-Air 48.2F
EA 27.8%
CO(0) 81ppm

So my question again is, if you look at my low fire, I have the offset screw adjust to where my manometer was reading exactly the specified gas pressure BUT my CO2 is off by 0.9% while the manual says it should be +/- 0.1%. How accurately do you folks adjust your boilers upon commissioning? If the boiler is running great, should I worry myself over the low-fire readings being off a bit? Knowing that things like air temperature and variations of incoming gas pressure can effect the combustion due to changes in air density ext, and the fact that my boiler is installed in the real world (not some lab with perfect conditions), how arcuate is the stipulation of +/-0.1% imposed by the manual?

When you folks install how close is good enough? How close do you normally get it? Curious what your experiences have been. Thanks!
 
Last edited:

Fitter30

Well-Known Member
Messages
2,610
Reaction score
404
Points
83
Location
Peace valley missouri
Since there not giving a spec on normal fire setting low and high should get heater close enough. Co try to get it below 50 ppm hi fire o2 at 5% looks a little lean. Sure u noticed that even a small adjustment changes readings. Flue length will change the reading.
 
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks