Puff of fuel smell from barometric damper on startup
The saga continues with my annoying AFG issues. (History here https://forum.heatinghelp.com/discussion/194271/beckett-afg-efficiency-testing-boiler-sooting-issue)
About a month ago I opened up the firebox and did my usual cleaning, paying particular attention to the heat exchanger fins. Overall, there was very little sooting. Fired up the boiler, did multiple smoke tests which all showed 0 smoke. Not ideal, but given the history here I'll take the efficiency hit to avoid sooting.
Each morning when I come downstairs to the basement, there is a smell of fuel oil. I have phantosmia, which is just great for problems like this, because I can never be sure whether I'm smelling what's actually there or not. I've had my FIL walk through the basement and he claims it smells "normal" to him for a home with oil heat, but it just seems wrong to me. I have ruled out oil leaks in the system. All possible leak points are dry, oil pipe from tank is new, there is no trace of leakage anywhere.
This morning I happened to be down in the basement, went into the boiler room to see whether I could figure out exactly where the smell was coming from. Sniffing all the joints / gaskets / etc. Sniffed around the barometric damper, nothing. Suddenly, call for heat. The AFG turns on, goes through it's 15 second pre-ignition routine, fires. Big puff of exhaust hits the barometric, right into my face - bingo. Strong fuel smell. Barometric then opens as expected to maintain draft.
What would be the most likely root cause here? Filters are all good, running a 10 micron and a Tigerloop. The AFG has a CleanCut pump. Brand new nozzle, precisely aligned electrodes. . I've eyeballed the firebox through the port at shutdown, see no evidence of any kind of lingering burn / drip. No oil in the air tube. No sooting around the barometric.
Comments
-
How's the flue? When the boiler is off and cold, how open is the damper? Can you feel any downdraught through the damper (unlikely, but worth asking) when the boiler is off?
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
a slightly delayed ignition can be the cause. Are the electrodes properly adjusted? Is the nozzle partially plugged? Do you have too much excess air? (that can blow the spark cooler or the oil away from the spark) It could also be a combination to things. What are your combustion test numbers (I know you have a zero smoke) What is the over fire draft, stack temperature, and CO2.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
0 -
I skimmed through the other thread and my first question is the same as Jaime- describe the chimney, flue, height, diameter, liner, and chimney connector pipe.
If you have a tall oversized, cold, or restricted flue, you can get a lot of back pressure. 15 seconds may not be enough pre-purge. Go for 45 seconds. You may need to change the primary control.
Chimney draft readings should be taken btw the baro damper and the chimney- not just outside the boiler. That's where you take combustion analysis readings- about 1.5-2 duct diameters downstream of the appliance collar or any turns, dampers or draft controls. You should only need about -0.02 to -0.03 wci in the stack.
Once you've gotten your chimney in order, THEN tinker with the equipment.
0 -
I also skimmed the other thread and saw a spot where you said "I don't have an analyzer at this time." (Paraphrasing), so wondering if there are any combustion numbers. Because too much excess air will cause a delayed ignition. A cold boiler and chimney will compound that.
Keep in mind, a properly tuned burner, with zero smoke will always have a split second of positive pressure in the breach before it goes negative. The regulator should have a stop to prevent the damper from swinging out. Ignition should be smooth.
0 -
Damper is fully closed in this state. I have not felt any downdraught but haven't been looking for it specifically.
Electrodes are adjusted to 1/4” above center of nozzle, 1/8” in front of nozzle and gap 5/32” (per AFG manual). Nozzle is brand new. I don't have a combustion checker of my own and would need to rent one or get a tech in here to get those, unfortunately. The last check that was run on this unit was on 1/10/24 and was:
379.5 F = Temp Stack
4.3% = Oxygen
7 ppm = CO
12.47% = CO2
84.7% = Efficiency gross
25.9% = Excess Air
-0.029 in-H20 DraftHowever, this was before I pulled out the AFG's low firing rate baffle, so these numbers have changed I'm sure.
Flue is 32' vertical feet of 6" stainless liner in a masonry chimney, from top to the back of the unit, with two 90° stainless elbows. Had it swept last fall. I can tell you that all the draft numbers I've ever pulled, or seen third-party techs pull, have all been between the unit and the baro, not between the baro and the chimney… I will keep this in mind for the next time I perform a combustion test.
Yeah, no combustion numbers right now. The stop on the damper does prevent it from swinging outward, the smell and exhaust puff I felt came around the edges of the damper.
Sounds like I need to do another combustion test… will see about renting the unit again.
0 -
If the damper is just hanging fully closed when things are cold, there is little or no initial draught. Lots of possible reasons for that — but it will tend to produce a puff when the boiler lights off.
I know this sounds off topic, but has any work been done in the building recently to reduce air infiltation? Or installation of an exhaust fan?
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
OK, this is good to know. I will say that in cases where it is very windy outside I will hear the damper flutter open and close as gusts blow across the roof.
No work has been done to reduce air infiltration or increase ventilation, although the house is pretty "tight" with modern windows, etc. I have cracked a window in the boiler room for additional ventilation and to try and reduce a bit of the fuel smell, so there is some directly adjacent ventilation (8 feet or less) to the damper. The burner also has a fresh air intake (I've verified it is clear and not blocked).
A bit of additional information; I was down in the boiler room (workshop) this evening, which means that the system was working quite a bit due to the outside temp dropping. I noticed that the "puffs" from the damper smelled much less of fuel and more like combustion / exhaust, probably because it's running more frequently and there is more latent heat headed up the flue, improving draft.
Another thing that occurs to me, and I feel like a dummy for not realizing it… this issue really became noticeable after I deleted the Field Controls OVD that I had installed initially, primarily because it died twice in 4 years and left me in a no-heat situation both times. My guess is that holding that heat in the boiler meant that the 15 second pre-purge has to work harder because the boiler is cooler.
I may be picking up the controller that will allow me to change the pre-purge duration.
0 -
Put back in the low firing rate baffle. Removing that drastically affects combustion. You shouldn't have done that without combustion testing equipment. As said earlier in the thread, high excess air affects ignition. The low firing rate baffle decreases air to the burner.
0 -
Noted. I have a combustion tester on order now, will update the thread once I've gotten some new numbers and replaced the baffle
0 -
@skybolt_1, as a rule, any change in the air or oil that goes into the combustion process requires a combustion analysis. Removing the low air baffle would qualify as a change in the air. removing that baffle means that you have more air. More air can blow the oil away from the spark, if the oil blows way from the spark it will take a short second for the retention head to cause a venturi effect to bring the oil back to a place where it may ignite. That extra second of extra oil will cause a significant puff.
I think you need need an adjustment that will bring the air oil mixture in line with each other.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
1
Categories
- All Categories
- 86.4K THE MAIN WALL
- 3.1K A-C, Heat Pumps & Refrigeration
- 53 Biomass
- 423 Carbon Monoxide Awareness
- 94 Chimneys & Flues
- 2K Domestic Hot Water
- 5.5K Gas Heating
- 101 Geothermal
- 156 Indoor-Air Quality
- 3.5K Oil Heating
- 64 Pipe Deterioration
- 926 Plumbing
- 6.1K Radiant Heating
- 383 Solar
- 15.1K Strictly Steam
- 3.3K Thermostats and Controls
- 54 Water Quality
- 41 Industry Classes
- 48 Job Opportunities
- 17 Recall Announcements