Combustion analysis/burner setup question for Buderus/AFG

jkfoote

Sent this to Beckett Tech Support last week, but no response yet; wondering if I'm on the right track:

On an AFG burner with band and shutter at the full open positions (B-10, S-10) I’m only able to bring excess air up to 14%, with a smoke test at number 1. Figure 61 in the Professional Guide to Oil Heat document (pg 45) says I should try to get to excess air of at least 20 percent.

The implication is that I’m getting too much fuel oil into the boiler for the air handling system to supply(?). The boiler is located in a garage, so I opened the garage door and reran the analysis - there was a slight increase in O2 levels, but not enough to get EA above the 14% I saw with the door closed.

Should I shift down to a nozzle with lower firing rate to try to get to 20 percent EA? And if so, any recommendations on the next sizes to try?

- Jim

Details:
New Buderus G-115-5 boiler
Setup matches the ‘G115-5 AFG’ line from the Beckett OEM Specification Guide (pg 20):
AFG burner with L2 combustion head, AFG90MPASN air tube
0.85 x 60 degree type B nozzle
Oil pressure 140 psi
Flue gas back pressure 0.06 inches of water column draft, in accordance with Buderus spec
Overfire pressure slightly positive
Net stack temp at steady state is 350 degrees (4 of 6 boiler baffles removed)
Chimney vent system, total length 30 ft with three 90 degree bends (7’ of 5” dia, 23’ of 6” dia), just cleaned out

Combustion Analyzer: Forensics Detectors Model FD-4A, last calibrated Aug ’22.

I can also post plots of O2 and CO against band and shutter position, but don't want to flood with too much data in one post!

Steamhead

Check the head adjustment, bring it into spec if it's not. This does affect the air flow thru the burner.

captainco

Is this a new boiler or old? Positive overfire sounds like possible restriction in the boiler. Flue temperature is also low for oil which also indicates possible restriction. O2 and excess air are the same thing. Excess air is calculated from the O2. Why they call the air that is needed for clean combustion excess? I don't know?

R Mannino

Is it possible there is a low firing rate baffle installed in the burner?

Kickstand55

Be sure to check breech draft even though the chimney seems ok. Is it a cold chimney on an outside wall?
Check the nozzle data to be sure it's the right nozzle. Sometimes the wrong nozzle is installed new, not often though.
Then check the "Z" dimensions with the gauge. Be sure you're setting it for an "L" head not a "V" head.
Check the fan housing for debris in the fan or cone.
If this doesn't work, try another nozzle of the same type.
If that hasn't changed anything, try going to a .75 nozzle.
Let us know if anything mentioned here worked. It helps us too.

HVACNUT

Is that 30 ft. flue run before it get to the chimney, or does that include the chimney?

The over fire draft is positive 0.06? I believe Buderus specs 0 to slightly positive. 

If there's 30 ft. of horizontal flue, I know from past experience that the 115 does not like that very much. 

BDR529

Install proper Riello burner, amount Bio in tank.

jkfoote

Sorry for the slow response - lots of power outages keeping me busy.

@Steamhead - Thanks, that was a good suggestion.

The OEM guide specified the L2 head unit with AFG90MPASN air tube. The L2 head isn’t shown in the T501-GAUGE.pdf tutorial from the Beckett web site, but my understanding is that the setup is the same as for the L1 head - using the T501 gauge I’ve double checked the depth to be at the ’C’ mark for a conical tube, or a Z dimension of 1-3/4”. That matches the line in the Beckett Residential Oil Specification Guide for a Buderus G115-5 with AFG burner, .85x60B nozzle and 140psi oil supply. Photo attached - it’s a conical shroud right - not straight?

But the thought is a good one - maybe something keeping all the air that supposed to be delivered from getting though the air tube? The blower fan looks good and the coupler to the motor looks good. The fan is definitely turning when the burner is running. I pulled out the nozzle assembly and looked for any obstructions in the air tube - everything looks clean enough. I suppose the motor could be turning at an RPM that’s below spec? Maybe I can dig up an old fashioned strobe tach and check that. I think it has to be turning in the right direction, otherwise the oil wouldn’t flow. Anything else I should check?

I guess the other possibility could be too much fuel oil going in. I tried changing nozzles and got the same results. I’d already adjusted oil pressure to 140psi, but maybe my oil gauge is off? I can try another.

(I'll get answers to the other responses ourt shortly - thanks for the help!)

jkfoote

@everybody - Thanks for the help!

@captainco
New boiler.

> Flue temperature is also low for oil which also indicates possible restriction.

Yes. I was surprised to have to remove 4 of 6 baffles in the boiler to get the flue temp up to 350 degrees net. At the original air settings (B-3, S-10) the combustion was very poor with all baffles in place, with high CO and lots of soot generated. Cleaned out the boiler and flue thoroughly, fiddled with baffles, then gathered the analysis data attached. But certainly possible I missed something. Anything specific I should doublecheck?

Yes, understand EA is calculated from O2. Plots show O2 and CO measurements, EA is from the meter’s calculations which look reasonable for these O2 levels.



@R Mannino
>low firing rate baffle installed?
Yes, a low firing rate baffle is installed. But I think it’s supposed to be there, right? The AFG manual says:

The LFRB is sometimes used for firing rates under 1.00 gph as listed in Table 4. Refer to the appliance manufacturer’s instructions. Do not omit the LFRB when specified. Omitting the baffle when specified or installing the baffle when not specified could result in impaired burner performance.

Table 4 doesn’t show a spec for L2 heads, but for L1 it says that it should be installed for flow rates up to .85 gph. ‘Up to .85 gph’. Hmm. So baffle or no for .85? If I switch to .75 then for sure baffle.


@Kickstand55
Yes, I’ve checked breech draft. My manometer reads -0.06 in wc after adjusting the barometric draft regulator and before taking the measurements shown. But I guess my manometer could be lying. I guess I can set up a tubing loop and do a check.

Yes, cold chimney on an outside wall. What’s the implication? It’s all single wall galvanized flue pipe - 90 degree out of the boiler, then 18” vertical to sample hole, 10” vertical to draft regulator, 10” vertical to 90 degree, 18” horizontal to thimble, 24” horizontal to outside wall, 90 degree, then 25+ feet vertical to about 6’ above the 2nd story roofline capped with spark arrestor. All of the flue outside the wall is framed in and I assume insulated (?). Certainly cold when it first starts up, but probably not cold after 10 minutes of operation before measurements start?

Yes, double checked the nozzle. The very first nozzle was the wrong pattern (hollow vs solid), but the next two matched the spec: .85x60B and this is what was used to measure the data shown.

Yes, double checked Z dimension - see note to Steamhead above.

Yes, checked for debris in fan and cone - certainly not pristine, but pretty darn clean.

Yes, tried another nozzle of the same type with the same results.

Yes, I like the idea of trying the .75 nozzle - just wanted to get some second thoughts on it first.

@HVACNUT
Flue is mostly vertical - see description above.

I’ve cleaned it out twice from the thimble using a flexible brush with bendable rod segments. Saw the expected amount of junk out on the first clean, little out of the second.

I haven’t been to the roof to inspect the spark arrestor, but visually from the ground it looks clear and at the original band and shutter settings was passing plenty of smoke!

No, draft at the sample hole is -0.06” wc. Draft over fire is slightly positive.

@BDR529
Yes, if all else fails moving to the Riello burner is an option. But Beckett’s specs say this setup is supposed to work, and before replacing the burner it’d be good to know if there was a boiler or flue restriction problem etc. that a new burner wouldn’t fix.

Your note about Bio in the tank is interesting. The fuel oil delivery company is billing for the additive, but who knows if it’s actually going in. No sign of crud in the filter, and getting good fuel oil pressure at the burner. Any way I can check for bio myself?

But what if the wrong fuel was delivered - could that account for these combustion numbers?

MikeAmann

jkfoote said:

> AFG burner with band and shutter at the full open positions (B-10, S-10) I’m only able to bring excess air up to 14%, with a smoke test at number 1.
> Flue temperature is also low for oil which also indicates possible restriction.
> I was surprised to have to remove 4 of 6 baffles in the boiler to get the flue temp up to 350 degrees net.
> draft at the sample hole is -0.06” wc. Draft over fire is slightly positive.
> I haven’t been to the roof to inspect the spark arrestor, but visually from the ground it looks clear and at the original band and shutter settings was passing plenty of smoke!

Even I know that this means that there is a restriction. You just haven't found it yet.
Bird, squirrel, something is blocking the flue gas from exiting the chimney.
Or is your boiler room so airtight that there is not enough air to support proper combustion?

MikeAmann

Just to be clear, this is your combination, correct?
https://www.ecomfort.com/Buderus-G115WS-5-AFG/p72593.html?gclid=EAIaIQobChMI5JqV66eT_AIVagGtBh3iXgBPEAQYAiABEgIUAPD_BwE

With these settings:
Buderus G115-5 AFG B2007 L2 2¾" 0.85 X 60°B 0.85 X 60°B (B) AFG90MPASN 58020080 140 S-10 / B-3 * Electrode settings of ¼" above center of nozzle, ⅛" in front of nozzle and gap 5/32". With conic shroud "Z" dimension is 1¾".
https://www.beckettcorp.com/support/burner-settings/

DJD775

jkfoote said:

@R Mannino
>low firing rate baffle installed?
Yes, a low firing rate baffle is installed. But I think it’s supposed to be there, right? The AFG manual says:

The LFRB is sometimes used for firing rates under 1.00 gph as listed in Table 4. Refer to the appliance manufacturer’s instructions. Do not omit the LFRB when specified. Omitting the baffle when specified or installing the baffle when not specified could result in impaired burner performance.

Table 4 doesn’t show a spec for L2 heads, but for L1 it says that it should be installed for flow rates up to .85 gph. ‘Up to .85 gph’. Hmm. So baffle or no for .85? If I switch to .75 then for sure baffle.

The Beckett OEM spec guide does not call for the use of a low firing rate baffle with the G115-5. The dash after the nozzle is where the baffle part number would be specified.

jkfoote

@MikeAmann

Thanks for the help!

> Or is your boiler room so airtight that there is not enough air to support proper combustion?

I wondered the same. The ‘boiler room’ is actually a garage, so I re-ran the combustion test with the garage door open. I did see a slight improvement in O2 levels vs. band/shutter position, but not enough to bring EA any higher (still tops out at 14% EA with band and shutter at full open).

I’m with you, this is too dramatic a delta from the Beckett/Buderus spec setup; it really has to be something dramatic.

> Just to be clear, this is your combination, correct?

Very close:
Boiler is as shown in your link.
Burner is AFG, but not a new unit. It’s the old burner from the boiler this replaced. The burner nameplate reads:

Model ‘AFG’ Series Burner
MP1192
Made in the USA
0.5-3.0 GPH, 120V, 60 Hz, 5.8 AMPS
Comm. of Mass - State Fire Marshal Approval #BEC-88-01, Approved July 1, 1998
Accepted N.Y.C. MEA. 212-83-E
Mfg. by R.W. BECKETT CORP Elyria, Ohio, USA
6519 REV 3

I believe it was manufactured in 1992, but hardly any of it is original:
The motor is a new Beckett 21805, Model Y5L271C81
The oil pump is a Suntan B2VA-8216
The primary is a Honeywell R8184G 4009
The ignition transformer is Allanson 2275-628G
The air tube is a Beckett AFG90MPASN

> With these settings:
Yes, with all those settings except band and shutter - if I run at S-10, B-3 the CO levels are way too high. And except for...

@R Mannino
DING DING DING - now we’re getting somewhere! My bad, sorry for the churn.

This is very likely the root cause, or at the least a substantial contributor. Power is out right now so I can’t check it, but I’ve removed the LFRB and will rerun the combustion analysis once we get power restored, and I’ll report back.

Thanks!

MikeAmann

Your .85 gph nozzle at 140 psi gives a firing rate of 1.01 gph.

If you want to keep the .85 gph firing rate, then choose a .70 nozzle (if that size exists).
This firing rate puts you right at the break point as to whether to use the LFRB or not.
The combustion analysis will have to determine which way you go.
Remember, it's firing rate that determines this, not nozzle size.
https://www.beckettcorp.com/bulletins/understanding-the-low-firing-rate-baffle/

HVACNUT

Agree with @DJD775, that the LFB is not spec'd for your setup.

It looks like the proper insertion depth from seeing Z dimension pic. Is it at 6- 1/4"?

-0.06 at the breach is waaaaay too much draft. Buderus wants -0.02.

jkfoote

@MikeAmann - Thanks for the notes and reminder on firing rate.

@HVACNut - Thanks for the note.

> It looks like the proper insertion depth from seeing Z dimension pic. Is it at 6- 1/4"?

Yeah not my best photo - sorry! It’s off angle so it looks like the shroud is protruding past the ‘C’ mark on the T501 gauge, but if you look straight down from the top it’s aligned. No, not 6-1/4”; the spec (see the far right note for conical shroud) and the ‘C’ mark on the T501 are both 1-3/4”.

> -0.06 at the breach is waaaaay too much draft. Buderus wants -0.02.

Hmm - this table is from the Buderus installation documentation:


It says ‘Flue gas back-pressure’ should be 0.04-0.06” w.c. - am I reading this spec wrong also?

But that said, with the LFRB removed I’m getting unstable flame at startup which could indicate too much draft (?). I shutdown, replaced nozzle, double checked electrode positions and verified that the AFG Air Guide was installed. Now waiting for the system to cool down so I can get a longer startup run time to fiddle with band and shutter settings. I’ll see if lowering the flue back pressure helps and report back.

DJD775

@jkfoote
There is conflicting information in the manual on pg. 18:

BDR529

After reading again your trying to set to #2 fuel oil lab specs. Real world blended fuels that is where the deviations come in.

Get a good light with a clean fire and go fron there. You will never get lab numbers without their fuel.

WMno57

jkfoote said:

The motor is a new Beckett 21805, Model Y5L271C81

Is the new motor moving the correct volume of combustion air? Correct speed? Correct rotation? Missing fan blades? Fan on backwards?

MikeAmann

You should be using the 2-3/4" static disk. I don't know if you verified that yet.

jkfoote

@ Everybody - Thanks again for all the help. I think it’s all working correctly now - summary below.

@BDR529 - Thanks for the note. Yes, understand that field and lab setups will never exactly match. But in this case there were serious problems (mostly RTFM, sigh) that were highlighted by how far the combustion analysis results were from the lab setup.

@WMno57 - Thanks for the note and good thought. I definitely haven’t yet proven that the new motor is moving the correct volume. I’m now pretty sure it’s moving the correct direction and fan blades, mounting gap, orientation look good and also matches the pump expectation. But won’t know about speed until the strobe tach I’ve ordered arrives.

@MikeAmann - Thanks again for the notes - though this one made my heart sink. Three RTFM errors would have been too much! But double checked it and yes, correct part 3383, 2-3/4” static plate installed.

But thanks to everyone’s help (and especially to comments from @R Mannino, @MikeAmann, @DJD775, @HVACNUT) I think I now have a correct setup. The combination of removing the LFRB, adjusting draft, and returning to the recommended B-3, S-10 position resulted in stable fire. Quick combustion analysis results: O2 4.2%, CO 25ppm, COAF (computed) 32ppm, EA (computed) 24%. I’ll probably fiddle with a lower firing rate setup once nozzles arrive - if so I’ll report back.


Summary:
Two operator errors in reading/interpreting the specs/documentation:

1. Missed the note from the Beckett OEM Specifications Guide for Residential Oil Burners for this Buderus G115-5 boiler: Low Firing Rate Baffle should not be used.

2. Missed the note from the Buderus installation documentation that directed setting breeching draft to -0.01 to -0.02 inches WC after initial startup.

The moral is the usual: study the documentation carefully.


Again, thanks to everyone for the comments and advice, I owe you all a beer at the very least! My impression is that y’all are mostly in the North East? If so, I’m happy to deliver on my debts when I make my road trip east next fall!